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Discussion Starter #1 (Edited)
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.
 

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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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Discussion Starter #3
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, that’s the hose I was referencing replacing.
 

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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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Discussion Starter #5 (Edited)
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.
 

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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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Did you check the vent hose at the filler tube? I had one crack, and cause a similar issue.
 

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Discussion Starter #9
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.
 

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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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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.
good you did guess that it was that tank seal ... working on the vehicle 1AM is a tough one..
 

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Just to finish this up for the archives -.....

I bet you're finding as a lot of us with this car that dropping the tank becomes just a slight nuisance - after doing it a few times that is. lol


And look at the bright side. Considering all the attention spent on EVAP parts you've got the best operating system in your state!


Thanks for checking back in.
 

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Just to finish this up for the archives -.....

I bet you're finding as a lot of us with this car that dropping the tank becomes just a slight nuisance - after doing it a few times that is. lol


And look at the bright side. Considering all the attention spent on EVAP parts you've got the best operating system in your state!


Thanks for checking back in.
I’m having the exact same problem on my 96 Impala.
I have replaced the switch and the vacuum control solenoid, gas cap, all rubber hoses going to and from them, but I’m not sure how many other hoses can leak due to age, or where they are located.
The hose next to the filler tube is good with no leaks so I’m afraid it’s somewhere in the lines going back to the gas tank, or ones going to the vapor canister.
Would any hoses going to the canister cause the DTC ? Or is that after all the pressure control vapor release mechanisms ?
Thank you 96Black for any help you can offer, you appear to be very knowledgeable about this particular issue, hence my contacting you...
 

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Mr. Chilln -

While Gratifying it only takes a minute to find me out as not nearly so smart as just a well reader and gooder searcher. Well, an I got a FSM, and that dam thing adds 30 IQ points just owning it. As someone who's been sporadically semi-active on this forum the past couple decades I'd have to say cross-combative searching adds more to the smartpool than anything. And set your mind to thinking like a hapless GM designer saddled with slinging together cars with the usual $.25 Chevy engineering budget. That'll stack the deck in your favor for getting in the head of these dinosaurs. You sound like you'e mostly there already.



Cliffs:
-FSM = all of $50 nowadays on ebay = gold in your pants
-Search, crossways upside down, in the morning over coffee when you're brightest
-As for that goofy EVAP, replace all front to back and back to front. When the car got old enough for a few things to start going wonky with it, the design started reminding me of an Escher drawing. By the time you start tracking the system from one bumper it don't make no sense by the time you get to the other one. Just replace all-new componentry and you won't have old parts fighting new ones.

-Most of all, and I even get tired of hearing it myself say it. Spend the hundred or more (ok maybe 2 or 3 hunderd) a year on PM everywhere and save yourself thousands in emotional trauma and aggravation and extended loss of your driver.

-Best Luck
 

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While Gratifying it only takes a minute to find me out as not nearly so smart as just a well reader and gooder searcher. Well, an I got a FSM, and that dam thing adds 30 IQ points just owning it. As someone who's been sporadically semi-active on this forum the past couple decades I'd have to say cross-combative searching adds more to the smartpool than anything. And set your mind to thinking like a hapless GM designer saddled with slinging together cars with the usual $.25 Chevy engineering budget. That'll stack the deck in your favor for getting in the head of these dinosaurs. You sound like you'e mostly there already.

Gotta agree here. The FSM and maybe a Hayne's or Chilton are must haves. I've read so many posts and the stickies. Even though most here any more are big boys with an LT1 I still find lots of info for my little LO5. Thanks Fred.


Cliffs:
-FSM = all of $50 nowadays on ebay = gold in your pants
-Search, crossways upside down, in the morning over coffee when you're brightest
-As for that goofy EVAP, replace all front to back and back to front. When the car got old enough for a few things to start going wonky with it, the design started reminding me of an Escher drawing. By the time you start tracking the system from one bumper it don't make no sense by the time you get to the other one. Just replace all-new componentry and you won't have old parts fighting new ones.

-Most of all, and I even get tired of hearing it myself say it. Spend the hundred or more (ok maybe 2 or 3 hunderd) a year on PM everywhere and save yourself thousands in emotional trauma and aggravation and extended loss of your driver.

I now know what's so big and long. It's your replies. :grin2: Stay the course.

-Best Luck
Mark: Snowman-33
 

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While Gratifying it only takes a minute to find me out as not nearly so smart as just a well reader and gooder searcher. Well, an I got a FSM, and that dam thing adds 30 IQ points just owning it. As someone who's been sporadically semi-active on this forum the past couple decades I'd have to say cross-combative searching adds more to the smartpool than anything. And set your mind to thinking like a hapless GM designer saddled with slinging together cars with the usual $.25 Chevy engineering budget. That'll stack the deck in your favor for getting in the head of these dinosaurs. You sound like you'e mostly there already.



Cliffs:
-FSM = all of $50 nowadays on ebay = gold in your pants
-Search, crossways upside down, in the morning over coffee when you're brightest
-As for that goofy EVAP, replace all front to back and back to front. When the car got old enough for a few things to start going wonky with it, the design started reminding me of an Escher drawing. By the time you start tracking the system from one bumper it don't make no sense by the time you get to the other one. Just replace all-new componentry and you won't have old parts fighting new ones.

-Most of all, and I even get tired of hearing it myself say it. Spend the hundred or more (ok maybe 2 or 3 hunderd) a year on PM everywhere and save yourself thousands in emotional trauma and aggravation and extended loss of your driver.

-Best Luck
Thank you 96 Black for the response and your time.
I am in the process now of doing just as you’ve suggested. I hit everything in the EVAP system I could reach from the top of the engine compartment and gas tank filler end, now I’ve got to take a good look at the line coming from my gas tank fuel pump spigot going to the front of the car, everything underneath in between, and then to the vapor canister itself, if I understand correctly there’s also a rubber hose going to the canister that needs replacing also since if leaking will depresurize the tank.
If I’m wrong about that please let me know since it looks like a biatch to get at.
Once again, thank you for your time, effort and help.
I appreciate it very much !
 

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Discussion Starter #17
I’m having the exact same problem on my 96 Impala.
I have replaced the switch and the vacuum control solenoid, gas cap, all rubber hoses going to and from them, but I’m not sure how many other hoses can leak due to age, or where they are located.
The hose next to the filler tube is good with no leaks so I’m afraid it’s somewhere in the lines going back to the gas tank, or ones going to the vapor canister.
Would any hoses going to the canister cause the DTC ? Or is that after all the pressure control vapor release mechanisms ?
Thank you 96Black for any help you can offer, you appear to be very knowledgeable about this particular issue, hence my contacting you...

The canister and hoses *can* trip that off I am told but as the car I'm working on is a 94, it doesn't have OBD2 and it wouldn't set the same codes. As I said earlier, when we started having gas odor problems with this car to begin with, we shotgunned the canister and surrounding hoses and that solved our immediate problems. The problem that made me start this thread came up considerably later and was confined to the rear of the car.
 

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Discussion Starter #18
Oh, also? Don't forget to replace the canister itself as a bad canister can cause problems. It's still available and inexpensive - there are several out there that are literally the original make one minus the Delco/GM logos right down to the other production molded info. I believe we had the carbon canister and all hoses to it replaced in about 90 minutes, working on the ground under the car.
 

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While Gratifying it only takes a minute to find me out as not nearly so smart as just a well reader and gooder searcher. Well, an I got a FSM, and that dam thing adds 30 IQ points just owning it. As someone who's been sporadically semi-active on this forum the past couple decades I'd have to say cross-combative searching adds more to the smartpool than anything. And set your mind to thinking like a hapless GM designer saddled with slinging together cars with the usual $.25 Chevy engineering budget. That'll stack the deck in your favor for getting in the head of these dinosaurs. You sound like you'e mostly there already.



Cliffs:
-FSM = all of $50 nowadays on ebay = gold in your pants
-Search, crossways upside down, in the morning over coffee when you're brightest
-As for that goofy EVAP, replace all front to back and back to front. When the car got old enough for a few things to start going wonky with it, the design started reminding me of an Escher drawing. By the time you start tracking the system from one bumper it don't make no sense by the time you get to the other one. Just replace all-new componentry and you won't have old parts fighting new ones.
Yep, that's exactly what I plan to do, replace everything associated with the Evap system and not have to think about it again for another 10 years.

The canister and hoses *can* trip that off I am told but as the car I'm working on is a 94, it doesn't have OBD2 and it wouldn't set the same codes. As I said earlier, when we started having gas odor problems with this car to begin with, we shotgunned the canister and surrounding hoses and that solved our immediate problems. The problem that made me start this thread came up considerably later and was confined to the rear of the car.
That's exactly what I needed to know regarding the canister lines, so looks like I'll be digging into that as well.
Thank you and I'm sure it does apply to my car as well.
And yes, I did see the final outcome of the thread starter being the FP 'O' Ring... I've wrestled with that item myself before...
 

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Oh, also? Don't forget to replace the canister itself as a bad canister can cause problems. It's still available and inexpensive - there are several out there that are literally the original make one minus the Delco/GM logos right down to the other production molded info. I believe we had the carbon canister and all hoses to it replaced in about 90 minutes, working on the ground under the car.
I thank you for the excellent advice !
I will definitely replace the canister since it looks like a bit of a pain to do it, and I'm going to be in there doing the rubber vacuum lines.
So I can reach everything I need to do this from underneath the front passenger side of the car ?
Do I need to remove the air dam, inner fender lower attachment panel ?
Care to offer a play by play to get access to the canister on a 96 Impala ? If you don't have the time I understand and will do my own research.
I will most likely go with an ACDelco Genuine OEM replacement, I know there's almost no advantage a lot of the time, but in some cases there are and I don't mind paying the extra money, as long as it's not a crazy amount too much...
Thanks again for your time and effort !!!
 
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