[Adventurer55]

2007 Jeep Commander, 4.7. There is a fuel smell coming from under the hood when it's running and for a bit after it's shut off. It goes away after a few minutes. I've had my tech look at it several times. No fuel leaks at all. He said he believes that it's the vapor purge system. I have no clue how this is supposed to work. Anybody got any suggestions. Backstory, the engine has been changed, but this problem was present prior to replacement. Thanks

 

[Tony K]

IDK, but after last Friday, I'm wary of any kind of fuel leak, even on a diesel. We had a fire in the engine compartment of a Peterbilt, caused by a stuck starter, which sits very close to the fuel pump on a 3176 Cat. No major damage, and the local mechanic got it back running shortly. I'm just glad it was wet in the field, because it could have been a really bad situation had it been sitting in corn stubble. I had fire on the firewall and under the truck. A 3 lb ABC is all that kept that from turning into a Peterbilt Flambee and some sort of corn casserole (it wasn't popcorn). The 8 days from Friday, Nov 13, to last Friday was an almost unending series of bad luck, yet we still got the harvest in finally on Monday.

 

[AllanC]

. . . No fuel leaks at all. He said he believes that it's the vapor purge system. I have no clue how this is supposed to work. Anybody got any suggestions. . . . .

I would tend to believe that there is a major leak in the vapor recovery system. Do you have any diagnostic trouble codes stored in the PCM (powertrain control module) that would indicate evaporative emission system leak?

There is a vapor purge valve in the engine compartment. When the engine is running and certain conditions are met, the PCM will energize the purge valve briefly to draw a vacuum on the evaporative emission system to include the fuel tank and fuel filler tube. This is a test on the integrity of the evaporative emission system. There is a tube that connects the vapor system at the top of the fuel tank to the purge valve in the engine compartment. If there is a crack in that hose you will get gasoline vapors escaping during engine operation and for a short time period after engine shut down.

Attached image shows a picture of the valve. Find it and check the hoses to the valve.

 

[Adventurer55]

I would tend to believe that there is a major leak in the vapor recovery system. Do you have any diagnostic trouble codes stored in the PCM (powertrain control module) that would indicate evaporative emission system leak?

There is a vapor purge valve in the engine compartment. When the engine is running and certain conditions are met, the PCM will energize the purge valve briefly to draw a vacuum on the evaporative emission system to include the fuel tank and fuel filler tube. This is a test on the integrity of the evaporative emission system. There is a tube that connects the vapor system at the top of the fuel tank to the purge valve in the engine compartment. If there is a crack in that hose you will get gasoline vapors escaping during engine operation and for a short time period after engine shut down.

Attached image shows a picture of the valve. Find it and check the hoses to the valve.

View attachment 72886

Thanks. I'm familiar with the location of the valve, but wasn't aware of how it works. I've had suspicions that there was a breach somewhere. Now I know how to proceed. Any chance the valve itself could be the culprit?

 

[AllanC]

. . . Any chance the valve itself could be the culprit . . .

Most likely failure of the valve is that it fails to open, sticks and stays open even when not energized or is partially open when not energized. In those situations the vapors from the tank would migrate through the vapor hose and into the intake manifold. With the engine running these vapors are ingested into the engine and you would not smell them.

If the engine was not running the vapors would have to migrate backwards through the throttle body, into the air cleaner box and filter and out the fresh air intake in the grille or engine compartment. I doubt that would happen.

If the purge valve fails to function properly there would be a series of evaporative emission diagnostic codes set. Do you have any diagnostic codes set in the PCM?

 

[ImperialCrown]

Any breach on the canister side should set an evaporative leak code. If the breach is between the valve and the intake manifold, it won't set a code.
I have had oil-soaked rubber hoses and fittings swell and no longer seal at the ends.

The crankcase breather/PCV fumes can also be mistaken for fuel odors. The 2 breathers for the left and right bank hoses must be attached at the rear of the engine. Make sure that the PCV is drawing vacuum well. The inside of the air cleaner at the breather intake should be dry.
Oil leaks onto a hot exhaust can also cause hydrocarbon odors.

You should have a hose diagram label under the hood to show hose routing?

 

[Adventurer55]

Most likely failure of the valve is that it fails to open, sticks and stays open even when not energized or is partially open when not energized. In those situations the vapors from the tank would migrate through the vapor hose and into the intake manifold. With the engine running these vapors are ingested into the engine and you would not smell them.

If the engine was not running the vapors would have to migrate backwards through the throttle body, into the air cleaner box and filter and out the fresh air intake in the grille or engine compartment. I doubt that would happen.

If the purge valve fails to function properly there would be a series of evaporative emission diagnostic codes set. Do you have any diagnostic codes set in the PCM?

No, it hasn't set off any codes. The next time I take it in for service I'll have them look for a bad line. The wife, who drives it to work is off for a bit as she has covid-19. I want to thank all of you for the help and have a good Thanksgiving.