Gas tank vent?

[DMC3165]

Where do our gas tanks vent from? I've been having a persistent problem with my fuel pump boot popping off since day 1. I always thought it was do to an improper installation but it has been done at least a half dozen times and not all by me.

The reason I ask tis is today I was using the car most of the day and the tank was full right from the start. By the end of the afternoon I started to smell gas from the tank area. So I went home to see if the boot had popped off again but to my surprise it was tight. However the top of the tank was wet with gas.

My only theory at this point is the tank is not venting properly and the hot gas is pressurizing in the tank? If its as simple as replacing the gas cap I'll try that first. But would like some forum feedback first.

Thanks

[Ron]

It is a closed system...

I'd dry it off and see if you can catch it leaking. I'm guess you've tried before...like watching for water to boil. Baby powders can help you find the trail.

[stevedmc]

Check your connections from the tank to the filler cap. I had a cracked hose that was causing fumes/fuel to vent and leak. I brought the cracked hose to Autozone, showed it to them, and they replaced it for a few dollars.

[Elvis]

which cover for the fuel pump do you have ?
the original one or the new one ?

I got it from Ed Uding, I guess it's a good and improved product from DMCH.

AND the fuel pump has to sit deep enough so that it doesn't push the cover up.
106684 FUEL PUMP COVER SEAL
http://www.delorean.eu/catalog/index.php?cPath=19_25_48

click on #1 and check out how the new cover looks like.

It solved the problem on my car last year.

[stevedmc]

which cover for the fuel pump do you have ?
the original one or the new one ?

I get my fuel pump covers at the dollar store. You can get about 20 bags, i mean covers, for just two or three dollars.

[aludden]

I get my fuel pump covers at the dollar store. You can get about 20 bags, i mean covers, for just two or three dollars.

Are you putting pooper scooper bags? :)

[dustybarn]

The fuel tank vent is connected to the carbon canister. If the hose leading to the canister is blocked, the canister itself is plugged, or the canister vent outlet is plugged (by, perhaps, a wasp nest or something) the tank vent system won't work properly and vapor pressure may build up in the tank.

[Rich]

++ on dustybarn's system description. With the fuel pump boot in place along with tight connections at the filler neck you should not see any raw gas - ever.

The boot's not designed for pressure or vacuum.

Is the vapor vent clear? Check it upstream and downstream at the connection in the engine bay. The metal vent tube pops up near the left frame member near the firewall where it connects to a black hose connected in turn to the charcoal canister inside the left pontoon. Break in here. With the fuel cap off you should have open flow through the tube toward the tank. Then check for open flow back through the hose to the canister regardless of the fuel cap.

Photo here shows the vapor hose leading forward from the canister toward the vapor vent tube that runs forward to the rollover valve near the top of the filler neck.

7447

[stevedmc]

Are you putting pooper scooper bags? :)

Gallon size zip lock bags.

[Ron]

You guys have all of this backwards...

It is a closed system -- If the vent hose is plugged, it will not cause vapor leaks -- it can cause the tank to collapse!
If you have a port on your canister that has nothing on it thinking it is a vent, buy a blanking cap from DMCH(#12) (http://http://store.delorean.com/c-275-2-4-0-evaporative-control-systems.aspx)

Read D:06:01 thru 03 in the Workshop Manual (Page 40 in this pdf file) (http://dmctalk.org/attachment.php?attachmentid=592&d=1306869922).

(Not Steve, he has a carb...but he knows where to stick it ;-)

[DMC3165]

I seem to only have a gas leak when hot. So my thinking was a bad vent or cap was not allowing the vapors to escape and pressure was building inside the tank. Wether or not my logic was accurate or not is something else but I figured it was a place to start.

The only thing that's got me today is the boot was still tight. Which now makes me think the top of the tank maybe cracked? This is my second boot and cover in under 2 years. The first one popped off several times and I got so disgusted with it I had Rob Grady replace it again with a new boot and that popped off as well. So I reassembled it again and everything's in place but where's the gas coming from?

Perhaps it's a small crack due to over tightening and hot vapors escaping through it? I really don't know its just been driving me up a wall.

[David T]

Pull the cover boot and see if there is any fuel around the fuel pump.
David Teitelbaum

[Rich]

I seem to only have a gas leak when hot. So my thinking was a bad vent or cap was not allowing the vapors to escape and pressure was building inside the tank.....So I reassembled it again and everything's in place but where's the gas coming from?

You are doing the right thing in not giving up on this. Fuel leaks are serious in any car.

If the boot is tight now then check the tank itself, as you propose, also the filler hose and all connections at the tank.

Pressurized or not, the fuel tank and fittings should never leak. And it's not designed to pressurize no matter how hot the fuel might be.

[David T]

Actually the tank will pressurize a little when hot. The fumes are supposed to be collected in the vapor canister when the motor is not running. When you start up the motor the valve to the canister is opened and the fumes are sucked into the motor to be burned. Another thing to check is the hose that comes out of the bottom of the vapor canister and comes out the bottom of the left, rear, pontoon. It seems to be a favorite spot for insects to go into and plug up. Make sure all of the hoses are still connected in the vapor system. On a lot of cars they get disconnected and you don't notice until you smell fumes on a hot day. The fuel boots are the most likely cause though. Especially if you notice it after you fill up.
David Teitelbaum

[stevedmc]

(Not Steve, he has a carb...but he knows where to stick it ;-)

That's right. Steve has a carb and zero fuel system problems.

[sean]

That's right. Steve has a carb and zero fuel system problems.

After how many fuel pumps?

[stevedmc]

After how many fuel pumps?

I've replaced zero fuel pumps since running a new ground connection to the fuel pump. I suspect the ground issue was part of my K-Jet problem as well. A ground issue will cause problems with any fuel pump.

[sean]

... since...

nice job Bill...I mean Steve.

[Ron]

I've replaced zero fuel pumps since running a new ground connection to the fuel pump. I suspect the ground issue was part of my K-Jet problem as well. A ground issue will cause problems with any fuel pump.It's always those pesty grounds.

[EdR5150]

Where do you run it? The front crumple tube? What gauge wire?


I've replaced zero fuel pumps since running a new ground connection to the fuel pump.

[stevedmc]

Where do you run it? The front crumple tube? What gauge wire?

I ran a ground wire directly from the battery to the fuel pump. I don't recommend doing this because it bypasses the inertia switch. I did this temporary fix because I was in a bind and needed to make sure my fuel pump didn't have any ground problems for the 10+ hour trip to Sean's house a few months back.

I'm not sure what gauge the wire is. It is just some spare wire I had laying around from when I rewired 12v to my radio. I wouldn't recommend doing what I did, since my ground connection is for testing purposes only. When I get around to it I'm going to remove it and install a full ground bus similar to what Captain Carburetor has done.

As I've said over and over, don't do what I did. I'm not married, don't have a girlfriend, no kids, and frankly, I don't value my life. If my parents weren't alive to worry about me, I would own a motorcycle.

[EdR5150]

I don't recommend doing this because it bypasses the inertia switch.

I thought the hot wire would run through it... does the ground really run through the inertia switch?

[sean]

does the ground really run through the inertia switch?

Yes. Schematics can be seen here:
http://dmctalk.org/showthread.php?40-All-Wiring-Schematics

[Bitsyncmaster]

I thought the hot wire would run through it... does the ground really run through the inertia switch?

Yes all the pump current goes throught the switch. It should have been wired to the RPM relay so no current would pass throught the switch.

[DMC3165]

Just to follow up on this quick. If there is a problem with the charcoal canister, would that kick on the Lambda light? Not really sure about a car from this vintage but other cars with emission controls would usually trip a check engine light if something like that happens.

[dustybarn]

Just to follow up on this quick. If there is a problem with the charcoal canister, would that kick on the Lambda light? Not really sure about a car from this vintage but other cars with emission controls would usually trip a check engine light if something like that happens.

No. Cars in 1981 had nowhere near as sophisticated onboard diagnostics as cars do now. The Lambda light comes on when the Lambda counter counts enough miles. The oxygen sensors of the time had poor durability and the only way to make the cars pass emissions standards was to enforce replacement of the oxygen sensor every so often. Chevrolets of the same time period had a mechanical red flag that would drop down in the odometer window to tell you to replace the oxygen sensor. AFAIK on the D there is no direct diagnostic capability with respect to the evaporative emissions system.

[DMC3165]

I've still been having periodic trouble with this. But I noticed today after an hour drive my gas cap had alot of pressure under it. When I pulled it off and restarted the car I could see gas vapors bellowing out the gas fill.


I checked my canister and all the lines are clear the inside of the canister seems ok no obvious obstructions anywhere. I did notice the small line to the left of the canister was difficult to blow into. But I still don't think this is my problem.

Gas smell at times is horrible. Comes right in where the shifter boot is. Hopefully I won't blow myself up one day with this thing.

[David T]

I would check the vent hose that runs from the gas tank to the cannister to make sure it is hooked up, not blocked off or kinked.
David Teitelbaum

[DMC3165]

What is the roll over valve for and is it a check valve?

[Ron]

What is the roll over valve for and is it a check valve?

See page 85:
http://dl.dropbox.com/u/13720563/DeLorean%20and%20Volvo%20Manuals/DMC-Technical-Hybrid.pdf

[DMC3165]

If it is jammed or not workkng properly. Would that block the flow of vapors to the canister and could it cause my fuel tank to pressurize?

[Ron]

If it is jammed or not workkng properly. Would that block the flow of vapors to the canister and could it cause my fuel tank to pressurize?
Contrary to several posts in this thread, it is a closed system -- It is supposed to pressurize!
To answer your question, it's possible but very unlikely. But more important, if the roll over valve, its hose from the tank, the vent tube, or hose connecting it to the canister is stopped up, it can cause the tank to collapse. Normally the system "vents" both ways, vapors to be burnt when a purge signal (vacuum) is sent to the canister, and, allows air to enter the tank to replace the space occupied by fuel as it is consumed (to prevent it from collapsing), but, ideally, NEVER to the atmosphere.

Take another look at the link I posted above, (here is a better diagram http://store.delorean.com/c-275-2-4-0-evaporative-control-systems.aspx ). Follow the vent path (from filler to canister) and make sure all are clear, bbut don't leak. Check the orifice in the cold start valve air tube and other things mentioned on the following pages while you are at it... If you haven't double checked the boot, as David suggested, I would, while you can smell the fumes...

[kings1527]

Was there any followup or solution to this thread? I'm having the exact same problem. Tank pressurizes when the tank is maybe 1/2 full or less and vapors are coming out of the fuel cap (which I know is good) and eventually through the air vent and stinking the cabin.

Things I know are good is the check valve, vacuum lines are clear, carbon canister appears to be ok and has a blanking cap on it. All vacuum connections appear to be tight but I'll confirm vacuum is coming from the line going into the engine underneath the W pipe. I do have Hervey's silicone vacuum lines on my car and I'm not sure if something weird like the diameter is off but I'm trying to think of everything.

I wouldn't mind bypassing the carbon canister by joining the two vacuum lines together and double checking to make sure that's not the problem. But for a pretty simple layout, I can't figure out the issue.

[DMC3165]

Was there any followup or solution to this thread? I'm having the exact same problem. Tank pressurizes when the tank is maybe 1/2 full or less and vapors are coming out of the fuel cap (which I know is good) and eventually through the air vent and stinking the cabin.

Things I know are good is the check valve, vacuum lines are clear, carbon canister appears to be ok and has a blanking cap on it. All vacuum connections appear to be tight but I'll confirm vacuum is coming from the line going into the engine underneath the W pipe. I do have Hervey's silicone vacuum lines on my car and I'm not sure if something weird like the diameter is off but I'm trying to think of everything.

I wouldn't mind bypassing the carbon canister by joining the two vacuum lines together and double checking to make sure that's not the problem. But for a pretty simple layout, I can't figure out the issue.

Way to resurect an old thread! I sold the car two years ago. But what I can tell you is the tank itself was the problem. Upgrading to the DMV improved fuel pump (modified AC Delco unit) helped alot because the original style would keep popping out. Assuming it was an over pressurized fuel tank causing this problem is what started this thread. In my case the tank opening where the fuel pump sat was slightly deformed and would constantly leak and eventually the fuel pump would just pop out. What was weird when the tank was full you'd never smell anything only when it was around half or less and when it was hot outside it was even worse. I never got around to totally fixing it but a new tank or a ton of silicone might have solved it.

[David T]

Read my post #14. Also you could have a bad gas cap or even a wrong one. First place to look is the inner pump boot to see if fuel is pooling on top of the fuel pump. Make sure the fuel sender unit is not leaking also.