Gasoline Odor

[EddieC]

'08 Tahoe has an illusive gasoline odor seeming to be near the driver's rear wheel well after sitting a short time after driving.
No obvious leaks are seen under there nor on the driveway.
In the morning after sitting (outdoors) there is no noticeable odor but a short drive and stopping makes it prominent.
I don't currently have a CEL on. A year ago there was a P0449 code and new vapor canister vent valve/solenoid assembly and gas cap were installed, reset the code and the CEL stayed off.
Our shop owner said he would do a smoke test on the system to try to see what happens relative to leaks.
Is there venting in the system that would emit a strong odor in the left/rear area?
Any other ideas?

 

[Fless]

Driver's side (left) or passenger side (right). You indicated both.

There shouldn't be any venting of fuel vapors; that's what the emissions system is supposed to control. My '04 had the fuel smell (left rear) when it had a defective fuel pump gasket, as well as it wouldn't pass the SUV's emissions test (MIL).

 

[rdezs]

The canister vent valve has a fresh air intake tube, that is usually attached up into the body work, wire tied to your fuel filler hose right below the area of the gas cap.

I'm wondering if you might be getting excess pressure in the fuel tank due to a malfunctioning purge valve. (Pretty common failure item. You'll see it on your intake manifold, opens when the engines running to suck the vapors and burn them. Closes when you turn the engine off to avoid flooding the engine with vapors. Usually they stick open and create starting issues, although they can just as easily stick closed.

As mentioned in the previous post, you really need to take a look at the top of your fuel pump. They're known to rust all the way through. It can be tough to get your eyes on it..... This is where one of those fiber optic devices with a small screen come in really useful. Pretty affordable on Amazon. Think I've had mine for 5 years.

Teslong Endoscope Borescope https://a.co/d/bXw8B2B

 

[EddieC]

Driver's side (left) or passenger side (right). You indicated both.

There shouldn't be any venting of fuel vapors; that's what the emissions system is supposed to control. My '04 had the fuel smell (left rear) when it had a defective fuel pump gasket, as well as it wouldn't pass the SUV's emissions test (MIL).

Left side is correct. Right was Typo.

I understand there should be no venting but could there be? If the canister vent valve/solenoid malfunctions?

I had the wheel and fender liner off a while ago to look in there and the tank well was dry. Is that the area you are referring to?
Another clue might be that there is no odor after it sits, like in the morning, so something occurs when driving to cause a change and allow the odor.

 

[rdezs]

If the purge valve isn't working and pressures building up in the tank, from heat for example.... It could definitely flow backwards through the vent valve to the fresh air intake.... Which could suggest that fairly new vent valve is stuck open also.

 

[EddieC]

Left of course. Typo.

The canister vent valve has a fresh air intake tube, that is usually attached up into the body work, wire tied to your fuel filler hose right below the area of the gas cap.

I'm wondering if you might be getting excess pressure in the fuel tank due to a malfunctioning purge valve. (Pretty common failure item. You'll see it on your intake manifold, opens when the engines running to suck the vapors and burn them. Closes when you turn the engine off to avoid flooding the engine with vapors. Usually they stick open and create starting issues, although they can just as easily stick closed.

As mentioned in the previous post, you really need to take a look at the top of your fuel pump. They're known to rust all the way through. It can be tough to get your eyes on it..... This is where one of those fiber optic devices with a small screen come in really useful. Pretty affordable on Amazon. Think I've had mine for 5 years.

Teslong Endoscope Borescope https://a.co/d/bXw8B2B

I changed the purge valve on the left valve cover area last year too but that is not to say it's working.
What would be a test for that, if any?

 

[EddieC]

Going to crawl back under again tomorrow to see is something looks amiss. Wires, hoses, etc.

 

[rdezs]

With the engine off you should not be able to blow through it. They usually fail with the valve inside open. To properly test it, you need a Tech 2 or bidirectional scanner that's capable to send commands.

I have ran across them before in a failed state with no check engine light or code

 

[rdezs]

If you didn't use genuine GM or ACDelco.... The aftermarket ones typically don't last that long

 

[solli5pack]

I changed the purge valve on the left valve cover area last year too but that is not to say it's working.
What would be a test for that, if any?

Seal and purge test will tell you everything you need to know....

 

[Fless]

The purge valve on the engine should be closed when no voltage is applied (as in ignition off). No vapors should be able to move through it.

The canister vent valve should be open when no voltage is applied (as in ignition off). It should not vent any fuel vapors, as it's an intake vent.

If you're interested Mike at Go Tech (Wells) does a great job of explaining evap systems and tests. Some are specific to GM systems.

GoTech

Automotive repair content hosted by ASE Master Certified technicians with a focus on diagnosing and repairing today's problem vehicles with speed and accuracy.

www.youtube.com

 

[tom3]

Where do you live? Up here in the rust belt an 08 might have some rusted lines and a rusted vapor line from the tank will let fumes out without actually seeing a gas leak. Take a close look at those lines especially at support brackets.

 

[EddieC]

If you didn't use genuine GM or ACDelco.... The aftermarket ones typically don't last that long

All oem GM.

 

[EddieC]

The purge valve on the engine should be closed when no voltage is applied (as in ignition off). No vapors should be able to move through it.

The canister vent valve should be open when no voltage is applied (as in ignition off). It should not vent any fuel vapors, as it's an intake vent.

If you're interested Mike at Go Tech (Wells) does a great job of explaining evap systems and tests. Some are specific to GM systems.

GoTech

Automotive repair content hosted by ASE Master Certified technicians with a focus on diagnosing and repairing today's problem vehicles with speed and accuracy.

www.youtube.com

Would you expect a CEL or code if either is not functioning properly?

 

[EddieC]

Where do you live? Up here in the rust belt an 08 might have some rusted lines and a rusted vapor line from the tank will let fumes out without actually seeing a gas leak. Take a close look at those lines especially at support brackets.

Good point.
I hoping the mechanic's planned smoke test might help in that regard. He said they introduces smoke in the system through an inlet under the hood throughout the system including the tank.

 

[rdezs]

Would you expect a CEL or code if either is not functioning properly?

Usually there's no code for some reason....

 

[89Suburban]

'08 Tahoe has an illusive gasoline odor seeming to be near the driver's rear wheel well after sitting a short time after driving.
No obvious leaks are seen under there nor on the driveway.
In the morning after sitting (outdoors) there is no noticeable odor but a short drive and stopping makes it prominent.
I don't currently have a CEL on. A year ago there was a P0449 code and new vapor canister vent valve/solenoid assembly and gas cap were installed, reset the code and the CEL stayed off.
Our shop owner said he would do a smoke test on the system to try to see what happens relative to leaks.
Is there venting in the system that would emit a strong odor in the left/rear area?
Any other ideas?

The fuel pump sits in a recessed area in the top of the tank. I can be very likely the pump or it's lines have corroded enough to develop some pinhole leaks that would puddle in the recessed area but not enough to run down the sides of that tank. You can try to reach your hand in up there to feel if it is wet. I had a bad fuel odor for over a year before I figured it out. There was no sign of a fuel leak from under the vehicle.

 

[rdezs]

That's another good example of something that should have triggered a CEL if it failed to self test every time you start it. Our 2014 Escalade last week did not set a CEL... Instead popped up on the dash to tighten the gas cap. (Had to replace it, wouldn't click when you tightened it) No idea how the ECM determined that was the problem and not a leak somewhere else.

 

[Fless]

Would you expect a CEL or code if either is not functioning properly?

I wouldn't necessarily expect one to show up, at least not immediately.

 

[Fless]

That's another good example of something that should have triggered a CEL if it failed to self test every time you start it. Our 2014 Escalade last week did not set a CEL... Instead popped up on the dash to tighten the gas cap. (Had to replace it, wouldn't click when you tightened it) No idea how the ECM determined that was the problem and not a leak somewhere else.

The emissions drive cycle requires many conditions to be met, so it's not done every time the engine is started. It will only test on a cold start, for example, with the ECT and the ambient temps being within 'x' degrees. There are other conditions for it to perform the test.

Your dash message was likely the first occurrence of the emission test failure -- a pending code. The next time it failed (within a certain number of key cycles), the MIL would light up.