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

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.

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.

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

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

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:

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

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:

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:

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.

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.