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.
Per the “he who smelt it dealt it” rule, I think it’s actually David Tracy who smells like gasoline off-throttle, not the Jeep.
The simplest answer is usually the correct one…
Per the “he who smelt it dealt it” rule, I think it’s actually David Tracy who smells like gasoline off-throttle, not the Jeep.
The simplest answer is usually the correct one…
I’m going to go with: pinhole in the diaphragm of the fuel pressure regulator. This type of failure can cause a mysterious “too rich” issue, because you have fuel escaping through the diaphragm and into the manifold reference (vacuum) line which leads directly to the intake manifold. This could explain the notable fuel smell on closed throttle, because the low manifold pressure at closed throttle would more readily draw fuel through the pinhole AND the engine would have little need for fuel on closed throttle because that mode is typically a fuel cut (injector off) situation. This failure scenario could also explain the fuel smell when parked: after parking the car the fuel would bleed down through the fuel pressure regulator’s vacuum line, into the intake manifold, through the throttle body, and out through the air filter into the open air.
Here’s how you diagnose this: disconnect the vacuum line from the fuel pressure regulator shortly after shutting the engine off. Is there liquid fuel in the vacuum line? If so, you have found your problem. You can also disconnect and plug the vacuum line, start the engine, and watch for liquid fuel exiting the vacuum port on the fuel pressure regulator. Do not set yourself on fire when testing for this!
Great idea to check!
I forgot that this can happen with fuel pressure regulators… it’s bringing back a weird memory of it happening to someone’s car like 20 years ago.
Certainly a possibility.
I’m going to go with: pinhole in the diaphragm of the fuel pressure regulator. This type of failure can cause a mysterious “too rich” issue, because you have fuel escaping through the diaphragm and into the manifold reference (vacuum) line which leads directly to the intake manifold. This could explain the notable fuel smell on closed throttle, because the low manifold pressure at closed throttle would more readily draw fuel through the pinhole AND the engine would have little need for fuel on closed throttle because that mode is typically a fuel cut (injector off) situation. This failure scenario could also explain the fuel smell when parked: after parking the car the fuel would bleed down through the fuel pressure regulator’s vacuum line, into the intake manifold, through the throttle body, and out through the air filter into the open air.
Here’s how you diagnose this: disconnect the vacuum line from the fuel pressure regulator shortly after shutting the engine off. Is there liquid fuel in the vacuum line? If so, you have found your problem. You can also disconnect and plug the vacuum line, start the engine, and watch for liquid fuel exiting the vacuum port on the fuel pressure regulator. Do not set yourself on fire when testing for this!
Great idea to check!
I forgot that this can happen with fuel pressure regulators… it’s bringing back a weird memory of it happening to someone’s car like 20 years ago.
Certainly a possibility.
Sounds like you just need to keep it floored all the time!
Sounds like you just need to keep it floored all the time!
The “only when I let off the gas” bit points me to vacuum leak. Engine vacuum is high on deceleration.
The “only when I let off the gas” bit points me to vacuum leak. Engine vacuum is high on deceleration.
I billionth the evap canister idea.
You can, in theory, blow these out and continue to use them. But, I’m sure a junkyard has a dry one already.
This is probably part of what was wrong, or led to, the fuel pump issues. I would also not rule out a clogged hard line. But, evap is first stop, IMHO. I would change the solenoid for good measure as well.
I billionth the evap canister idea.
You can, in theory, blow these out and continue to use them. But, I’m sure a junkyard has a dry one already.
This is probably part of what was wrong, or led to, the fuel pump issues. I would also not rule out a clogged hard line. But, evap is first stop, IMHO. I would change the solenoid for good measure as well.
I’d guess the evap. canister is flooded with gas or the fuel return line to the tank is worse than it looks.
Make doubly sure you are looking at a Cali. spec. schematic and not a 49 state version.
Check for diagnostic codes with a scanner.
I’d guess the evap. canister is flooded with gas or the fuel return line to the tank is worse than it looks.
Make doubly sure you are looking at a Cali. spec. schematic and not a 49 state version.
Check for diagnostic codes with a scanner.
(Me awake tonight, staring at the ceiling)
My wife (to herself): He’s probably thinking of other women
Me (to myself): I HAVE TO KNOW WHY A STRANGERS JEEP SMELLS LIKE GAS
David’s not a stranger, he’s an honorary member of all our families.
I’m honored!
Oh, sorry, I was thinking of David Lee Roth. But you’re nice too!
Intrusive Thought Of The Day
(Me awake tonight, staring at the ceiling)
My wife (to herself): He’s probably thinking of other women
Me (to myself): I HAVE TO KNOW WHY A STRANGERS JEEP SMELLS LIKE GAS
David’s not a stranger, he’s an honorary member of all our families.
I’m honored!
Oh, sorry, I was thinking of David Lee Roth. But you’re nice too!
Intrusive Thought Of The Day
It’s not that stupid 90 right before the fuel filter on the frame rail that changes sizes is it? I can’t remember if that’s a 4cyl only part or if it was on the 6’s as well.
It’s not that stupid 90 right before the fuel filter on the frame rail that changes sizes is it? I can’t remember if that’s a 4cyl only part or if it was on the 6’s as well.
I had a cracked canister in a Hyundai of mine that certainly led to a gas smell. I can’t recall it being more severe when letting off the gas though.
That canister was only accessible by dropping the fuel tank (Elantra Touring). No bueno. The purge valve is easier to replace on most cars, I would try that before replacing the canister. Outside of those EVAP related possibilities, Im not sure.
I had a cracked canister in a Hyundai of mine that certainly led to a gas smell. I can’t recall it being more severe when letting off the gas though.
That canister was only accessible by dropping the fuel tank (Elantra Touring). No bueno. The purge valve is easier to replace on most cars, I would try that before replacing the canister. Outside of those EVAP related possibilities, Im not sure.
Time to get rid of it, it’s not an EV.
…/s
Time to get rid of it, it’s not an EV.
…/s
I agree that it is most likely either the evap system or a leaking injector or bad O-ring (if they’ve been removed). I can confirm that even one leaking injector can cause a whole lot of fuel consumption and a whole lot of fuel smell. I was once not careful enough in re-inserting injectors on my SE-R (I had let the car run on gas that was too old, clogging a couple of injectors, which I replaced with spares) and this led to torn O-rings that caused massive fuel consumption and pig-rich running, at one point being so bad that one cylinder was out of operation entirely due to the plug being saturated with gas, and raw fuel was going straight through and out the exhaust, and visibly leaking out of a small crack in the header. Smell was as you’d expect.
This was my guess as well. I had an 88 xj that I replaced the fuel rail on and tore the o ring on one injector installing it. That was my symptom, fuel smell during decel.
I agree that it is most likely either the evap system or a leaking injector or bad O-ring (if they’ve been removed). I can confirm that even one leaking injector can cause a whole lot of fuel consumption and a whole lot of fuel smell. I was once not careful enough in re-inserting injectors on my SE-R (I had let the car run on gas that was too old, clogging a couple of injectors, which I replaced with spares) and this led to torn O-rings that caused massive fuel consumption and pig-rich running, at one point being so bad that one cylinder was out of operation entirely due to the plug being saturated with gas, and raw fuel was going straight through and out the exhaust, and visibly leaking out of a small crack in the header. Smell was as you’d expect.
This was my guess as well. I had an 88 xj that I replaced the fuel rail on and tore the o ring on one injector installing it. That was my symptom, fuel smell during decel.
Even though this really makes me thing this is a charcoal canister / purge valve issue, your injectors are trivially easy to get to, and you can easily do a lame check / cleaning on the cheap… I’ve tested and cleaned injectors while broken down during a lemons race by putting just enough electrical tape on the straw of carb cleaner to make a good seal against the injector hole, hooked up a 9 volt battery to the terminals, and pressed down on the spray nozzle. As this will be at lower pressure than what the fuel rail supplies it’ll make any difference in spray pattern more obvious and you may even get to see one of them go from bad to OK as the cleaner works.
Even though this really makes me thing this is a charcoal canister / purge valve issue, your injectors are trivially easy to get to, and you can easily do a lame check / cleaning on the cheap… I’ve tested and cleaned injectors while broken down during a lemons race by putting just enough electrical tape on the straw of carb cleaner to make a good seal against the injector hole, hooked up a 9 volt battery to the terminals, and pressed down on the spray nozzle. As this will be at lower pressure than what the fuel rail supplies it’ll make any difference in spray pattern more obvious and you may even get to see one of them go from bad to OK as the cleaner works.
Its the evap system, either the canister is saturated, or the valve isn’t working.