94 FWB Fuel Tank Not Sealing/Holding Pressure - Help/Suggestions Needed - Chevy Impala SS Forum
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post #1 of 37 (permalink) Old 10-26-2018, 04:55 AM Thread Starter
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94 FWB Fuel Tank Not Sealing/Holding Pressure - Help/Suggestions Needed

Getting the car ready for a road trip on Monday, so I'm trying to resolve this as soon as possible. Ever since I installed a new fuel pump in this 94 FWD back in the late spring, the fuel tank has not held vapor pressure - open the tank and there's no 'whoosh' of air, no matter how soon after shutdown. Correspondingly the fuel economy has declined by about a third (which from what I've read here is normal, confirmed by problems we had earlier with some disconnected carbon canister hoses). When I replaced the pump, I replaced the vent/gas pressure hose with Gates Barricade hose specifically intended for this purpose. When troubleshooting this again recently, I replaced the hose with new Barricade hose just in case (per a prior post I made here) and used the appropriate spring clamps just in case - no change. On hot days or when the car was full even without operating, fuel vapors could be smelled around the rear of the car. I've checked and swapped the gas cap with no change. There doesn't appear to be any liquid fuel leaks on the high pressure fuel or return lines.

1. One thing that occurred to me is that perhaps I didn't seat the big O-ring properly when installing the tank or that the O-ring I got with the pump was the wrong size or something. I've located the AC Delco part number specifically called out for the car (G19) as well as the GM part number 14088123 and I'm working on getting one of those to just go ahead and swap it. Anyone have any tips for installing this O-ring? I'm more used to setups where the fuel tank is sealed with a flat gasket or a setup where the O-ring sits in a far more defined groove.

2. Is a fuel-resistant sealant/gasket dressing like Sealall or Permatex PermaShield recommended for use in this application?

3. Are there any other sources for fuel vapor leaks in the back of the car or the tank area? Anyone have any other suggestions?

Rapid help would be appreciated; thanks in advance.

Working on a 1994 Cadillac Fleetwood Brougham...

Last edited by CB700S; 10-26-2018 at 04:57 AM.
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post #2 of 37 (permalink) Old 10-26-2018, 06:42 AM
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You've made no mention of the other half of the EVAP system, so may want to pull maint. on things under the hood like the solenoid, charcoal can, hoses.... Also, I take it all your detail on the Gates hoses includes the one forward of the tank that ALWAYS rots out

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post #3 of 37 (permalink) Old 10-26-2018, 11:41 AM Thread Starter
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94 FWB Fuel Tank Not Sealing/Holding Pressure - Help/Suggestions Needed

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Originally Posted by 96 Black View Post
You've made no mention of the other half of the EVAP system, so may want to pull maint. on things under the hood like the solenoid, charcoal can, hoses.... Also, I take it all your detail on the Gates hoses includes the one forward of the tank that ALWAYS rots out


All the forward evap stuff was replaced with brand new Delco/Gates stuff about a year or so ago; visual inspection shows the carbon canister, solenoid, hoses and everything else we installed at that time is not damaged or disconnected. The only thing not replaced in the front are mounting brackets and the metal lines there.

Yes, thatís the hose I was referencing replacing.

Working on a 1994 Cadillac Fleetwood Brougham...
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post #4 of 37 (permalink) Old 10-26-2018, 05:53 PM
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Quote:
Originally Posted by CB700S View Post
All the forward evap stuff was replaced with brand new Delco/Gates stuff about a year or so ago; visual inspection shows the carbon canister, solenoid, hoses and everything else we installed at that time is not damaged or disconnected. The only thing not replaced in the front are mounting brackets and the metal lines there.

Yes, that’s the hose I was referencing replacing.
I am no caddy guy but on my 96 Impala I had a gas smell rear of car. what I found was GM used a plastic tubing connector that connects to a smaller tubing not rubber hose .. then GM placed a rubber hose over that smaller tubing so it goes thru the rear pass side frame rail then to the canister .

3 lines at the forward portion of fuel tank .. pressure / return / and the vent line that vent line plastic reducer connector is at the support hose section .. that connector broke off so the smell and normally you do get a small puff of pressure.. if the pressure is too high then the canister hoses are collapsed and or the canister charcoal is like a solid brick..
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post #5 of 37 (permalink) Old 10-27-2018, 01:54 AM Thread Starter
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I am no caddy guy but on my 96 Impala I had a gas smell rear of car. what I found was GM used a plastic tubing connector that connects to a smaller tubing not rubber hose .. then GM placed a rubber hose over that smaller tubing so it goes thru the rear pass side frame rail then to the canister .

3 lines at the forward portion of fuel tank .. pressure / return / and the vent line that vent line plastic reducer connector is at the support hose section .. that connector broke off so the smell and normally you do get a small puff of pressure.. if the pressure is too high then the canister hoses are collapsed and or the canister charcoal is like a solid brick..
On the 94 FWB, GM used a similar setup but the connection between the tank and the rubber-covered plastic line was done with a 5/16" ID rubber hose - I found an original junked 94 (that had belonged to a manager at the Arlington Texas plant!) and pulled the tank end of the connection to check it and see what I needed to do on the live 94. I've replaced the rubber hose twice since late spring. I thought I'd posted up pics of the original parts on a thread earlier but I guess not. I cut a couple feet off the tank end of the system to take pictures of it. (Click pictures for higher resolution/size versions.)




IMG_1601


Pull the sheath off the plastic tube and this is what it looks like.

IMG_1602


The tank end of the assembly is clearly 1994 GM rubber hose from the tank fitting to where it fits over the plastic tube - from records found in the donor car, it apparently had an issue at some point fairly early in its life and this whole thing had been replaced:


IMG_1600


The main issue I have right now is that the tank is not building *any* notable pressure or vacuum and all lines appear to still be connected and unobstructed.

Working on a 1994 Cadillac Fleetwood Brougham...

Last edited by CB700S; 10-27-2018 at 02:10 AM.
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post #6 of 37 (permalink) Old 10-27-2018, 09:34 AM
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not how that vapor line is setup on my 96 Impala .. big hose from tank connects to a much smaller plastic tubing .. that smaller tubing runs into the larger rubber hose used as a protective covering around the wheel well. I did have to cut that protective rubber hose to get to that smaller tubing as it is very flexible .used long nose pliers to pull it out a 1/2 inch then using an adapter to go from small to large ..

but this is a 94 caddy so possible not similar as on on my 96 chev.. I am original owner so no one hacked my ride . as built in Texas sept 1995 .
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post #7 of 37 (permalink) Old 10-28-2018, 08:23 PM
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Did you check the vent hose at the filler tube? I had one crack, and cause a similar issue.

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post #8 of 37 (permalink) Old 10-28-2018, 08:25 PM Thread Starter
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Did you check the vent hose at the filler tube? I had one crack, and cause a similar issue.


No, didnít think of that - forgot that on this car the vent hose is separate.

Working on a 1994 Cadillac Fleetwood Brougham...
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post #9 of 37 (permalink) Old 10-30-2018, 04:22 PM Thread Starter
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Just to finish this up for the archives - all the hoses turned out to be fine, the problem turned out to be an O-ring that had popped out of its groove without me noticing during the pump install at 1AM. Install ended up leaving the tank not sealed. We were very careful with the replacement and it seems to have solved the problem.

Working on a 1994 Cadillac Fleetwood Brougham...
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post #10 of 37 (permalink) Old 10-30-2018, 05:42 PM
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That o-ring that seals the round pump/sending unit cover on the top center of the tank is a beast to get on right and without leaks.
Glad you got it fixed...

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