Hi all,

The other night I woke up to the smell of fuel in my house and tracked it back to my car.

The car is a 1991 Z28 5.0L. I'm the original owner, and have been daily driving it for the last 2 years without any issue.

I checked for any obvious leaks:

• No fuel spots on the floor in the engine area or under the length of the car
• No moisture/fuel around the injectors or along the fuel rail
• Fuel line connection points to the lines of the fuel rail in the engine bay are dry
• Gas gap is tight (original non-vented cap)

Tank appears to be holding pressure. From most of the posts I look at, this is normal. When I remove cap I get hissing as air is sucked into the tank (negative pressure in the tank). The only issue I've noticed is that it can be enough negative pressure that it appears to be sucking in the walls of the tank as I hear the tank "expand" when I release pressure by removing the cap (when filling, etc.)

I don't have any fuel delivery issues, car runs fine.

I don't have a lift or any easy way to get under the car, so any help is appreciated to help diagnose what's going on!

 

Sounds like a leaky fuel pressure regulator.

That happened to mine a few months back.

 

Would that be leaking from the regulator itself under the intake manifold or would it be causing pressure to cause a vapor or other leak somewhere else?

I'm not experiencing any symptoms of a bad regulator (engine runs fine, no black smoke, no CEL, etc.).

I have been trying to isolate the smell to the engine bay or back by the tank... its fairly strong so its been harder to identify the location.

 

Another candidate might be the EVAP canister. Make sure the purge system is clearing out the canister once the system is up to temperature and at light to moderate cruise operation.

 

So in essence (excuse the pun, French speakers) you're telling us it's leaking from "the car", and you're expecting the Internet to be able to track it down remotely for you.

Right.

Anything rubber is of course immediately suspect. Regulator, lines (both at the engine and at the top of the tank), O-rings, injectors, etc. The vapor canister is another potential problem: the charcoal gets saturated with gas, and reeks. The steel fuel lines could be rusted through. The tank might even have a pinhole rusted through it; happens quite often, especially in cars that sit outdoors unused for long periods, from condensation droplets inside the tank rusting it through from the inside, even though it looks perfect on the outside.

I suggest driving the car for awhile and letting it sit outdoors on a sunny day with no wind, so you can track down at least the general area where the smell is strongest. Then once you know that, you'll at least have some idea of where not to waste your time looking for it.

 

If the smell is so strong that the whole garage smells the same, then roll the car outside where the cloud of odor will dissipate into the universe and then you can actually follow your nose to where the smell comes from.

None of us have fancy dancy lifts. We have a floor jack and jack stands and get down on the floor. That's part of owning an old car.

 

I love sarcasm on the internet! Not for nothin, but I did do and say in my post a few things I did do before posting, including items I checked and verified as not leaking (injectors, lines, etc.).

Thank you both Sofakingdom and QwkTrip... This list of things did help me start to isolate and rule things out

• Verified again that under the hood, the engine bay looks "clear" and no leaks present and any of the expected places.
• All of the rubber lines to the EVAP canister look good and are not dry/brittle.
• Leaving the garage door open (I didn't roll it outside as its windy where I am today), I did isolate the smell to the rear of the car. This makes sense to me as I do not smell it in the cabin of the car when driving (something I'm sure would smell inside the car if it was leaking in the engine bay).
• I remembered that the night it started to smell, I had filled the tank that afternoon. I did not overfill or add more gas after the pump shut off

Unless there's something from the EVAP system that could be causing the smell to come out from the back, would it now be most likely that there's either a hole in the tank/filler neck or possibly in the lines to the tank?

What makes this all the more weird is that the car runs perfect. If I had a rusted out fuel line (pressured), I would expect to not run right. If I had a hole in the tank, I would expect it wouldn't hold pressure like it is (hisses/are rushes in when the cap is opened). Would that point towards one of the evap lines and/or valves being plugged up and forcing some venting out by the rear/tank?

 

Filler neck solder joint cracking is a familiar thing in these cars.

 

I did see that recall as well as it being mentioned in other related threads. It seems to fit... but wouldn't that prevent the negative vacuum from forming in the tank?

 

Kinda depends on how big of a crack it is.

 

Did you check the valve that is connected to the EVAP. Its round, about the size of a half dollar and maybe 1/3" tall. Has an in/out on it. I found mine sticking, had some gunk in it, probably from sitting in storage for so long. You can take it apart and clean it up, or they are still available for sale. Also make sure your EVAP solenoid still working if that wasn't already mentioned.

If you find any of that to be an problem, there is this: https://www.thirdgen.org/forums/tech...ter-purge.html

 

Thanks LiquidBlue. If you're talking about the Canister Purge Valve (GM Part# 17087240; https://a.co/d/aqMTfcm), I did pull it and check. Air will flow through it from Tank side to Can side when I pull a vacuum on the 'vac' side. I can get air to pass through with a little extra force even when I don't pull a vacuum on the 'vac' side. So, its seems to be working... but I guess replacing it wouldn't hurt just to verify that its not "weak".

I did try and push air in the opposite direction (canister to tank side) and it didn't flow... so it seems the valve is working to prevent fumes from going back to the tank from the canister (1-way valve).

With the control valve back in place, I thought I could feel some vacuum from the tank side of the valve. I may have to go back out and check again, this time at the canister.

Note, the leaking fuel smell isn't while the car is in operation. It seems to only been when its parked.

Thanks for that link, I hadn't seen that yet. With the parts verified as working as you suggested... it'll be good to have in case it ever does go on me.

 

Nevermind... I went back out and pulled the line(s) from the solenoid on top of the tank directly. When I pulled the vacuum line from the engine... definitely getting solid vacuum on that side of the solenoid. The side pulling from the control valve/tank had no vacuum when I plugged the vacuum line back on the top of the solenoid. These solenoids fail open correct? If so, then it's working as expected.

 

I forget, but you can take 5V or 12 V and apply power and ground to the solenoid and hear it open/close if you want to test it.

 

Hey All...

Thanks again for everyone's help. I had the car in for annual inspection and asked them to see if they could find the source of the leak, and they did!

Turns out I must have a pinhole leak of some sort, they said it was coming out from behind the tank straps.

I guess its time to replace the tank. Car only has 66k miles on it, but rust is a killer no matter the miles.

Are there any good threads on what tank to replace it with? I'm not up to that job on my own, but want to make sure we get the right parts in place.

I'm assuming I should do the pump/lines while they have it out?

 

There is little doubt that the in-tank pump unit should probably be replaced at the same time, and the lines should be inspected when the tank is removed.

The source for the specific replacement is up to you, but I would avoid any that are painted or powder-coated, and move to a plated version. Just like POR, I've seen far too many powder-coated and epoxy coated pieces go away very quickly due to the coating holding in more moisture than it keeps out.

 

If it were mine, I'd look into having your tank repaired. its seems like aftermarket tanks are hit and miss. There are many posts around this forum covering the subject. just google "thirdgen.org gas/fuel tank" and just read all the posts to get educated. There are those who have had success with aftermarket, and then the next guy will say I tried same one and it didn't work so well. A ton of varying opinions and experiences out there. If you still decide to go aftermarket, and live in the TX area, I could be a potential buyer of your factory tank - been looking for one.