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

[vjpkrmnc]

I have been following this thread for a while now, but are most people that are having this issue coming from lower elevations?

It happened to me after a sea level fill-up, freeway through 100 degree valley, up donner pass, then flamed out at 70 mph at idle coming back down from 7000 ft. Second time (last week) we filled up at 5000', had a bunch of mid 3000s shifts at 55mph, 90-95 degrees out, and after 2.5 hours en route, it flamed out the first time we slowed to idle at 6500 (unhelpfully in natl park line). There was a sign of fuel coming out on the second one (dried in the dust). I didn't hear a pressure change on releasing the cap on either one. I watched the engine temp religiously after the second occurrence and it stayed very steady at 195 all up and down Lassen to 8500', down to 190 when descending and max'ing at 204 on high rpm/extended uphills on highway driving at 95 degrees. Not very scientific but a 10 degree F swing doesn't seem like a smoking gun in itself.

Common variables:
- 2006 LC, originated in Mexico, 120k miles, stock fuel pump, new radiator/Ts, well-maintained by PO
- fill up lowland or questionable gas station; 91 octane
- 95+ degrees out
- drive it "hard" uphill with frequent shifts to 3500 rpm
- highway speeds
- occurred when going to idle pedal position following above
- newish stock gas cap on first one; brand new OReilley brand on second
- ARB bumper+ round spotlights+ Slee front skid plate (reduced air flow?)
- AC on

 

[suprarx7nut]

Hope this is helpful information for those of you trying to fix this. Most of what you guys talk about is beyond me, so use it if you can and or PM me if you want more formation

2003 LC, 272k miles, owned since 130k, around 10 yrs. all maintaince done at stealership and heavily modified.

just finished up 7 day trip from north Alabama to silverton through Oklahoma City, Albuquerque, Durango and then silverton. As you know these rigs aren’t known for gas mileage and I stopped plenty of times this trip. No issues until I got to Durango with <1/4 tank gas, 81 degrees according to LC. Got to tractor supply and from video you can hear it lightly boiling. See video. No other issues rest of week

Next 7 days are from silverton to SLC and up to Montana. In Thompson spring UT, <1/2 tank of gas, 102 outside and wow was it boiling good! Let it rest for 10 mins and it was still boiling. Took a chance and opened gas cap and stopped boiling within 30 seconds. see video

I do have a scangauge running, water temp if it matters never exceeded 193 entire trip.

I'm not sure if Scangauge can pull it, but the torque app can pull up the Evap duty cycle with a Toyota EX plugin. I think that's a valuable tool in this conversation. I've started watching my evap duty cycle and notice there can be prolonged periods where it's 0% - IE slow rolling, slow light braking.

I have been following this thread for a while now, but are most people that are having this issue coming from lower elevations?

I've had it occur with two different models (99 and 06) and in both cases, I started in Denver elevation and climbed to ~8k-10k ft. I think there are many folks seeing this problem that started at a "high" elevation so we can probably rule out low elevations only.

 

[JaromT]

The radiator is clean. The rig has never even come close to overheating as far as engine temp per the gage. Never even gone over the center line and is usually if not always a bit below the center for temp. What would a vacuum leak or loose spark plugs do? If it would cause overheating thats not happening. Truck runs great. Only has issues when it gets super hot (115+) in the afternoon then fuel tank starts to get pressurized and smell of gas comes into the cab from the charcoal filter area. I've loosened the gas cap slightly now for a day and so far no smell. I just filled up and its getting to be afternoon so I will check in again later with any updates. Thanks for any imput!!!

By the way

This would happen to me every year with my last rig, 1998 Land Cruiser. Had it for 9 years from 105K Miles to 340K miles. Never happened in winter, spring, or fall. Identical issues in summer. It can't be coincidence that it happened to each rig. Gonna try the heat shielding at the gas tank and cat. I've had the 02 LC now for 3.5 years and have gone from 39K miles to 97K miles. Smell happened in summer when it was in the 40K range the first summer I had it.

 

[yackowski]

I drove from East Texas to Lake City Colorado on Sunday. I had missed these threads apparently because I was on here searching when I arrived lol. I was pulling a 4 seat razr so she was working plenty hard the entire trip and I got to fill up often but the first time I had it happen was in Raton, NM at a little elevation. Solid fumes escaping above the cab and my head. Took probably 30 seconds before I could even get the gas pump started. Startled me to say the least. I haven’t had it happen again since if unhooked from the trailer. Even after a decent 4Lo excursion to a hiking trailhead. That’s been my experience anyway. I haven’t owned it long. After reading this I really haven’t seen a great answer to the issue. I guess I’ll just ignore it like the guy above and thank God I don’t smoke for now.

Cole

 

[Asanka]

but the torque app can pull up the Evap duty cycle with a Toyota EX plugin. I think that's a valuable tool

What engine did you select in the plugin? It doesn't list 4.7 v8

 

[suprarx7nut]

What engine did you select in the plugin? It doesn't list 4.7 v8

On the LT plugin I have Avensis (T270) selected and for EX plugin I have Corolla E140/150 selected.

I don't think it matters. I didn't see much difference with any of them. The variances between those models don't seem to produce any different data for the 2UZ. I verified the Evap duty cycle was working as well as I can tell because you can watch the duty cycle click on and off along with the idle increase cycles.

My car is an 06 LX, in case that makes any difference (I doubt it).

 

[Asanka]

On the LT plugin I have Avensis (T270) selected and for EX plugin I have Corolla E140/150 selected.

I don't think it matters. I didn't see much difference with any of them. The variances between those models don't seem to produce any different data for the 2UZ. I verified the Evap duty cycle was working as well as I can tell because you can watch the duty cycle click on and off along with the idle increase cycles.

My car is an 06 LX, in case that makes any difference (I doubt it).

Thanks, mine is non vvt (04). Will give a try

 

[vjpkrmnc]

By the way

This would happen to me every year with my last rig, 1998 Land Cruiser. Had it for 9 years from 105K Miles to 340K miles. Never happened in winter, spring, or fall. Identical issues in summer. It can't be coincidence that it happened to each rig. Gonna try the heat shielding at the gas tank and cat. I've had the 02 LC now for 3.5 years and have gone from 39K miles to 97K miles. Smell happened in summer when it was in the 40K range the first summer I had it.

Dumb question? Which heat shield? Like a DEI-type exhaust wrap? or an actual metal shield? stick a reflective sheet to the fuel tank? or wrap the fuel lines with something reflective (I saw some reflective/velcro DEI wrap at Oreilley's today).

 

[Jerzywerzy5]

My 03 has boiled over onto the quarter panel. Always at altitude going up in 4l.

 

[JaromT]

Dumb question? Which heat shield? Like a DEI-type exhaust wrap? or an actual metal shield? stick a reflective sheet to the fuel tank? or wrap the fuel lines with something reflective (I saw some reflective/velcro DEI wrap at Oreilley's today).

From J1000 who sent me this link



I recommend just doing the 4 things I list in this post in the order they are listed: Gas tank building excessive pressure & fuel smell. Dangerous for sure! Why does this happen? - https://forum.ih8mud.com/threads/gas-tank-building-excessive-pressure-fuel-smell-dangerous-for-sure-why-does-this-happen.1214321/page-11#post-13251496

Yes it is still working great for me haven't had any of the issues since.

 

[vjpkrmnc]

From J1000 who sent me this link



I recommend just doing the 4 things I list in this post in the order they are listed: Gas tank building excessive pressure & fuel smell. Dangerous for sure! Why does this happen? - https://forum.ih8mud.com/threads/gas-tank-building-excessive-pressure-fuel-smell-dangerous-for-sure-why-does-this-happen.1214321/page-11#post-13251496

Yes it is still working great for me haven't had any of the issues since.

Thanks. And thanks to @J1000. Post #206 is on my to-do list. It's a great shopping list too.

@J1000, in watching fuel temps, did you confirm a temp/altitude when boiling happened or temp had effect on the fuel pump? Like say I was to do none of your steps beyond installing a temp probe, would it be possible to then reliably avoid boiling/heat soak/flameout problems just by shutting down for a bit before getting to that point?

 

[JaromT]

Dumb question? Which heat shield? Like a DEI-type exhaust wrap? or an actual metal shield? stick a reflective sheet to the fuel tank? or wrap the fuel lines with something reflective (I saw some reflective/velcro DEI wrap at Oreilley's today).

In J1000's write up he has links to amazon with the heat shield and other items that he used. That is where I bought the heat shield - On Amazon.

 

[mfaisaln]

I don’t know how any of you guys haven’t thought of the purge valve I mean the vsv vacuum switching valve electrical connection the vsv can be functioning correctly but what if it’s not receiving the electrical signal to do so in my lx470 02 everything functions except in the wiring for the vsv the ground from the ecu is seems to be cut somehow so any idea ?

 

[vjpkrmnc]

New radiator have all the foam?

Exhaust: On my own 06LX, I believe I have exhaust leaks on the manifold (either at the head or right after header). I believe these leaks add to heat in the engine bay and therefore fuel lines/fuel. That's why I ask.

Also, FWIW, I think there are two separate issues being discussed here. They may have some overlapping causes and fixes, but they're different problems and don't necessarily occur together.

Fuel Vapor Purge failure: fuel gushing out of the filler neck because the tank is over-pressurized. Potentially deadly and known to literally burn 100's to the ground.
Hot Start Failure: Car intermittently fails to start when hot and starts again once cool.

The third one would be flameout while driving (which then leads to #2). Happened to me at 70 mph on the freeway, and again blocking the entrance line to a national park.

 

[vjpkrmnc]

I'm not sure if Scangauge can pull it, but the torque app can pull up the Evap duty cycle with a Toyota EX plugin. I think that's a valuable tool in this conversation. I've started watching my evap duty cycle and notice there can be prolonged periods where it's 0% - IE slow rolling, slow light braking.

Would that be the same as "commanded evaporative purge" (%) on my OBD Fusion app? I was watching it today. Percent drops to zero at idle and whenever I stand on it up to like 3500 RPM. Cruising easy at 2000-2500 rpm the commanded % is regularly 100% for extended periods, but varies with rpm it seems. It was 90+ here today. Is this "commanded" purge signal in response to some other real-world signal, or is it on some fixed algorithm? If the vacuum or valve on the canister (not really knowing what I'm talking about) weren't 100% operational, would this commanded value know or try to compensate?

 

[suprarx7nut]

Would that be the same as "commanded evaporative purge" (%) on my OBD Fusion app? I was watching it today. Percent drops to zero at idle and whenever I stand on it up to like 3500 RPM. Cruising easy at 2000-2500 rpm the commanded % is regularly 100% for extended periods, but varies with rpm it seems. It was 90+ here today. Is this "commanded" purge signal in response to some other real-world signal, or is it on some fixed algorithm? If the vacuum or valve on the canister (not really knowing what I'm talking about) weren't 100% operational, would this commanded value know or try to compensate?

I do not believe that system has any feedback loop more complex than the simple pressure sensor that ensures the system can show a sealing tank. I believe it's likely the system is underperforming for most of us that experience the fuel venting out the gas cap, but it's just a hunch for now.

 

[DTC72]

@J1000 Finally did the top mods you suggested…well most of them. I live in Las Vegas and have experienced both vapor lock or gas boil on multiple occasions including highway driving from CA to LV, on steep slow trails at altitude, after a 110+ hot summer day at Lake Mead. Over the last year or so I replaced my radiator, fuel pump, fuel filter, gas cap, and vapor canister on my 2006 LC. None of these really helped. Using ethanol free gas seemed to help some when I was in Silverton last year. This morning I put adhesive style heat shield on the exposed areas of the gas tank by the muffler and y-pipe as well as wrapped all three fuel lines from the gas tank up into the engine bay with Velcro closure heat shield. Key tip = the edges of the factory metal heat shields are VERY sharp. I now have many small cuts on my forearms! I ran out of the 10” of velcro style heat shield I bought and so I have a couple more lines to cover in the engine bay. Moving the return fuel line off the back of the engine is…I think…beyond my comfort zone. I will see how what I have done performs when I am in Silverton in a couple weeks. Thanks for your data driven suggestions!!

 

[JohnnyMackerel]

@J1000 Finally did the top mods you suggested…well most of them. I live in Las Vegas and have experienced both vapor lock or gas boil on multiple occasions including highway driving from CA to LV, on steep slow trails at altitude, after a 110+ hot summer day at Lake Mead. Over the last year or so I replaced my radiator, fuel pump, fuel filter, gas cap, and vapor canister on my 2006 LC. None of these really helped. Using ethanol free gas seemed to help some when I was in Silverton last year. This morning I put adhesive style heat shield on the exposed areas of the gas tank by the muffler and y-pipe as well as wrapped all three fuel lines from the gas tank up into the engine bay with Velcro closure heat shield. Key tip = the edges of the factory metal heat shields are VERY sharp. I now have many small cuts on my forearms! I ran out of the 10” of velcro style heat shield I bought and so I have a couple more lines to cover in the engine bay. Moving the return fuel line off the back of the engine is…I think…beyond my comfort zone. I will see how what I have done performs when I am in Silverton in a couple weeks. Thanks for your data driven suggestions!!

Since you’ve performed all the other mods with what sounds like no success I’ll be super curious to see what happens on this go around

 

[vjpkrmnc]

@J1000 Finally did the top mods you suggested…well most of them. I live in Las Vegas and have experienced both

I don't know how liquid fuel temp in the rail is meaningless. It should be the single highest temp of the fuel delivery system.
I think if it as one event, from too much temp that effects vaporization and not enough volume or thermal transfer in the tank to end the process. The gradual build up of heat over time at the fuel rail and traveling back to the tank overcomes it's ability to cool it.

After all, if your fuel pump wasn't pushing a few air bubbles the car would start. Never mind the tank venting or gas leaking out the cap or liquid itself. If any fuel comes back to the tank as a vapor, it is pressurizing the tank.
Added heat from other sources matters to. Pump itself, fuel lines close to other heat sources etc.

You're essentially going from 3.5 atmospheres absolute to 1 plus or minus, plus head pressure of the volume in the tank because your return fuel line exits at the bottom of the pump, essentially at the same level of the pick up or sock filter. Plus excess bleed from the regulator and latent pressure from the injector side all the way back to the pump check valve.

Just say for arguments sake that rail pressure leaks down to 21 psi gauge after shutdown within five minutes. (from the FSM)
Various states of tune will dictate how fast it equalizes to zero gauge at the fuel rails.
Worsening the effect with the pressure loss.

During that time temp is going up on the rails from the block. That's easy to measure.
So that combined with the pressure loss on either side of the regulator only increases the likelihood of the pump attempting to push gas bubbles resulting in a hot no start.

There are multiple compression and decompression events happening in the whole travel path. The ones we're worried about are the pressure and temp in the tank and the pressure and temp in the return line. It's just pressure, temp, and volume. One can't change without affecting the other.
All that governs how and why, after it vaporizes/boils.

The process that gets it to that point is someone else's profession. But heat is what makes it happen.

The fuel tank absolutely should be close to ambient. You can see that on a gauge on the supply to the fuel rails. I measure 25-40 degrees F difference at all times above ambient.
For example, driving around all day start and stops, gas station, bank, beer store, UPS etc all day.
Every time I get back in and see liquid rail temp it gets higher and higher at each stop, depending on how long each stop took.
At each start up a 2 or 3 degree drop happens about every 2 seconds or less until it is equal to tank temp. (assumed)
Prolonged driving at low speeds has the same effect as multiple start and stops.

For a year or more this has been a constant. 25-40 above ambient. Driving through a hail storm or a big rain where the temp drops 20 degrees outside you can see this affect the rail temp also. It drops like a rock.

If you take j1000's info also you can surmise that adding an external cooler will keep the delta between rail and tank at 20 degrees F or less.

I wish someone would install a pressure sender on the top fuel tank cover where the connectors are, and a temp sender at the bottom of the tank.

My bet is there is an equalization point and multiple crossovers with temp and pressure. The gas volume expansion is undersold in the tank, greatly. I think this should be obvious to all. I realize the tank is not a fixed container and that some gas escapes, but in this instance where the volume of the gas overcomes the containers ability to vent you might as well consider it to be inflexible.
The shear volume of the tank under pressure and clicking the cap open a few clicks lessoning the ambient pressure inside the tank even just a few PSI will cause a lot more boiling than people think. Desaturation leading to boiling. This is what is happening when liquid and gas vent out your fuel tank.

Personally I haven't had the problem for years. I put in a new pump, walbro at first and then denso stock.
I did add a heat shield, didn't measure anything but it was solved before that with the pump. For me at least.
I don't run the engine cover or the black air train.
I also don't have cats, but that only results in a 100 degree drop at the flange closest to the Y pipe.
I have a pressure sender at one rail and temp sender at the other rail.
I thought this was the most important to keep track of. I have no intention of adding other monitors.
My coolant runs at194-197 F constant. Everything related to that system is new.

As a data point, I've had the boil/vapor lock/tired fuel pump twice in two months at 7000' asl with mid 90s oat. Installed a new fuel pump last week (to replace the same PO's same denso 095-210). Now have spent a week of 110 degree air temp at stoplights followed by heavy accelerating; no boiling fuel. Monitoring coolant temps religiously now and even this week it's almost always pegged at 195.8, occasionally rising to 201 briefly. My point is, either the fuel pump helped (which I kinda doubt), or coolant temp alone is not what causes the heat that causes boil/lock/soak. While altitude is the one obvious variable in my case that probably does, my real point (as a humble LC noob having read all ~700 posts here) is I just really don't get a strong feeling that engine coolant temp is going to indicate whether my 06 is gonna shut just down on me--and start right up later after a 30 min cool down.

 

[DTC72]

As a data point, I've had the boil/vapor lock/tired fuel pump twice in two months at 7000' asl with mid 90s oat. Installed a new fuel pump last week (to replace the same PO's same denso 095-210). Now have spent a week of 110 degree air temp at stoplights followed by heavy accelerating; no boiling fuel. Monitoring coolant temps religiously now and even this week it's almost always pegged at 195.8, occasionally rising to 201 briefly. My point is, either the fuel pump helped (which I kinda doubt), or coolant temp alone is not what causes the heat that causes boil/lock/soak. While altitude is the one obvious variable in my case that probably does, my real point (as a humble LC noob having read all ~700 posts here) is I just really don't get a strong feeling that engine coolant temp is going to indicate whether my 06 is gonna shut just down on me--and start right up later after a 30 min cool down.

If you read all 700 posts you probably read that j1000 is the only one who installed a fuel temperature sensor and thus isolated the top issues/fixes with that data.