Gas vapor smell while driving.

[QuadcityDMC]

Is it normal to have gas smell from the gas tank cap after driving for awhile? With the windows rolled down I can smell it in the car. I know the tank has to breath out the vapor but I though there was a vapor hose that ran to the back left body tube.

After driving I can unscrew the gas cap and the sound stops, but when I screw it back on I can here gas vapor start to hiss out the top of the cap.

[stevedmc]

Is it normal to have gas smell from the gas tank cap after driving for awhile? With the windows rolled down I can smell it in the car. I know the tank has to breath out the vapor but I though there was a vapor hose that ran to the back left body tube.

After driving I can unscrew the gas cap and the sound stops, but when I screw it back on I can here gas vapor start to hiss out the top of the cap.

Check your hose connections going from the tank to the filler cap. I had a vapor hose that was completely snapped causing the same problem. I took the hose into AutoZone and they were able to fix me up with what I needed.

[sean]

Time to pull the fuel pump access panel. Make sure you don't have any leaks at the fuel pump boot.

[DMCMW Dave]

Is it normal to have gas smell from the gas tank cap after driving for awhile? With the windows rolled down I can smell it in the car. I know the tank has to breath out the vapor but I though there was a vapor hose that ran to the back left body tube.

After driving I can unscrew the gas cap and the sound stops, but when I screw it back on I can here gas vapor start to hiss out the top of the cap.

There is a vent hose that goes from the tank to the rollover valve (located next to the filler, you can't see it without taking off the cover plate). I've seen that hose get crimped by the cover plate.

If that hose is crimped, or the rollover valve was to stick closed, pressure would build up in the tank (from heat) and pressurize the tank (the excess pressure is supposed to be vented to the carbon can in the left rear pontoon and burned by the engine). If the tank gets pressurized the next best place for the fumes to vent is probably the fuel pump boot, which happens to be located right next to the drain hole for the windshield which also feeds directly into the air intake for the heater/airconditioner.

[Jonathan]

Sounds like Dave and the others have given you the whereabouts on the vent hose, but to answer your question of "is it normal to smell fuel in the car?" and I would say no. I don't smell fuel at all in my car even right after filling up. I think if you sort out the vent line blockage, you won't smell fuel either.

[sdg3205]

Avoid "topping off" too.

[Nicholas R]

Make sure your sending unit cap is tight, very tight. I drove around with that smell for a few years, turned out my cap was just dirty and wasn't compressing the fuel sender gasket so when the gas would slosh around, it would leak out there.

[David T]

All of these are possibilities but the most common problem is the boot holding the fuel pump has deteriorated and is leaking and is full of fuel. Once you remove the access cover and the cover boot you will know right away what the problem is. It is NOT normal to smell fuel and you should investigate, determine the problem and fix it right away. Bet it only is noticeable when you have 1/2 tank or more of fuel!
David Teitelbaum

[xbrules]

Ignorance can be bliss on occasions, I went for a look at my fuel system just now hoping that my breather had perished.... only to discover my fuel pump is leaking under pressure... just magic... well that answers that question, and also explains my lousy fuel consumption...

[Rich]

After driving I can unscrew the gas cap and the sound stops, but when I screw it back on I can hear gas vapor start to hiss out the top of the cap.

OK, that last bit tells us that your fuel tank/filler is pressurized at least some of the time. That is abnormal all by itself.

++ See Dave's post #4. Your charcoal canister vent hose and the fuel filler neck should have a direct and normally-open connection, one that prevents pressurization of the tank. A simple air flow test from the canister connection forward with the fuel cap off will verify satisfactory venting or troubles from blockage.

The pressurization suggests that your fuel pump boot and the filler hose atop the tank are intact, otherwise the tank would vent at those connections. If you leave it pressurized long enough you may damage the fuel pump boot. It's not designed to hold significant pressure. Reason enough to remedy the situation, to say nothing of the safety issue of gas vapors around - or in - the car.

[DMCVegas]

++ See Dave's post #4. Your charcoal canister vent hose and the fuel filler neck should have a direct and normally-open connection, one that prevents pressurization of the tank. A simple air flow test from the canister connection forward with the fuel cap off will verify satisfactory venting or troubles from blockage.

Umm, yes and now. Quick and dirty explanation:

When the car is at rest the Charcoal Canister collects fuel vapors from the fuel tank. There is then a tube that connects to the Intake Manifold, BUT there is a diaphragm controlled valve that keeps that particular tube closed while the engine is at rest. Once the engine starts, vacuum will be applied to the diaphragm causing it to open. Engine vacuum then takes over and evacuates the accumulated fuel vapors from the Canister. The only difference between older cars like the DeLorean and any modern one is that the vacuum line has since been replaced with a solenoid valve.

So yes there is a constantly open tube, but ONLY when the engine is running.

HOWEVER it should be noted by everyone that Canisters can in fact malfunction if exposed to raw, liquid fuel. They will clog up and prevent the unit from purging once the engine starts. This is key to maintaining the fuel pump as well as to prevent vapor from leaking out. I've had this same problem with my own DeLorean. I replaced the Charcoal Canister and it went away. I also had a Jaguar XJ6 that had this EXACT same issue. Fuel pump would buzz, and there would be a strong smell of gas at the back of the car. Pop the cap off and you would hear the pressurized vapor escape and then the car would be quiet again. Hell even at my last job we had a memo sent out about this same issue. Lots of field techs were complaining that their trucks had strong gasoline smells. They ended up dropping several thousand dollars at the local Ford dealer to get all those canisters replaced because the techs were topping-off and causing liquid to contaminate the charcoal canisters.

You don't normally see this issue with cars simply because the fuel cap is aft of the windshield, so the vapors simply get blown away. But if you're ever stuck in traffic and are nowhere near any gas stations and smell that strong sickly-sweet hot petrol vapor, you know that someone's car around you has a failed charcoal canister. Even California has since taken to testing these components since ODB-II can't detect the problem. The DeLorean is excluded of course because our canisters are not readily accessible for testing.

If you're ever wondering if you've got a bad Charcoal Canister and want to test it, it's simple, but it's best done on a hot summer day.

1. Remove your gas cap. A little pressure hissing is normal. But if it sounds like a deflating balloon, you've got a problem.

2. Disconnect the Vacuum Hose, then plug it up. Connect a hand-held vacuum pump to the Canister and start pumping, You should see a change in the engine's RPMs right away. If not keep pumping. Apply enough pressure to get the valve to crack open. Once it does you'll hear the engine go crazy as the LAMBDA system goes haywire trying to adjust the fuel mixture. This method will tell you if it's just the diaphragm that's bad, but either way you're going to be replacing that canister since it's a non-serviceable part.

[WelmoedJ]

2. Disconnect the Vacuum Hose, then plug it up. Connect a hand-held vacuum pump to the Canister and start pumping,

Call me stupid, but....
The canister has three vac lines, which one you refer to for disconnection?
Which of these lines you intend to use to crack open?

Or do you mean "take out the canister and then test?
But even then which are the connections to use?
And what does one do with the remaing connections/lines ("plug the vacuum hose")?

Thanks for explaining.

[jawn101]

Make sure your sending unit cap is tight, very tight. I drove around with that smell for a few years, turned out my cap was just dirty and wasn't compressing the fuel sender gasket so when the gas would slosh around, it would leak out there.

+1 here, I had a bad gas odor as well and this was my problem. The gasket has a notch that must line up with the tank as well as the sender, and whoever installed mine last did not line them up. Small amounts of gas were sloshing out and the smell was pretty strong. Removing the sender, cleaning up the mess and reinstalling it with a proper seal eliminated the odor completely.

[David T]

Before going through a lot of testing check the vent hose that comes out of the bottom of the vapor canister. I see them plugged up with insect cr-p all the time. Stick a wire up inside. The hose should be sticking out of the bottom of the driver's side pontoon. If it isn't you will have to open the pontoon and route the hose properly. I would still start at the fuel tank and check all of the components there first. A little pressure is normal on the tank, especially if you park it outside and the car gets hot.
David Teitelbaum

[QuadcityDMC]

I took that cover off today and found nothing twisted or bent. No fuel leakage around the tubes. Is it possible that I might have a bad seal on the gas cap?

I did find a hole in the body tube, looked like someone tried to add another trunk cable and drilled into the back of some wires but stopped short.

[David T]

You should at least remove the cover boot and make sure there is no fuel in the pump boot. If everything is nice and dry you will have to look elsewhere. Make sure the tank sender is sealed. If all of that is good you will have to follow the vent hose to the vapor cannister to make sure it is not kinked, blocked, or cut.
David Teitelbaum

[QuadcityDMC]

I took the "vapor" hose off the roll over valve and to the carbon can out to see if any thing was up with it.

http://a3.sphotos.ak.fbcdn.net/hphotos-ak-ash3/540219_421638671195989_100000495801550_1670705_102 5191428_n.jpg

http://a1.sphotos.ak.fbcdn.net/hphotos-ak-ash3/563752_421638937862629_100000495801550_1670706_214 5099409_n.jpg

This is what it looked like when i took it out, the bottom was off and a hose was not connected. I took the hose to the tank off and checked it. It was clear but I did cut the hose off at the 90 because it was leaking through the hose.

I connected all the hoses back and but the bottom on the carbon can. Checked fuel pump boot, which has new DMCMW hoses. I will have to drive around and check again if there is any leaking from the pump. Gas tank is 1/2 right now.

Going to order a new gas cap also.

[jawn101]

I took the "vapor" hose off the roll over valve and to the carbon can out to see if any thing was up with it.

This is what it looked like when i took it out, the bottom was off and a hose was not connected. I took the hose to the tank off and checked it. It was clear but I did cut the hose off at the 90 because it was leaking through the hose.

I connected all the hoses back and but the bottom on the carbon can. Checked fuel pump boot, which has new DMCMW hoses. I will have to drive around and check again if there is any leaking from the pump. Gas tank is 1/2 right now.

Going to order a new gas cap also.

Well time and your checks will tell, but I'd be willing to bet you found your problem. I didn't know the bottom could come off the canister. I wonder if it might be up for replacement, but others may have more info than me on that.

[David T]

The bottom comes off so you can get to the filter to replace it.
David Teitelbaum

[jawn101]

The bottom comes off so you can get to the filter to replace it.
David Teitelbaum

Learned something new today. I didn't know it had a replaceable filter, I thought the whole canister was a sealed throw-away unit. Good to know!

[lazabby]

I had my cannister out last night in order to re-route some hoses. I notice that there is one barb not used and the lettering next to it reads "Carb Bowl". The parts manual indicates that the barb should be plugged. I noticed that my cannister was not plugged at that barb so I plugged it. How is the performance of the car affected if that barb is left unplugged? Are gas fumes more likely to leak?

[David T]

On just about every car I see there is a rubber cap on that port but it is so deteriorated that it doesn't seal anymore. Doesn't seem to have any noticeable effect. That port is most likely meant to capture vapors from the fuel bowl of a carburetor when the motor is not running. Not used in our application. Just get a nice rubber cap for it.
David Teitelbaum

[DMCMW Dave]

On just about every car I see there is a rubber cap on that port but it is so deteriorated that it doesn't seal anymore. Doesn't seem to have any noticeable effect. That port is most likely meant to capture vapors from the fuel bowl of a carburetor when the motor is not running. Not used in our application. Just get a nice rubber cap for it.
David Teitelbaum

I completely agree. I see that cap rotted off all the time and have never noticed it causing any ill effect or gas smells. Since it's meant to be a carb bowl vent the air volume being pulled in would be very low.

[Timeless]

Learned something new today. I didn't know it had a replaceable filter, I thought the whole canister was a sealed throw-away unit. Good to know!
I recently removed the charcoal canister in my D to inspect since I am getting an occasional faint fuel smell while idling with the windows down. The filter in the bottom had to be original - it was gross. Installed a new filter and will continue to investigate the smell. No visible leaks anywhere, new DMCH fuel cap last year, rollover valve and related hoses seem to be intact. Sending unit cap seems tight - running Delphi modern pump kit w/EFI.

[dn010]

I have EFI as well as the modern fuel pump. The only time I smelled fuel at idle was when one of the accumulator hoses started to leak. I would love to dump that useless thing but am too lazy to go through the trouble removing it and dealing with all the plumbing.

[Timeless]

I have EFI as well as the modern fuel pump. The only time I smelled fuel at idle was when one of the accumulator hoses started to leak. I would love to dump that useless thing but am too lazy to go through the trouble removing it and dealing with all the plumbing.
Agreed. Next time the car is on the hoist I'll check that. I paid to have the accumulator bypassed as part of the EFI conversion and they (DI liars) didn't do it.

[Bitsyncmaster]

Agreed. Next time the car is on the hoist I'll check that. I paid to have the accumulator bypassed as part of the EFI conversion and they (DI liars) didn't do it.

You really don't need to remove the fuel accumulator with EFI. Only reason to do do is to eliminate it's failure of it or the lines. EFI runs lower pressure around 50 PSI and the accumulator evens out the PSI pulses of the fuel pump.

[dn010]

Only reason to do do is to eliminate it's failure of it or the lines.

This is my goal one day. After 40+ years, I doubt mine is even operational.

[Timeless]

UPDATE: after replacing the filter and a long drive with the windows down, no smell! Also installed a new hose that was missing from the bottom of the canister and routed it through the hole at that bottom of the body tub.