Gas tank building excessive pressure & fuel smell. Dangerous for sure! Why does this happen?

[abuck99]

Agree with the heat shielding. I have an LRA 40 gal tank coming in August and I'm going to refresh the fuel system lines, add shields in various places. I've never had the boiling issue or overheating. But just in case

What I'm interpreting from @2001LC is that we all don't necessarily need heat shields as a corrective measure- rather getting base engine condition in order before modifying/fabricating heat shielding.

VSVs will DEFINITELY indicate working when tested but still stick. The one on the intake should be checked closely. If that one sticks, you get no vacuum on the canister at all. And again, I'll add this - check for exhaust leaks. Even a small leak is putting 500-800 degree exhaust under the truck, and will boil your fuel. It will be worse if you are towing any trailer, as well, since the trailer messes with the cooling flow of airflow under the truck.

Very interesting, good info! please expand on your experience around this and how you uncovered this.

regardless of what conversions, or numbers or units you guys get, that # from -4.1 to +2.1 is next to zero pressure. Your lungs can blow just under +4. kPa So it should be easy to just say you're over what it should be.

umm..... where is this vapor pressure sensor and how can I see it. TS reads Kpa? I've never looked. In the canister?
I'm guilty of not having a fuel smell, vapor, issue for a few years now.

I only put a shield up on the drivers side. I use to hear it boil all the time.
Seems simple to me, it gets hot, it boils, you can hear it boil, do what you got to do keep it from getting hot. MOTO

Vapor Pressure Sensor is mounted on top of the fuel tank:

 

[gatormark91]

What I'm interpreting from @2001LC is that we all don't necessarily need heat shields as a corrective measure- rather getting base engine condition in order before modifying/fabricating heat shielding.



Very interesting, good info! please expand on your experience around this and how you uncovered this.


Vapor Pressure Sensor is mounted on top of the fuel tank:
View attachment 2349894View attachment 2349901
View attachment 2349903

The VSV on the manifold is supposed to be open all the time when the engine is on, and closed when off. But since it is a fuel system part, it can get gummed up like anything else in the fuel system. So the solenoid will click on - and the ECU will read it as on -but it can still be gummed up, sticky, etc. It will still test OK even if you kick it open with Techstream, but still be no good, like mine was.

The VSV on the charcoal canister only serves to expose the evap pressure sensor to the evap system during the criteria that meets the 'LA4' emissions system self-test, as I understand it. That VSV and the evap sensor does not have anything to do with the daily function of the system, again as I understand it, through my own research. That VSV is only there to kick open when the ECU decides that the temperature and load conditions have been the same as Los Angeles traffic at 4pm ('LA4") for long enough, then it runs a self-test. This is why you'll get an intermittent evap CEL, but then won't get one again for a long time. Until the ECU ticks off what it needs to call for an LA4 emissions test, it does not set the evap CEL.

 

[DTC72]

regardless of what conversions, or numbers or units you guys get, that # from -4.1 to +2.1 is next to zero pressure. Your lungs can blow just under +4. kPa So it should be easy to just say you're over what it should be.

umm..... where is this vapor pressure sensor and how can I see it. TS reads Kpa? I've never looked. In the canister?
I'm guilty of not having a fuel smell, vapor, issue for a few years now.

I only put a shield up on the drivers side. I use to hear it boil all the time.
Seems simple to me, it gets hot, it boils, you can hear it boil, do what you got to do keep it from getting hot. MOTO

I switched my reading to kPa in BlueDriver. Tech support at BD told me that if the Absolute Evap System Pressure stays in the range 76-110 kPa then it will throw a code. My reading currently is 90.240 and no code so not sure on that data range validity. My goal here is to monitor this reading to see when I might be approaching the issue.

 

[abuck99]

The VSV on the manifold is supposed to be open all the time when the engine is on, and closed when off. But since it is a fuel system part, it can get gummed up like anything else in the fuel system. So the solenoid will click on - and the ECU will read it as on -but it can still be gummed up, sticky, etc. It will still test OK even if you kick it open with Techstream, but still be no good, like mine was.

The VSV on the charcoal canister only serves to expose the evap pressure sensor to the evap system during the criteria that meets the 'LA4' emissions system self-test, as I understand it. That VSV and the evap sensor does not have anything to do with the daily function of the system, again as I understand it, through my own research. That VSV is only there to kick open when the ECU decides that the temperature and load conditions have been the same as Los Angeles traffic at 4pm ('LA4") for long enough, then it runs a self-test. This is why you'll get an intermittent evap CEL, but then won't get one again for a long time. Until the ECU ticks off what it needs to call for an LA4 emissions test, it does not set the evap CEL.

Good info thanks- Just to confirm you're speaking about this VSV for EVAP (Valve Assy, Vacuum Switching No. 2 #25860-50100)? There is a small collector (Vacuum Surge Tank or Vacuum Reservoir I think its called) in line just an inch or two before the VSV- did you replace that and the line as well?

VSV Part number:

 

[wsudu]

Off Camber Driving at Altitude with 3/4 to full fuel tank in hot weather: my thought that running off camber at various angles, sloshing gas, warm conditions where fuel and vapors expand fuel inside tank the EVAP line gets fuel or condensation in it and cannot process vapor effectively.

For me this has always been a part of it, and I think it is an underrated consideration. I've had this happen a bunch and in fact, I had it happen last week at 900 feet in Arkansas after a long day of off roading at 84 degrees! I know all factors come into play and there are many but I've never had this happen when driving normally through on the highway even if it's 100+ degrees (Vegas to LA). I have had it happen on the highway after I had gone off roading, even in cooler temps. I just feel that it's heat related more than anything so I'm going to try the heat shield first.

 

[gatormark91]

I switched my reading to kPa in BlueDriver. Tech support at BD told me that if the Absolute Evap System Pressure stays in the range 76-110 kPa then it will throw a code. My reading currently is 90.240 and no code so not sure on that data range validity. My goal here is to monitor this reading to see when I might be approaching the issue.

The ECU only picks up higher pressure if it's doing it during a self test. Otherwise, really all the evap system does is act as little constant vac leak that sucks up fumes. The charcoal canister just collects those fumes while the engine is not running, and they get dumped to the manifold when it's on and the VSV opens. The pressure is not normally checked by the system.

 

[guardcompany]

@2001LC Sadly I've done everything in Post #2 including a new Toyota OEM radiator and still had this issue, so I don't believe it is as simple as a properly maintained cooling system. Also mine as well as some others only does it off-road. I've never had the issue on black top regardless of heat or altitude. I get it bad on a slow rocky trails in the summer with lots of back and forth movement. I just finished my heat shield and wrapping the fuel lines, doing the fuel pump next weekend and I did the pre-cat o2 sensors last month. Hopefully I'll get to doing the EVAP system before I leave for CO at the end of July, here is my parts list:

 

[87warrior]

Vapor Pressure Sensor is mounted on top of the fuel tank:
View attachment 2349894View attachment 2349901
View attachment 2349903

I assume that is for a 100 with the vapor canister above the spare. When it is under the hood the vapor pressure sensor is on the canister. Just for clarification, this is the fuel tank from my 99 and it's under hood canister:

The ECU only picks up higher pressure if it's doing it during a self test. Otherwise, really all the evap system does is act as little constant vac leak that sucks up fumes. The charcoal canister just collects those fumes while the engine is not running, and they get dumped to the manifold when it's on and the VSV opens. The pressure is not normally checked by the system.

That would also explain why an EVAP leak can take a long time for the ECU to trigger a CEL. I did not know the ECU only periodically checked the EVAP pressure.

 

[2001LC]

@2001LC Sadly I've done everything in Post #2 including a new Toyota OEM radiator and still had this issue, so I don't believe it is as simple as a properly maintained cooling system. Also mine as well as some others only does it off-road. I've never had the issue on black top regardless of heat or altitude. I get it bad on a slow rocky trails in the summer with lots of back and forth movement. I just finished my heat shield and wrapping the fuel lines, doing the fuel pump next weekend and I did the pre-cat o2 sensors last month. Hopefully I'll get to doing the EVAP system before I leave for CO at the end of July, here is my parts list:

View attachment 2350257

Yeah, it's not likely that just a tune will cure all. Even in the one I'm working on now and another I did last weekend. I don't feel we've 100% corrected the issue. Gavin, the owner seem to feel we have corrected 100%. I feel we've still some work to do. I could just add a heat shield. But that's just treating a symptom.

I'm thinking, that over-heating, over time, which resulted in boiling the fuel. Has done some damage or gunk up the works, in case I'm working now.

As far as I know, no 100 series at 0 miles from factory, had this issue of fuel cap pressure under any on or off road condition, pulling any load not exceeding limits. So it is correctable, without heat shield.

This reminds me of the "D" vibration issue. I hunted for the longest time to correct. I found what "part" was making the vibration sounds. In my case roof rack was the part, some it was engine cover, spare tire carry, etc. Many said just remove that "part". But that was not what cause of the vibration that transfer vibration to the part. It was only a symptom. Fuel boiling is a symptom of one or more components not in spec.

 

[abuck99]

I assume that is for a 100 with the vapor canister above the spare. When it is under the hood the vapor pressure sensor is on the canister. Just for clarification, this is the fuel tank from my 99 and it's under hood canister:
View attachment 2350249
View attachment 2350250


That would also explain why an EVAP leak can take a long time for the ECU to trigger a CEL. I did not know the ECU only periodically checked the EVAP pressure.

Yes for later model years where canister is near spare tire. Good clarification.

 

[guardcompany]

Yeah, it's not likely that just a tune will cure all. Even in the one I'm working on now and did last weekend. I don't feel we've 100% corrected the issue. Gavin, the owner seem to feel we have corrected 100%. I feel we've still some work to do. I could just add a heat shield. But that's just treating a symptom.

I'm thinking, that over-heating, over time, which resulted in boiling the fuel. Has done some damage or gunk up the works, in case I'm working now.

As far as I know, no 100 series at 0 miles from factory, had this issue of fuel cap pressure under any on or off road condition, pulling any load not exceeding limits. So it is correctable, without heat shield.

This reminds me of the "D" vibration issue. I hunted for the longest time to correct. I found what "part" was making the vibration sounds. In my case roof rack was the part, some it was engine cover, spare tire carry, etc. Many said just remove that "part". But that was not what cause of the vibration that transfer vibration to the part. It was only a symptom. Fuel boiling is a symptom of one or more components not in spec.

Agreed. In in fact when I bought mine it was running hot and could have done some damage for the PO.

I've thrown a lot of money at this issue so fingers crossed that this summer it's gone. I plan on keeping it forever (giving it to my son) so I'm not too upset about replacing parts that will need to be replaced at one point anyway. Making the heat shield was kinda fun too.

 

[abuck99]

The ECU only picks up higher pressure if it's doing it during a self test. Otherwise, really all the evap system does is act as little constant vac leak that sucks up fumes. The charcoal canister just collects those fumes while the engine is not running, and they get dumped to the manifold when it's on and the VSV opens. The pressure is not normally checked by the system.

Not sure I agree with you on that quite yet. What I read in the FSM is that the Monitor Strategy for EVAP VSV, CCV, Bypass VSV, and Vapor Pressure Sensor are all operated 1x per drive cycle ("Frequency of operation"). Maybe I'm interpreting that wrong.

 

[gatormark91]

Not sure I agree with you on that quite yet. What I read in the FSM is that the Monitor Strategy for EVAP VSV, CCV, Bypass VSV, and Vapor Pressure Sensor are all operated 1x per drive cycle ("Frequency of operation"). Maybe I'm interpreting that wrong.


View attachment 2350327
View attachment 2350328

That is entirely possible. But it's not constantly monitored was my point. If it checks and the system isn't doing it right then, no CEL.

 

[wretchedfred]

Following

 

[Sykoslug]

Finally got Techstream running, performed the evap system test, now I have to figure out how to interpret the results. AFAIK no codes were noted. It appeared that all 11 steps of the test made an impact on the idling of car. Test parameters require: gas temp of 95degF max, fuel level between 1/4 and 3/4.

Also installed DIY stainless heat Shields on the DS exhaust from the down pipe to 8 inches past the Cat. That was fun

I'll have to fill up with Costco gas again and see if I can replicate the problem.

 

[gatormark91]

Good info thanks- Just to confirm you're speaking about this VSV for EVAP (Valve Assy, Vacuum Switching No. 2 #25860-50100)? There is a small collector (Vacuum Surge Tank or Vacuum Reservoir I think its called) in line just an inch or two before the VSV- did you replace that and the line as well?

VSV Part number:
View attachment 2350228

View attachment 2350236

Yes, that is the one I was referring to.

 

[DTC72]

I replaced the vapor canister on my 2006 LC100 today. $615 for the part # 77740-60450 and 30 minutes of DIY labor. The canister for my year and VIN number was recalled back in 2007 but only if three specific codes were thrown...and mine never did Throw any...but thought it worth a try to get rid of another potential issue in the vapor lock chain. To date I have now replaced the vapor canister, fuel pump, fuel filter, and gas cap. All my lines looked in very good condition but I don’t have the tools to truly check for leaks. I did notice that a small amount of fuel spilled out of one of the lines going into/out of the canister when I changed it. Does only vapor go in/out of the canister? Could this mean fuel sloshed into my canister and was a part of the problem? I am headed from Las Vegas to Silverton, CO at the end of the month to do some high elevation trails. Will let this group know the results.

 

[savirc]

so glad @2001LC is digging into this, finally thorough analysis.

 

[ZREM]

I'll throw out another anecdotal data point to add to this thread.

'98 w/190k miles, replaced charcoal canister and fuel cap in the last year chasing this down.

Last weekend I filled up with ethanol free fuel in Craig, CO then drove through Steamboat and up and over Rabbit Ears Pass - normally the combination of the elevation and towing my 4000 lb camper would lead to fuel vapors and stink. On this tank of gas, nothing. No smells, no pressure, no vapor. Same day filled up in Walden, CO with "normal" gas and had some smell and vapor at the next pass.

Also, been lurking in the 200 forum as that will likely be my next vehicle and asked about this issue with the 200s - they have it as well. Doesn't sound as severe as us 100 guys, but they get it on low mileage trucks that are barely 4-5 years old.

 

[AlpineAccess]

I'll throw out another anecdotal data point to add to this thread.

'98 w/190k miles, replaced charcoal canister and fuel cap in the last year chasing this down.

Last weekend I filled up with ethanol free fuel in Craig, CO then drove through Steamboat and up and over Rabbit Ears Pass - normally the combination of the elevation and towing my 4000 lb camper would lead to fuel vapors and stink. On this tank of gas, nothing. No smells, no pressure, no vapor. Same day filled up in Walden, CO with "normal" gas and had some smell and vapor at the next pass.

Also, been lurking in the 200 forum as that will likely be my next vehicle and asked about this issue with the 200s - they have it as well. Doesn't sound as severe as us 100 guys, but they get it on low mileage trucks that are barely 4-5 years old.

I dont have it at all on a '99, regardless of elevation, fuel, load, etc.

At 140k a fuel vapor release valve was replaced which is what I believe causes this. Will try to find the receipt.

186k now. Routinely change from 5k elevation to over 10.5. Several times a year we peak out at around 12k.