Fuel smell in cabin ONLY when tank is full

[rjd2]

Hi folks-so I have had DMC #2 on the road for a good chunk of 2023 after a fairly big recommissioning/restoration, and for the most part, all is well. Still some things I'm shaking out, but I have one that really got to me today:

As a backdrop to the issue, here's what has been done to this car: cleaned fuel tank, replaced fuel pump/accumulator/all fuel hoses/fuel filter/all evap hoses at the front trunk area, as well as new filler neck. To my knowledge, EVERY flexible hose in the vehicle has been replaced. The car then went to Dave Bauerle to have all my work checked over. Came back running well.To date, I have been filling the car to the 1/2 way or 2/3 point in the tank, and have never smelled fuel. In prep for winter, I will sometimes go fill up the tank on a car, add the appropriate amount of sta-bil, and then consider it ready for the first freeze. I did this, which was the first time this car has had a full tank of gas. I got some fuel fumes after the fillup, but it was only 2 minutes to get home. The car sat for 4-5 days. I get in today to drive, no smell. As soon as I take off, the cabin started to smell of evaporating fuel. I did 2x 15 minute drives, and not ALL the time, but probably 1/2 the time, I smelled fuel. I stuck my head in the front trunk and engine bay, and couldnt smell it at all. I checked for leaks, and nothing. Any ideas on the cause of this, or is this normal? My other DMC does not do this. I don't know if it's related, but I am also still having the experience in which starting the car almost anytime takes 20-30 seconds of cranking. Once it starts, it runs fine(it hunted for an idle today for longer than expected but not a big deal).

Thanks for any tips on the fuel odor issue.

[WHO1DMC]

I would make sure everything at fuel pump is tight well sealed. If you whent with the fuel pump upgrade with integrated sender the sender delete sometimes can leak.
This is going on only smelling fuel from a full tank.





Dave B.

[rjd2]

I would make sure everything at fuel pump is tight well sealed. If you whent with the fuel pump upgrade with integrated sender the sender delete sometimes can leak.
This is going on only smelling fuel from a full tank.





Dave B.

Gotcha. Thanks. Yes, it's an integrated "GM style" unit from Delorean Industries, IIRC. maybe i should pull the internal shroud piece at the frunk and check the tank area.

[FLUX @88]

mine will do this from time to time when i fill up (same set up as you), the close out cap (where old fuel level sensor went) will pop off and it will seep there. My experience. I will then twist the cap back on... I have also tried another cap with same results.

[Helirich]

It?s your fuel cap. Mine looked fine and went on tight, but had the fuel smell when full. It was worse if I did sharp turns or fast stop. Checked everything and was pulling my hair out. Cut a rubber gasket out of some old inner tube. Put it under the cap and gone. I ment to get another cap, but it?s still there. No smell.

[JBaker4981]

If you are running an all in one Fuel Pump/Sender, ensure that the cap is on tight on the unused Fuel Sender opening. This spot is notorious for leaks and fuel smells

[David T]

It?s your fuel cap. Mine looked fine and went on tight, but had the fuel smell when full. It was worse if I did sharp turns or fast stop. Checked everything and was pulling my hair out. Cut a rubber gasket out of some old inner tube. Put it under the cap and gone. I ment to get another cap, but it?s still there. No smell.

Pull the cover to the fuel tank where the spare goes and also the one under the fuel cap. Go for a ride and do some fast stops. Get out and see if there is any wetness anywhere that would indicate leakage when you have a full tank. A leaky fuel cap is likely. Also check the fuel neck. If you put the nozzle in and lean on it you can bend the neck and the gas cap will not seal properly.

[Jonathan]

+1 to what Dave T. said about going for a drive and slamming on the brakes a couple times. You will see where the fuel is coming from. And the reason you smell it more when driving is because the cooling fans (or to a lessor extent, just the air passing under or through the car) will push those fumes towards the cabin air intake.

[Michael]

I had the exact problem. My fuel sending unit retaining ring was leaking. It smells when the tank is full because there is much more pressure (weight) forcing the fuel out when you brake. I don't know if you have the new sending delete pump or the OE sending unit but you can see if it is leaking by looking behind the left front tire after a drive. I put a new seal on mine but it didn't fit right so I got the old seal and used fuel proof gasket sealant. Hasn't leaked in years since.

[Bitsyncmaster]

My car had the TankZilla sender and a notch was cut in the lip of the tank. Not sure if the notch is normal for the stock tank. But anyway I had no luck with new blocking cap so I ended up machining a plate to fit in the original lock ring.

I tested for leaks by filling the tank right to the top of the fill cap. No leaks even overnight with that overfill.

[rjd2]

just wanted to follow up and say that it was in fact the cap for the sending unit hole; because of the orientation of the hoses in the new GM style fuel pump, it's hard to get access to the cap(the most ergonomic installation has them lying directly over the cap). I didnt have it fully secured. tightened it down, checked it and its "fuel tight". that tip of slamming on the brakes and then getting out was gold! thanks ya'll!

[JBaker4981]

just wanted to follow up and say that it was in fact the cap for the sending unit hole; because of the orientation of the hoses in the new GM style fuel pump, it's hard to get access to the cap(the most ergonomic installation has them lying directly over the cap). I didnt have it fully secured. tightened it down, checked it and its "fuel tight". that tip of slamming on the brakes and then getting out was gold! thanks ya'll!

+1 for the Collective Hivemind

[David T]

+1 for the Collective Hivemind

This forum is the sum total of years of experience by many owners. We have seen it all, it is rare that there is a problem someone never had and a way to figure out and fix it. The hardest ones are when the car has been modified and we don't know all of the details. Electrical problems can be difficult because most owners do not understand electrical systems and if there is a ground problem backfeeds can cause unusual symptoms.