Slight fuel smell in cabin, wet gas cap, vapor lock at pump

[jawn101]

Thread title sort of says it all. My fuel system is completely overhauled, recently. I also have a NOS non-locking gas cap from Houston, since my locking one kept seizing up and I didn't have the energy to rebuild it it for a 4th time.

When I gassed up this morning, the pump nozzle kept locking up on me. I had to hold it at an extremely slow flow rate to stop that happening. That has only started happening recently; the issue had previously gone away when I installed the new Houston pump/sender combo.

When I got home from our tech day, I noticed a slight fuel smell in the cabin. When I got out of the car, there was no fuel odor - so it wasn't from the motor, etc. I took off the gas cap and the odor got stronger. I also noticed the underside of the cap (the rubber seal area) was damp with fuel.

Why would these things be happening? Any ideas what I should check?

[Jonathan]

When I did some fuel system overhaul work and then noticed a couple symptoms similar to yours, it turned out I did not have the fuel pump boot pushed all the way down. It seemed like it was all the way in but it still had another inch to go. It was only after having issues with the gas station pump clicking off and then subsequently overfilling it all over the map that I realized you really need to push down on the pump assembly to get it fully seated in the opening in the tank.

[jawn101]

Interesting. That was all fine recently but maybe something's shaken loose. Were you dealing with the new combo unit as well? I'll check that when I get a chance :)

[Jonathan]

No combo unit for me. I had actually just raised the original style pump assembly out of the hole while I was replacing the two short hoses that connect to the hard lines. I don't know for certain whether the combo unit has the same rubber boot as the original so maybe this isn't a possibility for your problem.

[jawn101]

Yeah it's a very different design. No boot. But perhaps the clamp holding the unit in place is loose. Worth a look anyway. Unless anyone else has other ideas!

[DMC5180]

Fuel splash or accidentally overtopping the neck will cause that smell too. But it goes away after it evaporates.

[jawn101]

Yeah, of course. No splash here though, and the smell was hours after filling up. The nozzle shut off issue was first thing in the morning.

[sdg3205]

Are the lines to the carbon canister clear? If the venting isn't working properly you'd smell fuel.

I have found I need to pump fuel slowly in the Dmc than other cars. I just figured it was the physics of the set up.

[jawn101]

I'll check that as well. I did remove the carbon canister when I did a water pump recently so maybe something got knocked loose.

The really baffling symptom is the bottom of the fuel cap being wet though.

[Jonathan]

When I had my problem with the pump assembly and boot not being all the way down, it had left a small opening for air or fuel.

When pumping gas at the station, it kept clicking off because (I think) it didn't get the expected back pressure. So as I went slow, I overcame this shut off issue, but then when it needed to click off, it still didn't create the needed back pressure because that last two litres or so when up over the edges of the tank opening and down around the frame and absolutely all over the place under the car. Not fun as you can imagine. It all turned out fine as I finally realized it wasn't pushed all the way down.

What could go in the stupid comments thread from that episode was the crusty old guy that asked me if I needed anything and as I said no, I'm ok, thanks, he's says 'no, I was wondering if you wanted a match?' Another one of those 'what the hell is wrong with people' might-as-well-leave-the-car-at-home comments.

[jawn101]

Lol, I had that same experience with a popped off boot causing a ton of fuel to dump under the car. It was ultimately the last straw that led to me getting the combo unit in the first place.

[Rich]

Yeah, of course. No splash here though, and the smell was hours after filling up. The nozzle shut off issue was first thing in the morning.

Since it's warm there again, Jon, any chance you can do a simple "tank pressure test" and also check for fuel odor today? If all is well the only place for fuel vapors to come out is thru the carbon canister - without odor.

With the car and fuel at garage temperature pop the fuel cap to be sure there is no tank pressure to start with. Then go for a nice drive to get the fuel warmed up. Maybe 20 minutes or more?

Then stop the car in some quiet place, check again for fuel odor in whatever conditions you noticed odor before. Just after that take off the fuel cap while listening for any signs of hissing or pressure relief at cap. There should of course be no odor and no hissing or pressure at any time.

The idea is to see if the fuel odor is from a leaky line (liquid) or from the upper part of the tank or the plumbing above the tank (vapor). I guess a search for dripping fuel might be in order while you're at it - if not done already.

[jawn101]

Hmm, good ideas Rich. I'm not near the car today but that's something I will try this week. Never noticed any liquid fuel anywhere (apart from the underside of the cap anyway) and the odor isn't strong enough to be that, IMO. But I will be removing all the inspection covers under the bonnet and doing some poking around and testing to see if anything looks off. I'm really hoping something simple has just come loose, like the big retaining clamp for the pump assembly.

[David T]

Hmm, good ideas Rich. I'm not near the car today but that's something I will try this week. Never noticed any liquid fuel anywhere (apart from the underside of the cap anyway) and the odor isn't strong enough to be that, IMO. But I will be removing all the inspection covers under the bonnet and doing some poking around and testing to see if anything looks off. I'm really hoping something simple has just come loose, like the big retaining clamp for the pump assembly.

Working on the fuel pump and it's boot should have nothing to do with the filling of the tank. The fuel odor can be because of:
Leaky fuel level sender
Leaky fuel pump boot (the inner one)
Leaky connections to the fuel pump
Plugged vent hose
Leaks at the fill pipe or the roll over valve
Check the vent hose coming out of the bottom of the vapor canister. One one car I found it ALL plugged up with insect debris preventing it from venting. Most Deloreans will not fill properly if you put the nozzle all the way on. The pump fills the tank too fast and it backs up in the fill hoses and shuts the nozzle off. If you always get fumes try not filing it ALL the way up.

[jawn101]

Just returned home for the evening and took a quick feel under the LH pontoon. I definitely did neglect to route the charcoal canister venting hose out to the open air. Makes me wonder if I put it back with anything else disconnected. These troubles did start around the same time as my recent water pump install (which was also the last time I R/R the canister) so this sorta makes sense. I will fix that whole assembly up tomorrow and report back. At least that's a really easy job. Fingers crossed.

[jawn101]

So an update. I re-routed my charcoal canister exhaust pipe outside of the car. I started up the motor and checked all around the FD, CSV, CPR and FV for leaks. No liquid. Removed the inspection panels in the boot and checked the filler neck and feed/return lines to the pump as well as the level sender blanking plate and the seal of the pump itself. No liquid here either. No fuel smell with the engine running, unless I removed the filler cap. Cleaned the filler cap rubber seal and went for a ~20 mile drive like Rich suggested. Had the HVAC on vent/max fan the whole time to see if I detected any odor inside the cabin. I didn't. When I returned home I checked again for liquid fuel and didn't see any. Checked the cap and there was no liquid there either.

I am cautiously optimistic that the issue was that vent hose, but this wasn't a 100% scientific test. I still had the inspection panels off during my drive, which provided extra airflow around the tank/pump/filler area. It's also much cooler today than it has been recently, only 70. So there were some unaddressed variables.

I will keep an eye on things. Maybe this weekend I will tear around a little more and then go gas up, see if the pump shut-off issue is also resolved.