Home » My Jeep Smells Like Gas When I Let Off The Throttle And I Can’t Figure Out Why

My Jeep Smells Like Gas When I Let Off The Throttle And I Can’t Figure Out Why

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The summer is here, which means it’s top-down Jeep weather. But there’s a problem: My Jeep stinks like gas, and my neighbors are complaining, so I can no longer park it in my garage. An even bigger problem? I just changed the fuel pump, the fuel hoses, and the rubber grommets for the fuel vents. And it still smells like gas, but only in certain conditions. I can’t figure it out! So I need your help.

So, as any good online message-board-user looking for diagnostic help should do, I’ll begin by stating which vehicle I have and what problem I’m facing: It’s a 1991 Jeep Wrangler equipped with a 4.0-liter straight six bolted to an AX-15 five-speed manual transmission.

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The issue is that the vehicle smells like gas, specifically when I let off the accelerator. It seems to smell worse with the top down, and when I’m on the accelerator driving steadily, it smells fine. But as soon as I let off the throttle to coast, I can just predict it: One Mississippi, Two Mississippi, thr — and there it is. Gasoline vapors have entered my nostrils.

This is peculiar; I’ve gone back and forth a million times on what this might be, and I’m still not sure what’s going on. To provide a bit of info on what I’ve done, here’s a photo of my fuel tank, which has a new fuel pump (and gasket), new fuel hoses supply/return hoses, new fuel vents, new fuel vent grommets, and new fuel vent hoses (not shown). The filler hoses are old, but appear to be in good shape.

Screen Shot 2024 06 05 At 12.44.33 Pm

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The supply and return hoses plumb into hard lines, which seem to be in good shape:

Screen Shot 2024 06 05 At 1.17.55 Pm

There is a fuel filter in the supply line (part 22 in the diagram below), but it’s new, and in great shape.

Screen Shot 2024 06 05 At 1.27.59 Pm

The three hard lines go along the Jeep’s driver’s side frame rail, and then attach to flex hoses. One of the flex hoses (labeled 20 above) goes to a vapor canister like this:

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Screen Shot 2024 06 05 At 1.32.25 Pm

The other two ports on the vapor canister go to the air filter housing and intake manifold. Like this:

 

Screen Shot 2024 06 05 At 1.52.05 Pm

As for the other two hard lines going from the fuel tank along the driver’s side frame rail, they go into a flex line like this:
Screen Shot 2024 06 05 At 1.50.13 Pm

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Those flex lines have hard lines at their ends, and those hard lines plumb into a fuel rail. You can see the fuel rail and where the two flex lines plumb into it here in this photo:

Screen Shot 2024 06 05 At 1.47.25 Pm

And that’s it! That’s the entire fuel system. Very straightforward.

So what’s going on here? Why is it that, when I coast, the Jeep smells like gas? I have some thoughts.

One, it’s possible that when I’m on the gas, there’s lots of fuel flow going to the engine, and when I let off, that fuel then needs to be diverted back to the tank, since it’s not going into the motor. So maybe there’s an issue with the return line somewhere? I don’t see a leak, however.

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I think the Jeep is running rich, and I have a check engine light that indicates this. And I think maybe that exhaust smell becomes so bad when I’m coasting that I can smell it from the driver’s seat. But why is it running rich? And why only when I let off the accelerator?

Could I have leaky injectors? The reason why I suspect this is that, when I coast in gear, the smell is worse than if I coast in neutral. In gear, the wheels are spinning up the engine, so there should be no fuel burning. But what if fuel is being sent into the engine anyway due to bad injectors. Could raw gas just be shooting out of my tailpipe?

There’s no liquid gas coming out of my tailpipe, for the record, and the exhaust stream looks normal. What’s more, injectors don’t tend to fail in groups of three, and I’m not sure just one single leaky injector would cause the Jeep to smell this bad.

Could my vapor canister be… full? Honestly, I’m not sure what’s going on. All I know is, the Jeep smells like gas when I let off the skinny pedal, and it’s precluding me from daily driving this thing in beautiful California, so I need to figure this out! Any help would be greatly appreciated.

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Zwill
Zwill
14 days ago

Ruptured diaphragm in the fuel pressure regulator?

Nathan
Nathan
14 days ago

My guess is it is actually the valve on the vapor canister. The valve is supposed to shut off at low RPM and open at high RPM when the engine can actually burn off the vapor.

I am biased because I had to change this on an old Mazda 3. It was like a $15 part for a new canister assembly that includes the valve. The biggest problems were right after filling up the tank. It was too rich to start and one time it even misfired, but would eventually fire up. Replaced the part and all problems went away.

Joke #119!
Joke #119!
14 days ago

Also, gasoline can evaporate pretty quickly, so seeing a leak might not be so easy.

Probably need someone under the car while you press the pedal and let up.
If someone has to be under there while you’re coasting in gear, um…

Joke #119!
Joke #119!
14 days ago

Probably need to pinpoint the location of the odor. If it is inside the engine compartment, then yes, definitely do not drive it.

Naterator
Naterator
14 days ago

I’d suggest checking or replacing that vapor canister if you can’t find any leaks. Could also be running rich from an injector problem, but you’d think that would throw a code.

This also sounds crazy, but have you checked the gas cap? I had vapor fumes swirl around my car when my gas cap gasket went bad.

Last edited 14 days ago by Naterator
Farty McSprinkles
Farty McSprinkles
14 days ago

I echo the people saying check the fuel injectors. I bet one or more is done. If they are not working properly they can let fuel continuously flow. The smell when coasting and sitting (no spark) makes this even more likely.

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