Gas/Fuel vapors/fumes visible from gas door

[bloc]

I can definitely fit the reservoir, pump, and fuel cooler here in the engine bay, and it's conveniently right next to the battery and the last section of return fuel hose that wraps around back of the engine before it connects to the hard line, which is a good tie-in point. Then I would then route coolant lines up front to a small radiator that I already confirmed will fit behind the grill, giving it the coolest air possible.

Unfortunately, it means if I want onboard air at some point, then it can't go here. But that's okay.

View attachment 3676934
View attachment 3676937

So is the plan to tie in to fuel return after the rail? Meaning heat soak under the vehicle could still be a concern?

 

[FerrisBueller]

So is the plan to tie in to fuel return after the rail? Meaning heat soak under the vehicle could still be a concern?

Correct, but that hose runs so close against the back of the engine, I suspect it's picking up the most heat at that point before it gets under the vehicle. Plus the close proximity to nice cool air for the radiator behind the grille means a very large temperature differential between the hot fuel and cold coolant, removing potentially the most heat.

 

[FerrisBueller]

By the way, this also means that even if a lot of heat gets added under the vehicle, a large portion of that heat will still get removed once the hot fuel from the tank comes back around to the engine and hits this cooler again. Having a cooler anywhere in the line will help remove accumulated heat.

 

[TheGrrrrr]

This may be an absurd thought, but I was just looking at those frog togs cooling towels? I had one in my golf bag for years and loved it playing in the arizona summers. What if I were to take like 3 of 33x13 inch ones and coat the inside of the factory fuel tank skid with them, to the point where they were sort of sandwiched between the skid and the tank itself. When conditions warrant, some water could be sprayed up under the truck soaking the the material and providing evaporative cooling for much longer than a simple quick spray of water to the surface of the tank would.

My thinking isn't for normal everyday use, but instead for the Moab or Colorado trip in the summer months, where you could plan ahead with some water on hand for the purpose. Not a great solution, but maybe effective in the right situation?

Spoiler Alert: Its a dumb idea.

 

[TheGrrrrr]

Okay decided to log some data and then asked Gemini what it means and I think I found part of the problem:

I tracked the following during a 5pm drive in 113f heat alternating between surface streets and freeways:

1. Command evaporative purge: Bounced between 0% and 100%
2. Evap (Purge) VSV: Almost always matched "Command evaporative purge"
3. EVAP Purge Flow: never saw it higher than 6.5%

According to Gemini, in a system working correctly the three metrics should have tracked relatively close to each other:

Absolutely! Let's break down the relationship between these EVAP (Evaporative Emission Control) system metrics:

Commanded Evaporative Purge (%)

• What it is: This is the target or desired amount of fuel vapor purging that the engine control module (ECM) wants to achieve. The ECM calculates this based on factors like engine load, temperature, and driving conditions.
• Why it matters: It sets the goal for how much fuel vapor should be pulled from the charcoal canister and into the engine for combustion. This helps reduce emissions and improve fuel efficiency.

Evap (Purge) VSV (%)

• What it is: This is the duty cycle (the percentage of time it's open) of the purge control solenoid valve. This valve is the gatekeeper that regulates the flow of fuel vapor from the charcoal canister to the intake manifold.
• Why it matters: The ECM controls the Evap (Purge) VSV to match the Commanded Evaporative Purge as closely as possible. A higher duty cycle means more vapor is being purged.

EVAP Purge Flow (%)

• What it is: This is the actual amount of fuel vapor being purged, often expressed as a percentage of the maximum flow rate the system is designed for.
• Why it matters: It shows how effectively the system is removing fuel vapor from the charcoal canister. Ideally, this should closely match the Commanded Evaporative Purge. If it doesn't, there might be a problem with the purge valve, the charcoal canister, or other components.

The Relationship

1. ECM Commands: The ECM determines the Commanded Evaporative Purge based on driving conditions.
2. VSV Opens/Closes: The ECM adjusts the duty cycle of the Evap (Purge) VSV to control the flow of vapor.
3. Vapor Flows: The EVAP Purge Flow reflects how much vapor is actually being pulled into the engine.
4. Monitoring and Adjustment: The ECM continuously monitors the EVAP Purge Flow and compares it to the Commanded Evaporative Purge. If there's a discrepancy, it adjusts the Evap (Purge) VSV to try and correct it.

Example:

• Commanded Evaporative Purge: 50%
• Evap (Purge) VSV: 48% (The valve is open 48% of the time)
• EVAP Purge Flow: 45%

In this example, the system is working fairly well, but the ECM might slightly increase the VSV duty cycle to try and get the actual purge flow closer to the commanded value.
So why would the actual be greatly lower than the 100% being asked for?
Gemini says:
If the EVAP Purge Flow is significantly lower than the commanded purge and VSV duty cycle, it indicates a restriction or blockage in the EVAP system, preventing the fuel vapor from flowing freely. Here are some common causes to investigate:

1. Clogged EVAP Canister: The charcoal canister is responsible for absorbing fuel vapors. If it becomes saturated or clogged, it restricts the flow of vapor.
2. Blocked or Pinched EVAP Lines: Check the hoses and lines connecting the charcoal canister, purge valve, and intake manifold for kinks, pinches, or blockages. A rodent could have chewed through a line, or a hose may have simply come loose.
3. Faulty Purge Valve (VSV): While the duty cycle reading indicates the valve is opening and closing as commanded, it may not be opening wide enough or could be internally blocked, preventing sufficient flow.
4. Faulty Vent Valve: The vent valve controls the flow of air into the canister during purging. If it malfunctions and remains closed, it can create a vacuum and prevent vapor flow.
5. Clogged Canister Vent: A blockage in the vent line leading to the canister will have the same effect as a faulty vent valve.
6. Other Restrictions: There could be other, less common restrictions within the EVAP system, such as a clogged filter or a blocked orifice in the intake manifold.

Important Note: In some cases, a low purge flow might be a normal condition under certain driving conditions (e.g., idling). However, if it persists across different conditions, it's important to diagnose and resolve the underlying issue.

Troubleshooting Tips:

• Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to see if any EVAP-related codes have been stored. These can provide valuable clues about the source of the problem.
• Inspect Visually: Carefully examine all EVAP components and hoses for any signs of damage, leaks, or blockages.
• Test the Purge Valve: You can often test the purge valve by applying vacuum or voltage directly to it and listening for a clicking sound or checking for vapor flow. Consult your vehicle's service manual for specific instructions.
• Consider Professional Diagnosis: If you're not comfortable troubleshooting the EVAP system yourself, it's best to have a qualified mechanic diagnose and repair the issue.

My Charcoal Canister was replaced in October and the Vent Valve was replaced yesterday...

In that case, we need to look beyond the charcoal canister and vent valve for the cause of the low purge flow. Since those components were recently replaced, it's unlikely they're the culprit unless there was an issue with the installation or a faulty replacement part. Here are some additional possibilities:

1. Purge Valve (VSV): Even though the duty cycle reading suggests it's functioning, it's worth double-checking the purge valve. It could be opening partially due to debris or a mechanical fault. Try testing it by applying vacuum or voltage directly, as outlined in your vehicle's service manual.
2. EVAP System Leaks: A leak anywhere in the EVAP system could cause a loss of vacuum and reduce purge flow. Inspect all hoses, connections, and the gas cap for cracks, loose fittings, or signs of damage.
3. Wiring and Electrical Connections: Check the wiring harness and connectors associated with the purge valve, vent valve, and pressure sensor for corrosion, damage, or loose connections. A faulty electrical connection could prevent the purge valve from opening fully.
4. Pressure Sensor: A malfunctioning pressure sensor could provide inaccurate readings to the ECM, leading to incorrect purge commands. Consider having the sensor tested if other potential issues are ruled out.
5. Software Glitch: In rare cases, a software glitch in the ECM could cause issues with EVAP system control. Check for any available software updates from the manufacturer.
   
   

Would any of this cause fuel "boiling" in the gas tank and vapors exiting the fuel filler area? What role would ambient temperatures or altitude play in this?


Yes, absolutely! The issues we've been discussing could definitely contribute to fuel boiling and vapor venting from the fuel filler area, especially when combined with high ambient temperatures or altitude.
How it Happens:

1. Increased Pressure: A blockage in the EVAP system prevents fuel vapors from being purged. As the fuel warms up (from driving or hot weather), these vapors build up pressure in the fuel tank.
2. Boiling Point Reduction: Higher altitudes mean lower atmospheric pressure. This, combined with increased pressure in the tank, can lower the boiling point of the fuel, making it more likely to vaporize.
3. Vapor Expansion: As the fuel vaporizes, it expands, further increasing pressure within the fuel tank.
4. Venting: The excess pressure forces fuel vapors out through the path of least resistance, often the fuel filler cap or a vent hose. You might notice a strong fuel smell or even see liquid fuel spitting out in extreme cases.

The Role of Temperature and Altitude:

• Temperature: Hot weather exacerbates the problem because it increases fuel temperature and the rate of vaporization. This is why fuel boiling and venting are more common in summer or in hot climates.
• Altitude: Higher altitudes, with their lower atmospheric pressure, lower the fuel's boiling point, making it easier for the fuel to vaporize and create pressure in the tank.

Other Contributing Factors:
Besides the EVAP system issues we've discussed, other factors can contribute to fuel boiling:

• Low Fuel Level: A low fuel level leaves more space in the tank for vapor to accumulate and pressure to build.
• Fuel Composition: Some fuels are more prone to vaporization than others.

Addressing the Issue:
To resolve this problem, you'll need to address the root cause of the EVAP system blockage. Once the purge flow is restored, the system should be able to vent excess vapors properly, preventing pressure buildup and fuel boiling.
It's also a good idea to check the condition of your fuel filler cap and ensure it's sealing properly. A faulty cap could contribute to pressure buildup or allow vapors to escape.
If you're frequently driving at high altitudes or in hot weather, you might consider:

• Keeping the Fuel Tank Fuller: This leaves less space for vapor to accumulate.
• Parking in the Shade: This helps keep fuel temperatures lower.
• Using a Fuel Additive: Some fuel additives claim to reduce vapor pressure and can help prevent boiling.

Well, its a brave new world...

 

[isthatalexus]

Okay decided to log some data and then asked Gemini what it means and I think I found part of the problem:

I tracked the following during a 5pm drive in 113f heat alternating between surface streets and freeways:

1. Command evaporative purge: Bounced between 0% and 100%
2. Evap (Purge) VSV: Almost always matched "Command evaporative purge"
3. EVAP Purge Flow: never saw it higher than 6.5%

According to Gemini, in a system working correctly the three metrics should have tracked relatively close to each other:

Absolutely! Let's break down the relationship between these EVAP (Evaporative Emission Control) system metrics:

Commanded Evaporative Purge (%)

• What it is: This is the target or desired amount of fuel vapor purging that the engine control module (ECM) wants to achieve. The ECM calculates this based on factors like engine load, temperature, and driving conditions.
• Why it matters: It sets the goal for how much fuel vapor should be pulled from the charcoal canister and into the engine for combustion. This helps reduce emissions and improve fuel efficiency.

Evap (Purge) VSV (%)

• What it is: This is the duty cycle (the percentage of time it's open) of the purge control solenoid valve. This valve is the gatekeeper that regulates the flow of fuel vapor from the charcoal canister to the intake manifold.
• Why it matters: The ECM controls the Evap (Purge) VSV to match the Commanded Evaporative Purge as closely as possible. A higher duty cycle means more vapor is being purged.

EVAP Purge Flow (%)

• What it is: This is the actual amount of fuel vapor being purged, often expressed as a percentage of the maximum flow rate the system is designed for.
• Why it matters: It shows how effectively the system is removing fuel vapor from the charcoal canister. Ideally, this should closely match the Commanded Evaporative Purge. If it doesn't, there might be a problem with the purge valve, the charcoal canister, or other components.

The Relationship

1. ECM Commands: The ECM determines the Commanded Evaporative Purge based on driving conditions.
2. VSV Opens/Closes: The ECM adjusts the duty cycle of the Evap (Purge) VSV to control the flow of vapor.
3. Vapor Flows: The EVAP Purge Flow reflects how much vapor is actually being pulled into the engine.
4. Monitoring and Adjustment: The ECM continuously monitors the EVAP Purge Flow and compares it to the Commanded Evaporative Purge. If there's a discrepancy, it adjusts the Evap (Purge) VSV to try and correct it.

Example:

• Commanded Evaporative Purge: 50%
• Evap (Purge) VSV: 48% (The valve is open 48% of the time)
• EVAP Purge Flow: 45%

In this example, the system is working fairly well, but the ECM might slightly increase the VSV duty cycle to try and get the actual purge flow closer to the commanded value.
So why would the actual be greatly lower than the 100% being asked for?
Gemini says:
If the EVAP Purge Flow is significantly lower than the commanded purge and VSV duty cycle, it indicates a restriction or blockage in the EVAP system, preventing the fuel vapor from flowing freely. Here are some common causes to investigate:

1. Clogged EVAP Canister: The charcoal canister is responsible for absorbing fuel vapors. If it becomes saturated or clogged, it restricts the flow of vapor.
2. Blocked or Pinched EVAP Lines: Check the hoses and lines connecting the charcoal canister, purge valve, and intake manifold for kinks, pinches, or blockages. A rodent could have chewed through a line, or a hose may have simply come loose.
3. Faulty Purge Valve (VSV): While the duty cycle reading indicates the valve is opening and closing as commanded, it may not be opening wide enough or could be internally blocked, preventing sufficient flow.
4. Faulty Vent Valve: The vent valve controls the flow of air into the canister during purging. If it malfunctions and remains closed, it can create a vacuum and prevent vapor flow.
5. Clogged Canister Vent: A blockage in the vent line leading to the canister will have the same effect as a faulty vent valve.
6. Other Restrictions: There could be other, less common restrictions within the EVAP system, such as a clogged filter or a blocked orifice in the intake manifold.

Important Note: In some cases, a low purge flow might be a normal condition under certain driving conditions (e.g., idling). However, if it persists across different conditions, it's important to diagnose and resolve the underlying issue.

Troubleshooting Tips:

• Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to see if any EVAP-related codes have been stored. These can provide valuable clues about the source of the problem.
• Inspect Visually: Carefully examine all EVAP components and hoses for any signs of damage, leaks, or blockages.
• Test the Purge Valve: You can often test the purge valve by applying vacuum or voltage directly to it and listening for a clicking sound or checking for vapor flow. Consult your vehicle's service manual for specific instructions.
• Consider Professional Diagnosis: If you're not comfortable troubleshooting the EVAP system yourself, it's best to have a qualified mechanic diagnose and repair the issue.

My Charcoal Canister was replaced in October and the Vent Valve was replaced yesterday...

In that case, we need to look beyond the charcoal canister and vent valve for the cause of the low purge flow. Since those components were recently replaced, it's unlikely they're the culprit unless there was an issue with the installation or a faulty replacement part. Here are some additional possibilities:

1. Purge Valve (VSV): Even though the duty cycle reading suggests it's functioning, it's worth double-checking the purge valve. It could be opening partially due to debris or a mechanical fault. Try testing it by applying vacuum or voltage directly, as outlined in your vehicle's service manual.
2. EVAP System Leaks: A leak anywhere in the EVAP system could cause a loss of vacuum and reduce purge flow. Inspect all hoses, connections, and the gas cap for cracks, loose fittings, or signs of damage.
3. Wiring and Electrical Connections: Check the wiring harness and connectors associated with the purge valve, vent valve, and pressure sensor for corrosion, damage, or loose connections. A faulty electrical connection could prevent the purge valve from opening fully.
4. Pressure Sensor: A malfunctioning pressure sensor could provide inaccurate readings to the ECM, leading to incorrect purge commands. Consider having the sensor tested if other potential issues are ruled out.
5. Software Glitch: In rare cases, a software glitch in the ECM could cause issues with EVAP system control. Check for any available software updates from the manufacturer.
   

Would any of this cause fuel "boiling" in the gas tank and vapors exiting the fuel filler area? What role would ambient temperatures or altitude play in this?


Yes, absolutely! The issues we've been discussing could definitely contribute to fuel boiling and vapor venting from the fuel filler area, especially when combined with high ambient temperatures or altitude.
How it Happens:

1. Increased Pressure: A blockage in the EVAP system prevents fuel vapors from being purged. As the fuel warms up (from driving or hot weather), these vapors build up pressure in the fuel tank.
2. Boiling Point Reduction: Higher altitudes mean lower atmospheric pressure. This, combined with increased pressure in the tank, can lower the boiling point of the fuel, making it more likely to vaporize.
3. Vapor Expansion: As the fuel vaporizes, it expands, further increasing pressure within the fuel tank.
4. Venting: The excess pressure forces fuel vapors out through the path of least resistance, often the fuel filler cap or a vent hose. You might notice a strong fuel smell or even see liquid fuel spitting out in extreme cases.

The Role of Temperature and Altitude:

• Temperature: Hot weather exacerbates the problem because it increases fuel temperature and the rate of vaporization. This is why fuel boiling and venting are more common in summer or in hot climates.
• Altitude: Higher altitudes, with their lower atmospheric pressure, lower the fuel's boiling point, making it easier for the fuel to vaporize and create pressure in the tank.

Other Contributing Factors:
Besides the EVAP system issues we've discussed, other factors can contribute to fuel boiling:

• Low Fuel Level: A low fuel level leaves more space in the tank for vapor to accumulate and pressure to build.
• Fuel Composition: Some fuels are more prone to vaporization than others.

Addressing the Issue:
To resolve this problem, you'll need to address the root cause of the EVAP system blockage. Once the purge flow is restored, the system should be able to vent excess vapors properly, preventing pressure buildup and fuel boiling.
It's also a good idea to check the condition of your fuel filler cap and ensure it's sealing properly. A faulty cap could contribute to pressure buildup or allow vapors to escape.
If you're frequently driving at high altitudes or in hot weather, you might consider:

• Keeping the Fuel Tank Fuller: This leaves less space for vapor to accumulate.
• Parking in the Shade: This helps keep fuel temperatures lower.
• Using a Fuel Additive: Some fuel additives claim to reduce vapor pressure and can help prevent boiling.

Well, its a brave new world...

Respect. Gemini throwing down. Awesome.

So, where you looking for the blockage? You do not have LRA on this truck, right? Among other things, I had a pinched harness between LRA and frame rails (you probably don't have that since no LRA), and I found one of the pins on my old CC connectors bent at 90 deg (i.e., no contact). Physical tank or line damage?

And LOL about 'check fuel cap' comment. Even Gemini knows. I'm surprised it didn't recommend checking battery.

 

[TheGrrrrr]

Respect. Gemini throwing down. Awesome.

So, where you looking for the blockage? You do not have LRA on this truck, right? Among other things, I had a pinched harness between LRA and frame rails (you probably don't have that since no LRA), and I found one of the pins on my old CC connectors bent at 90 deg (i.e., no contact). Physical tank or line damage?

And LOL about 'check fuel cap' comment. Even Gemini knows. I'm surprised it didn't recommend checking battery.

First I'm replacing these bits to eliminate any function parts that could play a role. At that point the VSV/CC/Vent will all be new. Then I'll evaluate the wiring to both as well as to the CC. Then I'll start looking for blockages in lines. My goal is to get the EVAP Purge Flow % in line with what is being asked for. Once that has been accomplished, I'll go back to evaluating sources/mitigations of heat. I don't think there is a magic bullet on this.

 

[isthatalexus]

First I'm replacing these bits to eliminate any function parts that could play a role. At that point the VSV/CC/Vent will all be new. Then I'll evaluate the wiring to both as well as to the CC. Then I'll start looking for blockages in lines. My goal is to get the EVAP Purge Flow % in line with what is being asked for. Once that has been accomplished, I'll go back to evaluating sources/mitigations of heat. I don't think there is a magic bullet on this.

View attachment 3686360

I asked Reactor about both of these, it responded:

It is worth noting that some Toyota Land Cruiser models may not have a dedicated EVAP Purge Flow sensor. Instead, they may use other sensors, such as the fuel tank pressure sensor or the manifold absolute pressure sensor, to estimate purge flow rates and diagnose issues with the EVAP system.

This reminded me that I also replaced the fuel pump during my adventures in EVAP system. Unfortunately, I did not do all of these things one at a time, due to reasons and general frustration, but the pump was in the mix. There is a pump recall right around 2008 (my model) for the Tundra IIRC. It gets weak due to wear on the impeller and sends fuel trims to the moon. Finally, a careful radiator cleaning cleared up all the issues. Multiple factors were in play for me.

 

[linuxgod]

Okay decided to log some data and then asked Gemini what it means and I think I found part of the problem:

I tracked the following during a 5pm drive in 113f heat alternating between surface streets and freeways:

1. Command evaporative purge: Bounced between 0% and 100%
2. Evap (Purge) VSV: Almost always matched "Command evaporative purge"
3. EVAP Purge Flow: never saw it higher than 6.5%

According to Gemini, in a system working correctly the three metrics should have tracked relatively close to each other:

Absolutely! Let's break down the relationship between these EVAP (Evaporative Emission Control) system metrics:

Commanded Evaporative Purge (%)

• What it is: This is the target or desired amount of fuel vapor purging that the engine control module (ECM) wants to achieve. The ECM calculates this based on factors like engine load, temperature, and driving conditions.
• Why it matters: It sets the goal for how much fuel vapor should be pulled from the charcoal canister and into the engine for combustion. This helps reduce emissions and improve fuel efficiency.

Evap (Purge) VSV (%)

• What it is: This is the duty cycle (the percentage of time it's open) of the purge control solenoid valve. This valve is the gatekeeper that regulates the flow of fuel vapor from the charcoal canister to the intake manifold.
• Why it matters: The ECM controls the Evap (Purge) VSV to match the Commanded Evaporative Purge as closely as possible. A higher duty cycle means more vapor is being purged.

EVAP Purge Flow (%)

• What it is: This is the actual amount of fuel vapor being purged, often expressed as a percentage of the maximum flow rate the system is designed for.
• Why it matters: It shows how effectively the system is removing fuel vapor from the charcoal canister. Ideally, this should closely match the Commanded Evaporative Purge. If it doesn't, there might be a problem with the purge valve, the charcoal canister, or other components.

The Relationship

1. ECM Commands: The ECM determines the Commanded Evaporative Purge based on driving conditions.
2. VSV Opens/Closes: The ECM adjusts the duty cycle of the Evap (Purge) VSV to control the flow of vapor.
3. Vapor Flows: The EVAP Purge Flow reflects how much vapor is actually being pulled into the engine.
4. Monitoring and Adjustment: The ECM continuously monitors the EVAP Purge Flow and compares it to the Commanded Evaporative Purge. If there's a discrepancy, it adjusts the Evap (Purge) VSV to try and correct it.

Example:

• Commanded Evaporative Purge: 50%
• Evap (Purge) VSV: 48% (The valve is open 48% of the time)
• EVAP Purge Flow: 45%

In this example, the system is working fairly well, but the ECM might slightly increase the VSV duty cycle to try and get the actual purge flow closer to the commanded value.
So why would the actual be greatly lower than the 100% being asked for?
Gemini says:
If the EVAP Purge Flow is significantly lower than the commanded purge and VSV duty cycle, it indicates a restriction or blockage in the EVAP system, preventing the fuel vapor from flowing freely. Here are some common causes to investigate:

1. Clogged EVAP Canister: The charcoal canister is responsible for absorbing fuel vapors. If it becomes saturated or clogged, it restricts the flow of vapor.
2. Blocked or Pinched EVAP Lines: Check the hoses and lines connecting the charcoal canister, purge valve, and intake manifold for kinks, pinches, or blockages. A rodent could have chewed through a line, or a hose may have simply come loose.
3. Faulty Purge Valve (VSV): While the duty cycle reading indicates the valve is opening and closing as commanded, it may not be opening wide enough or could be internally blocked, preventing sufficient flow.
4. Faulty Vent Valve: The vent valve controls the flow of air into the canister during purging. If it malfunctions and remains closed, it can create a vacuum and prevent vapor flow.
5. Clogged Canister Vent: A blockage in the vent line leading to the canister will have the same effect as a faulty vent valve.
6. Other Restrictions: There could be other, less common restrictions within the EVAP system, such as a clogged filter or a blocked orifice in the intake manifold.

Important Note: In some cases, a low purge flow might be a normal condition under certain driving conditions (e.g., idling). However, if it persists across different conditions, it's important to diagnose and resolve the underlying issue.

Troubleshooting Tips:

• Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to see if any EVAP-related codes have been stored. These can provide valuable clues about the source of the problem.
• Inspect Visually: Carefully examine all EVAP components and hoses for any signs of damage, leaks, or blockages.
• Test the Purge Valve: You can often test the purge valve by applying vacuum or voltage directly to it and listening for a clicking sound or checking for vapor flow. Consult your vehicle's service manual for specific instructions.
• Consider Professional Diagnosis: If you're not comfortable troubleshooting the EVAP system yourself, it's best to have a qualified mechanic diagnose and repair the issue.

My Charcoal Canister was replaced in October and the Vent Valve was replaced yesterday...

In that case, we need to look beyond the charcoal canister and vent valve for the cause of the low purge flow. Since those components were recently replaced, it's unlikely they're the culprit unless there was an issue with the installation or a faulty replacement part. Here are some additional possibilities:

1. Purge Valve (VSV): Even though the duty cycle reading suggests it's functioning, it's worth double-checking the purge valve. It could be opening partially due to debris or a mechanical fault. Try testing it by applying vacuum or voltage directly, as outlined in your vehicle's service manual.
2. EVAP System Leaks: A leak anywhere in the EVAP system could cause a loss of vacuum and reduce purge flow. Inspect all hoses, connections, and the gas cap for cracks, loose fittings, or signs of damage.
3. Wiring and Electrical Connections: Check the wiring harness and connectors associated with the purge valve, vent valve, and pressure sensor for corrosion, damage, or loose connections. A faulty electrical connection could prevent the purge valve from opening fully.
4. Pressure Sensor: A malfunctioning pressure sensor could provide inaccurate readings to the ECM, leading to incorrect purge commands. Consider having the sensor tested if other potential issues are ruled out.
5. Software Glitch: In rare cases, a software glitch in the ECM could cause issues with EVAP system control. Check for any available software updates from the manufacturer.
   

Would any of this cause fuel "boiling" in the gas tank and vapors exiting the fuel filler area? What role would ambient temperatures or altitude play in this?


Yes, absolutely! The issues we've been discussing could definitely contribute to fuel boiling and vapor venting from the fuel filler area, especially when combined with high ambient temperatures or altitude.
How it Happens:

1. Increased Pressure: A blockage in the EVAP system prevents fuel vapors from being purged. As the fuel warms up (from driving or hot weather), these vapors build up pressure in the fuel tank.
2. Boiling Point Reduction: Higher altitudes mean lower atmospheric pressure. This, combined with increased pressure in the tank, can lower the boiling point of the fuel, making it more likely to vaporize.
3. Vapor Expansion: As the fuel vaporizes, it expands, further increasing pressure within the fuel tank.
4. Venting: The excess pressure forces fuel vapors out through the path of least resistance, often the fuel filler cap or a vent hose. You might notice a strong fuel smell or even see liquid fuel spitting out in extreme cases.

The Role of Temperature and Altitude:

• Temperature: Hot weather exacerbates the problem because it increases fuel temperature and the rate of vaporization. This is why fuel boiling and venting are more common in summer or in hot climates.
• Altitude: Higher altitudes, with their lower atmospheric pressure, lower the fuel's boiling point, making it easier for the fuel to vaporize and create pressure in the tank.

Other Contributing Factors:
Besides the EVAP system issues we've discussed, other factors can contribute to fuel boiling:

• Low Fuel Level: A low fuel level leaves more space in the tank for vapor to accumulate and pressure to build.
• Fuel Composition: Some fuels are more prone to vaporization than others.

Addressing the Issue:
To resolve this problem, you'll need to address the root cause of the EVAP system blockage. Once the purge flow is restored, the system should be able to vent excess vapors properly, preventing pressure buildup and fuel boiling.
It's also a good idea to check the condition of your fuel filler cap and ensure it's sealing properly. A faulty cap could contribute to pressure buildup or allow vapors to escape.
If you're frequently driving at high altitudes or in hot weather, you might consider:

• Keeping the Fuel Tank Fuller: This leaves less space for vapor to accumulate.
• Parking in the Shade: This helps keep fuel temperatures lower.
• Using a Fuel Additive: Some fuel additives claim to reduce vapor pressure and can help prevent boiling.

Well, its a brave new world...

I just set up these parameters for my drive from Wyoming to Dinosaur, UT. My evap purge flow is also basically 0, occasionally 1%, or very very rarely 2%. Photo below. While my truck seemed to sometimes have the first two values below 100%, or sometimes 0, it spent a LOT of time with both at 100% and the evap vsv purge on. Is that good or bad, I can’t say. Over a 3 or 4 hour period one time I saw the system vent valve turn on for a second.

It would be very interesting to see what a healthy trucks data is, since admittedly I got a P0441 evap code for the first time twice this week, suggesting I’m also have some sort of evap issue (and thus I don’t have a baseline and I don’t necessary trust my data is how things should be). However I don’t get boiling fuel at this time (save for Top of the World last year).

If anyone who doesn’t have a aux tank and hasn’t ever had codes can gather these metrics and record them for a few hours driving that would be awesome. It would be really helpful to know if 100% for both the commanded and actual vsv is normal operation or is a sign of something not venting correctly, especially when I see both sitting at 100% for minutes (if not 10+ minutes).

 

[TheGrrrrr]

After a 2300 mile trip, all of which would normally cause issues, I can confirm at least this much:

1. Non-ethanol fuel, no matter the octane, will not have the issue.
2. Non-ethanol fuel gained me over 1.3 mpg.
3. That’s all I can confirm, but I have further suspicions about heat soak not really being a significant part of the problem and the purge/vent function not being designed to handle ethanol fuel at altitude.

 

[bloc]

It might depend on the specific source but I have video (somewhere) of ethanol fuel boiling at the lookout near Engineer Pass in my rig.

But that’s just one anecdote.

 

[linuxgod]

After a 2300 mile trip, all of which would normally cause issues, I can confirm at least this much:

1. Non-ethanol fuel, no matter the octane, will not have the issue.
2. Non-ethanol fuel gained me over 1.3 mpg.
3. That’s all I can confirm, but I have further suspicions about heat soak not really being a significant part of the problem and the purge/vent function not being designed to handle ethanol fuel at altitude.

91 octane non-ethanol? Just asking because I’ve found I rarely need to vent my rotopax when I put 91 or 93 in it (even with ethanol) but I have to do it daily when I put in 87.

 

[TheGrrrrr]

91 octane non-ethanol? Just asking because I’ve found I rarely need to vent my rotopax when I put 91 or 93 in it (even with ethanol) but I have to do it daily when I put in 87.

Non-ethanol from 88 to 91 octane, particularly after the 2nd tank fill onward when the 10% ethanol fuel had been fully replaced/diluted, no gas smell and no boiling, no vapors.

I suspect the venting requirements of rotopax and Jerry cans would be an indicator for a given fuel composition, but I wouldn’t expect sealed container venting to be eliminated in order for target outcomes in the vehicle to be achieved.

 

[linuxgod]

Non-ethanol from 88 to 91 octane, particularly after the 2nd tank fill onward when the 10% ethanol fuel had been fully replaced/diluted, no gas smell and no boiling, no vapors.

I suspect the venting requirements of rotopax and Jerry cans would be an indicator for a given fuel composition, but I wouldn’t expect sealed container venting to be eliminated in order for target outcomes in the vehicle to be achieved.

Yeah. The evap system will vent to atmosphere though. I presume that’s an out-trade of preventing boiling vs too much tank pressure.

FYI fingers crossed I have not seen another P0441 code since the two I got in Wyoming. I’m attributing mine to a sh*tty old gas station and the pump overfilling my tank plus the weight of the trailer allowing fuel into the charcoal canister. That pump shut off at half full, and then kept shutting off multiple times until the tank got anywhere near full. The interesting part for you though is that my commanded and actual vsv % often held at 100% but purge flow was similarly 1-2% and only very occasionally getting up to high single digits while I was in WY/UT/CO and even sometimes on the drive home. So my evap numbers look similar to the ones you were questioning before…

 

[TheGrrrrr]

Yeah. The evap system will vent to atmosphere though. I presume that’s an out-trade of preventing boiling vs too much tank pressure.

FYI fingers crossed I have not seen another P0441 code since the two I got in Wyoming. I’m attributing mine to a sh*tty old gas station and the pump overfilling my tank plus the weight of the trailer allowing fuel into the charcoal canister. That pump shut off at half full, and then kept shutting off multiple times until the tank got anywhere near full. The interesting part for you though is that my commanded and actual vsv % often held at 100% but purge flow was similarly 1-2% and only very occasionally getting up to high single digits while I was in WY/UT/CO and even sometimes on the drive home. So my evap numbers look similar to the ones you were questioning before…

Same here on the Purge flow. Its looking like it may not be meaningful. I captured a ton of data for the entire trip and will post up the CSVs here for folks to look at. I'll try to add a column for fuel type/octane as best I can remember.

Data is here: TheGrrrrr Data Log - LCDC X

 

[skrypj]

This is becoming a serious PITA for me. Literally everywhere I drive now there is very noticeable gas fumes when we get out of the truck. I took a drive in the national forest near my house yesterday and literally every time my wife opened the door we could smell gas. We stopped at a bunch of different elevations, but it was a relatively cool day and we were generally moving pretty fast(45-60mph). This was not an instance of slow crawling on a hot day.

Later in the day I got a CEL and it was P0441.

This was with 1/2 to 5/8 of a tank of fuel. I purposefully did not fill the tank.

 

[skrypj]

Okay decided to log some data and then asked Gemini what it means and I think I found part of the problem:

I tracked the following during a 5pm drive in 113f heat alternating between surface streets and freeways:

1. Command evaporative purge: Bounced between 0% and 100%
2. Evap (Purge) VSV: Almost always matched "Command evaporative purge"
3. EVAP Purge Flow: never saw it higher than 6.5%

According to Gemini, in a system working correctly the three metrics should have tracked relatively close to each other:

Absolutely! Let's break down the relationship between these EVAP (Evaporative Emission Control) system metrics:

Commanded Evaporative Purge (%)

• What it is: This is the target or desired amount of fuel vapor purging that the engine control module (ECM) wants to achieve. The ECM calculates this based on factors like engine load, temperature, and driving conditions.
• Why it matters: It sets the goal for how much fuel vapor should be pulled from the charcoal canister and into the engine for combustion. This helps reduce emissions and improve fuel efficiency.

Evap (Purge) VSV (%)

• What it is: This is the duty cycle (the percentage of time it's open) of the purge control solenoid valve. This valve is the gatekeeper that regulates the flow of fuel vapor from the charcoal canister to the intake manifold.
• Why it matters: The ECM controls the Evap (Purge) VSV to match the Commanded Evaporative Purge as closely as possible. A higher duty cycle means more vapor is being purged.

EVAP Purge Flow (%)

• What it is: This is the actual amount of fuel vapor being purged, often expressed as a percentage of the maximum flow rate the system is designed for.
• Why it matters: It shows how effectively the system is removing fuel vapor from the charcoal canister. Ideally, this should closely match the Commanded Evaporative Purge. If it doesn't, there might be a problem with the purge valve, the charcoal canister, or other components.

The Relationship

1. ECM Commands: The ECM determines the Commanded Evaporative Purge based on driving conditions.
2. VSV Opens/Closes: The ECM adjusts the duty cycle of the Evap (Purge) VSV to control the flow of vapor.
3. Vapor Flows: The EVAP Purge Flow reflects how much vapor is actually being pulled into the engine.
4. Monitoring and Adjustment: The ECM continuously monitors the EVAP Purge Flow and compares it to the Commanded Evaporative Purge. If there's a discrepancy, it adjusts the Evap (Purge) VSV to try and correct it.

Example:

• Commanded Evaporative Purge: 50%
• Evap (Purge) VSV: 48% (The valve is open 48% of the time)
• EVAP Purge Flow: 45%

In this example, the system is working fairly well, but the ECM might slightly increase the VSV duty cycle to try and get the actual purge flow closer to the commanded value.
So why would the actual be greatly lower than the 100% being asked for?
Gemini says:
If the EVAP Purge Flow is significantly lower than the commanded purge and VSV duty cycle, it indicates a restriction or blockage in the EVAP system, preventing the fuel vapor from flowing freely. Here are some common causes to investigate:

1. Clogged EVAP Canister: The charcoal canister is responsible for absorbing fuel vapors. If it becomes saturated or clogged, it restricts the flow of vapor.
2. Blocked or Pinched EVAP Lines: Check the hoses and lines connecting the charcoal canister, purge valve, and intake manifold for kinks, pinches, or blockages. A rodent could have chewed through a line, or a hose may have simply come loose.
3. Faulty Purge Valve (VSV): While the duty cycle reading indicates the valve is opening and closing as commanded, it may not be opening wide enough or could be internally blocked, preventing sufficient flow.
4. Faulty Vent Valve: The vent valve controls the flow of air into the canister during purging. If it malfunctions and remains closed, it can create a vacuum and prevent vapor flow.
5. Clogged Canister Vent: A blockage in the vent line leading to the canister will have the same effect as a faulty vent valve.
6. Other Restrictions: There could be other, less common restrictions within the EVAP system, such as a clogged filter or a blocked orifice in the intake manifold.

Important Note: In some cases, a low purge flow might be a normal condition under certain driving conditions (e.g., idling). However, if it persists across different conditions, it's important to diagnose and resolve the underlying issue.

Troubleshooting Tips:

• Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to see if any EVAP-related codes have been stored. These can provide valuable clues about the source of the problem.
• Inspect Visually: Carefully examine all EVAP components and hoses for any signs of damage, leaks, or blockages.
• Test the Purge Valve: You can often test the purge valve by applying vacuum or voltage directly to it and listening for a clicking sound or checking for vapor flow. Consult your vehicle's service manual for specific instructions.
• Consider Professional Diagnosis: If you're not comfortable troubleshooting the EVAP system yourself, it's best to have a qualified mechanic diagnose and repair the issue.

My Charcoal Canister was replaced in October and the Vent Valve was replaced yesterday...

In that case, we need to look beyond the charcoal canister and vent valve for the cause of the low purge flow. Since those components were recently replaced, it's unlikely they're the culprit unless there was an issue with the installation or a faulty replacement part. Here are some additional possibilities:

1. Purge Valve (VSV): Even though the duty cycle reading suggests it's functioning, it's worth double-checking the purge valve. It could be opening partially due to debris or a mechanical fault. Try testing it by applying vacuum or voltage directly, as outlined in your vehicle's service manual.
2. EVAP System Leaks: A leak anywhere in the EVAP system could cause a loss of vacuum and reduce purge flow. Inspect all hoses, connections, and the gas cap for cracks, loose fittings, or signs of damage.
3. Wiring and Electrical Connections: Check the wiring harness and connectors associated with the purge valve, vent valve, and pressure sensor for corrosion, damage, or loose connections. A faulty electrical connection could prevent the purge valve from opening fully.
4. Pressure Sensor: A malfunctioning pressure sensor could provide inaccurate readings to the ECM, leading to incorrect purge commands. Consider having the sensor tested if other potential issues are ruled out.
5. Software Glitch: In rare cases, a software glitch in the ECM could cause issues with EVAP system control. Check for any available software updates from the manufacturer.
   

Would any of this cause fuel "boiling" in the gas tank and vapors exiting the fuel filler area? What role would ambient temperatures or altitude play in this?


Yes, absolutely! The issues we've been discussing could definitely contribute to fuel boiling and vapor venting from the fuel filler area, especially when combined with high ambient temperatures or altitude.
How it Happens:

1. Increased Pressure: A blockage in the EVAP system prevents fuel vapors from being purged. As the fuel warms up (from driving or hot weather), these vapors build up pressure in the fuel tank.
2. Boiling Point Reduction: Higher altitudes mean lower atmospheric pressure. This, combined with increased pressure in the tank, can lower the boiling point of the fuel, making it more likely to vaporize.
3. Vapor Expansion: As the fuel vaporizes, it expands, further increasing pressure within the fuel tank.
4. Venting: The excess pressure forces fuel vapors out through the path of least resistance, often the fuel filler cap or a vent hose. You might notice a strong fuel smell or even see liquid fuel spitting out in extreme cases.

The Role of Temperature and Altitude:

• Temperature: Hot weather exacerbates the problem because it increases fuel temperature and the rate of vaporization. This is why fuel boiling and venting are more common in summer or in hot climates.
• Altitude: Higher altitudes, with their lower atmospheric pressure, lower the fuel's boiling point, making it easier for the fuel to vaporize and create pressure in the tank.

Other Contributing Factors:
Besides the EVAP system issues we've discussed, other factors can contribute to fuel boiling:

• Low Fuel Level: A low fuel level leaves more space in the tank for vapor to accumulate and pressure to build.
• Fuel Composition: Some fuels are more prone to vaporization than others.

Addressing the Issue:
To resolve this problem, you'll need to address the root cause of the EVAP system blockage. Once the purge flow is restored, the system should be able to vent excess vapors properly, preventing pressure buildup and fuel boiling.
It's also a good idea to check the condition of your fuel filler cap and ensure it's sealing properly. A faulty cap could contribute to pressure buildup or allow vapors to escape.
If you're frequently driving at high altitudes or in hot weather, you might consider:

• Keeping the Fuel Tank Fuller: This leaves less space for vapor to accumulate.
• Parking in the Shade: This helps keep fuel temperatures lower.
• Using a Fuel Additive: Some fuel additives claim to reduce vapor pressure and can help prevent boiling.

Well, its a brave new world...

Why would keeping the tank fuller be better? Wouldnt that mean you need less fuel to boil before the remaining volume in the tank is pressurized enough to cause venting?

 

[2001LC]

You'll need to run diagnostic on EVAP system. Likely you'll need a new Charcoal canister.

But first make sure radiator fins cleaned clear of debris, no vacuum leaks, coolant system & engine, along with A/T. All running at peak performance!.

Then never add more fuel, after auto shut off of filling station handle.
Never top more than 7/8 of tank on hot day, if: Parking or climb or rock road.

 

[TheGrrrrr]

Why would keeping the tank fuller be better? Wouldnt that mean you need less fuel to boil before the remaining volume in the tank is pressurized enough to cause venting?

Takes more heat/time to boil 20 gallons of fuel than it does 10 gallons. My guess is your charcoal canister is shot, which is making it worse. Replace it and you’ll probably buy yourself more margin. The key is using ethanol free if you can find it.

 

[TeCKis300]

This is becoming a serious PITA for me. Literally everywhere I drive now there is very noticeable gas fumes when we get out of the truck. I took a drive in the national forest near my house yesterday and literally every time my wife opened the door we could smell gas. We stopped at a bunch of different elevations, but it was a relatively cool day and we were generally moving pretty fast(45-60mph). This was not an instance of slow crawling on a hot day.

Later in the day I got a CEL and it was P0441.

This was with 1/2 to 5/8 of a tank of fuel. I purposefully did not fill the tank.

IIRC, you have Victory skids? Get rid of them. They had the same issue when they were developing and testing their skids and evidently didn't bother to iterate sufficiently. It was so bad, they had to remove their skids mid-test. Honestly, most skids are going to trap heat and increase fuel heating to some degree.

On a separate note, I seem to have some measure of improvement with fuel boiling. Between adding insulation to the fuel lines and gas tank especially where they come close to the hot exhaust. Also added a body lift which probably improves airflow and trapping of heat in the chassis. Recently returned to Big Bear White Mountain at 8k ft in the summer, which is where I had problems with some mild fuel vapers previously. No issue to speak of this time. Can't say it's permanently solved to higher elevations and hotter temps, as this problem is all about margin and degree of. But seems better.