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.
Just use an open flame around the engine to look for leaks, then show us your new hairstyle
First thought was vapor canister.
Second was replacing the o-rings on the injectors. Cheap job.
My parsh was starting to get a little gas-stinky before the injectors gave up the ghost. When they finally stopped squirting entirely, it was VERY stinky in there. So, check them injectors. Make sure they’re all actually firing.
Does it not always start on the first key turn after you park when you return from a quick stop at say a c store? My moneys on leaky injectors?
Is it shooting gas onto your feet again?
Odd-ball suggestion – check the seal around your throttle body. If you’re already running rich (per the CEL) you have an abundance of fuel in the intake and you take your foot off the gas pedal the motor is no longer “sucking” the air hose to the throttle body(or throttle body to the intake) and if it’s really running rich then that lack of pressure may be enough to allow the fumes to escape through a not tight seal?
If gas fumes escape the pull of a carburetor then I don’t see why they wouldn’t also escape a throttle body.
Discounting an actual fuel leak of some kind, my first thought was the vapor trap and lines. A couple things to consider might be the fuel cap itself. Is it original? The venting mechanism may be faulty. Also, like you said, the canister itself. Maybe swap it out with another junk yard unit just to see if the smell goes away.
It’s definitely more difficult to diagnose, assuming it’s part of the vapor emissions, since the vehicle is pre-OBDII and doesn’t have built-in monitoring. Taking that into consideration, I’ll bet your resources at Galpin have a smoke tester you could run on it to identify even the smallest of leaks.
You either ate too many chimichangas, or something is terribly wrong…
IIRC, Some 4.0s were known to have sticky/leaky injectors. Also, it’s very common for old fuel pressure regulators to rupture the diapraghm. High vacuum situations will pull raw fuel right into the manifold through the regulator if the diaphragm has pinholes.
…and now, a rebuttal from the non-mechanically inclined, Minimalist division, representative, me.
Sell it. Now. Along with everything else except your 2021 i3 and your Mustang. Always keep the Mustang.
Your SO will thank me.
Why would he sell a Jeep that has one thing wrong with it, that he enjoys driving, that can be driven places his i3 and Mustang can’t go? He just wrote about how enjoyable top-down off-roading was days ago, selling this Jeep would be one of the most illogical things he could do.
Replacing it with an old Toyota FJ40 would be smarter.
Telling DT to sell a Jeep for any other off-roader feels sacrilegious.
He just sold a golden eagle and was ogling xterras, so…
Sawzall one of the i3’s. Then there is a reason to keep both.
His SO is apparently on board with the car hoarding he’s currently got going on so far.
Get the CEL code first. It will tell you a lot. It’s an easy process, and somewhere out in the forums is a list of codes and meanings.
1. Turn the Jeep off.
2. Turn key to accessory and back to off five times within 5 seconds, not turning the Jeep on at all.
3. CEL will being to flash, count the flashes. I believe a pause in flashes separates the “numbers” of the code.
Code list here: https://www.wranglerboard.com/threads/obdi-yj-trouble-code-reference.262/
I thought about this too, but I made the assumption that it wasn’t monitored in OBDI. I may be wrong, but it’s obviously an easy check.
When I put my YJ back together the engine threw 2 codes. I went through them one by one and it ran like a top after that.
Such an easy check, I would start there.
I vaguely remember getting morse code CEL diagnostics on my old ’89 Montero but I was going through the glove box with an electrometer. I think? I may have dreamed that whole ordeal.
And you’re sure it’s not exhaust being pulled back into the passenger compartment? When I had my YJ I always kept the back window zipped in place to because of this very reason.
Neighbors say it smells like gas just sitting.
IIRC, the owners manual even says that if the back window is not zipped in place, you better have the door windows down, too, or you’re gonna have a bad time™.
I know you said you checked the fuel filling bits but I would seriously consider pulling all the bits out and fully inspecting. I had a fuel smell with my Grand Marquis which I know are prone to rotten fuel filler necks. So gas smell + CEL = fuel filler neck. I poked and prodded and could find nothing. I replaced purge valve and other bits and issue remained. Finally pulled the whole neck and there it was the rubber grommet where the neck meets the fuel cap was entirely corroded and falling apart but it was hidden by the mounting points inside the fuel door. Replaced neck and fuel cap and good to go!
Have you checked the carb?
It’s fuel injected!
But have you checked the carb? It’s always the carb.
It doesn’t have one!
So you haven’t checked? I think I’ve made my point.
It could also be the supercharger. Have you checked that?
It’s probably lupus.
It’s never lupus.
It was lupus, once!
and the look on his face was priceless.
Why not just get some fuel detector dye and see where it is leaking
When you release the throttle also remove your fuel shark from your cigarette lighter. What people don’t know is that fuel sharks can generate gas instead of just saving a bit. If you are cruising at a certain speed and the fuel shark is working optimal the flow is so steady that it can’t react that quickly to throttle changes, so when you release the throttle completely you are overfilling your gas tank.
Same in the garage, when standing still it will slowly fill up the tank, always unplug your fuel shark when standing still. This is something big fuel shark doesn’t want you to know, but if you do your research yourself you will find the answers.
There’s a lot more they don’t tell you. For example big fuel shark is in cahoots with big blinker fluid, if you use a fuel shark you don’t need to refill your blinker fluid! But they don’t want you to know that, they want you you to keep buying that sweet sweet blinker fluid! I haven’t refilled mine since I used my fuel shark.
My Renault 4 also started smelling like gas the very first day of summer heat we had around these parts, but it was an easy dagnostic: the nut connecting fuel hose to the carb got loose and fuel started dripping right on top of the exhaust manifold. Not ideal, especially in hot weather. And because the airbox nuts aren’t unscrewing, I haven’t been able to really get down there and tighten the loose nut that’s been causing this.
Only thing I can do is tighten it a bit manually whenever it gets loose and fuel leaks out – which is immediately noticeable because of the intense smell of gasoline. However, tightening the nut manually to stop the leak means it’s easy for engine vibrations alone to cause it to quickly become loose again, so in the last month or so I’ve had to deal with this three times already. Anyone has any tips for how to remove nuts that won’t unscrew? I’d really love to be able to remove that air box to have proper access to the carb.
Hold up! You have a Renault 4?! I freaking love those! I very briefly considered importing one to the states, but after the debacle that has been my Peugeot import, my wife promptly shot that idea down with extreme prejudice. I must know more! What year? How long have you had it? How is it?
Yup, it’s my daily driver, and currently my only functional car 🙂 They are still around in decent numbers here in Portugal and it’s probably the biggest single-car community in the country. Pretty much every other boomer and old gen-xer had one at some point. I grew up in one, as did my wife; we had one as our wedding car, which belongs to her godfather and is also daily driven.
A few years ago we found ourselves informally guarding our late neighbour’s 1991 GTL (it’s a long, somewhat sad story), which we maintained and drove for almost a year before finally purchasing it from her estate. It’s been the best car ownership experience I’ve ever had. It’s a reliable little car that’s cheap to maintain, and while things do break here and there, everything’s an easy and cheap fix. And it’s dependable too, only left me stranded once in five years, when the clutch gave in a couple of years ago. I learned to wrench on it and would normally do my own carb work, but I have no idea how I’m going to extract the airbox nuts to access the nuts and screws that have been getting loose. But it also needs some steering work that will be done by my mechanic, so this will likely get solved then – once the Volvo V50 I purchased recently has had its engine transplant completed.
That’s awesome! I love those things more than I should, but admittedly I have never actually seen one in person. Gotta love that the 30+ year old car is the most reliable of the lot.
These Cléon-Fonte engines are actually very reliable, especially the C1E version fitted to late Renault 4 GTL models, which got detuned from 44HP to 34HP in the mid-80s, so they almost always run understressed. It does leak oil, which is only normal in a 30 year old car, but as long as the carb and distributor are properly tuned, it runs great. I plan on swapping out the distributor for an electronic ignition system the next time points fail – and they will fail, that is something of an Achiles’ heel for these cars. It should improve fuel efficiency and spark plug life too, and for about 1.5x the cost of getting distributor points fixed, it’s a no-brainer really.
That’s awesome. I want one! Yeah I don’t remember the last time I had a car that didn’t leak some sort of fluid. My wife’s are generally mostly leak free, but mine are always needing something. That’s what happens when I pretty much exclusively drive 90s cars.
My guess is that your evap purge valve (or a related component) is hosed. When you’re hitting the gas, the vacuum sucks the fumes into the intake; when you let off, the fumes in the canister escape into the atmosphere. The problem is worse with warmer weather, and naturally more noticeable with the top off.
FWIW, I’ve been having a similar problem with my Del Sol but have been too cheap/lazy to start throwing parts at it.
I suggest this. I’ll email it to you as well.
I would check the fuel pressure regulator, the only thing to make a fuel injected 4.0 to run rich.
I had some issues with leaky fuel injectors on my ‘90 MJ and a nice set of remans with new seals sorted it out no problem. You forgot to give us the exact CEL code you are getting though, as any good online message board user looking for diagnostic help should know 😉
Coasting in gear pulls a lot lower intake manifold vacuum than idling in neutral or other driving, as low as 20 kPa or less while idle is typically 40 or so. I’d start checking anywhere vacuum lines and fuel system meet and a leak would allow fuel into the manifold without an external leak. The fuel pressure regulator suggestion and diagnosis by widgetsltd is a good suggestion, as is the vapor canister.
I don’t know the specifics of your jeep’s EVAP emissions, but some vehicles had a solenoid valve or even a vacuum valve that would only connect the vapor canister to the intake at idle or close to WOT, so that the higher pressure doesn’t draw to much fuel vapor from the tank in to the engine and significantly affect the AFR when air flow is lowest and vacuum is highest. This might be a separate valve or integrated into the canister, but id check it and the vacuum lines running to it for leaks since that could cause it to not close, allowing the engine to draw down the tank pressure excessively and result in rich running when coasting
Did the issue exist prior to changing the fuel tank and performing the related service?
It did.Though it seems I did improve the issue, though I’m not sure that even makes sense.
I always see a new problem as an excuse to buy another tool…
In this case I wonder if a hydrocarbon or combustable gas sniffer might help you narrow down where it’s coming from. Looks like Amazon carries a few options, or alternately Galpin might have a tailpipe (or wherever you stick it) emissions sniffer for CA smog checks.
It is unlikely that the Carbon Canister is saturated. You’ve got the most primitive style the constant flow. The purge port is connected directly to the intake and the amount of flow is controlled by an orifice. That means the purge will be highest when you are off the throttle and unless something is pumping liquid fuel into it it won’t provide enough fuel for you to smell it in the exhaust, though it would dump it out the bottom of the carbon canister which is open.
Start with the CEL and see what it says. Then pull and read all the plugs to see if they are all running rich or only some of them.