greenyone

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I noticed a whining noise under my hood today after I parked the car in the garage. It was difficult to pinpoint where it was coming from but I finally found the source to be in the vicinity of the vapor canister. I pulled the line that leads back to the tank and it got louder. There was suction through that line causing the noise. So I cracked the gas cap to equalize the pressure in the system and the noise stopped. Is this a tell-tale sign that the canister is bad? Or could something be wrong with the solenoid or something else?

RBob

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Are you sure it was suction and not pressure? Suction from the tank shouldn't affect the vapor pressure control valve. But pressure from the tank will push it open to allow the fumes into the canister.

As hot as it is out there my bet is that there was pressure in the tank and all is well. The system is working as it should.

RBob.

greenyone

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Yes. I stand corrected. It was pressure not suction. I performed all the tests in my service manual. Everything checks out with the evap system components and the tank vent valve in the drivers wheel well (which I took apart and cleaned even though it was opening and closing at about 7psi.) Strange though. My 1991 service manual (GM manual not Haynes) does not even show the valve in the wheel well. It actually has a diagram that shows and describes a vented fuel cap with no mention of that valve in the wheel well. But it's clearly there on my car.

Bob88GTA

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I just posted this earlier on anothe post.
I happed to drive my 85 yeasterday. It was 98* here. I drove 20 miles to my home and the car was just running poorly. I pulled in the garage, got out and heard the same thing. Gurgling, gas smell and all. I did not here the little tank vent by the rear end making any noise. I went to take my gas cap off and it was sooo pressurized/or under vacuum, the the cap turned about 1 full turn till it started to vent. I could not get it off. I left it vent over the next hour or so and finally I was able to fully remove it. Its obvious there's a problem with my vent/and canister. Need to check that out.
There are so many threads on this. I wish this could get figured out. Good luck!

greenyone

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Agreed. This may be the most perplexing of all the thirdgen issues. Nobody seems to be able to diagnose it an nail down the exact problem. It's like a crap shoot of throwing parts at the car until it's resolved.

thtanner

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There is the plastic valve that's attached to the tank. That should prevent the tank from getting a negative pressure. If you're getting negative pressure, I'd start there. Vented caps also do the same thing (vent IN, not OUT) if yours is bad and you can't clean/replace it.

Check operation of the in-line plastic valve that's before the evap canister. They can get clogged/fail closed.

Could clean out the hard fuel/return/evap lines with some compressed air as well.

You should be able to blow freely through the evap canister's inlet. If you can't, it needs to be replaced (unless its the serviceable kind, then just swap the padding inside)

I have read of failing fuel pumps causing extra heat and pressure.

greenyone

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Like I said. I performed all of the service manual checks. The canister flows freely as does the valve when a couple psi of vacuum is introduced via a hand pump. Same goes for the tank vent valve. It flows freely when around 6-7 psi is introduced. I'm starting to have a feeling that something in the tank is the culprit. I've read that there is a check valve internal to the sending unit assembly that can cause issues. I have not investigated that thoroughly yet though. I did blow compressed air through my vent line using the open end under the hood as the air inlet. It flows through freely with the gas cap off.

thtanner

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I'd probably drop the tank and swap pumps for the heck of it at that stage.

greenyone

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That bring up another question. Which fuel pump do you guys recommend for a TPI engine? I see so many mixed reviews on all the brands from Delco, Bosch, Delphi, Walbro etc..

thtanner

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I threw my Walbro in the trash. Excessively loud for no reason.

305 uses the ACDelco EP241. I have the EP381 (since I have the 350) and have had no issues. Nice and quiet.

greenyone

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Hmm. Rock Auto shows EP241 (not EP341)for my 91 TPI 305.

Bob88GTA

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Yeah, gonna check all that out. Car sat for so long before I bought it, who knows whats stuck or what. Other than yesterdays ordeal, it runs fantastic.

greenyone

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I need glasses.

thtanner

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You reply wayyyy too quickly. I edited that in like .05 seconds after posting.

greenyone

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my internet connection has a new fuel pump

RBob

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That is good, your CCP and tank venting is working correctly. As for the FSM, here is the CCP/venting diagram from the '92 FSM. Note that it was drawn/written in April of 1991 for the '92 MY. This is why last minute changes don't get into the manual. FYI, the '92 MY also uses a solid non-vented gas cap.

RBob.

RBob

iTrader: (1)

Which engine? I may be able to get some information on that setup. I did look through some for the '85 MY w/4-bbl and with TPI. Complicated systems. This is part of the issue when discussing the CCP and tank venting systems. They range from utterly simple such as greenyone's '91, to MYs such as yours ('85).

Want a system that is overly complicated, take a look at some of the crossfire engines.

RBob.

Bob88GTA

iTrader: (2)

Bob
It is the 5.0 TPI Engine 57k miles, but sat for like 12ish years. Been running great for the last year plus, no problems. But MAN WAS IT HOT HERE YESTERDAY! I don't normally drive it to work, mostly up the road a couple miles every week or so. So I noticed this just yesterday.

greenyone

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HA. Maybe I should have bought the 92 manual.

RBob

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Wow, they carried through the diagram from the '89 MY. Other then the tank venting it is close.

RBob.

greenyone

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Is that diagram even accurate to an 89? I thought the general consensus was that thirdgens all have non-vented caps and use the remote tank vent?

RBob

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OK, tough system to get good information on this as it was a change-over year that included both carb's and TPI. I attached the vacuum diagram information for an '85 Firebird TPI. See if that matches your setup. Also, here is a link to the '86 CCP system description and troubleshooting. Appears to be the same as the '85 system:

https://www.thirdgen.org/forums/tech...-solenoid.html

RBob.

Bob88GTA

iTrader: (2)

RBob
Thanks, thats the same sticker under my hood. I will check the testing link out!

greenyone

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This may seem like a hack fix. But since everything I can test on the EVAP system checks out/passes with flying colors and dropping my tank to inspect/replace the pump/sender/pulsator seems silly since the pump keeps perfect pressure and the car runs great otherwise...I drilled a couple very tiny holes through the gas cap to keep the pressure from building up so high in the tank. I'm going to switch back to the regular non-vented cap once the weather cools off and see if the problem still happens when it's not 97 degrees outside.

Bob88GTA

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I'm gonna check out my system this weekend. I'm sure the canister and vent valve needs replaced/serviced after 31 years!
Good luck greenyone

greenyone

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I'm sure my ancient canister needs replaced too. But since you can blow air into it with little to no effort I'm not gonna drop the 100 to 200 bucks on a new canister just yet. I also blew some compressed air into the hose that leads to the remote tank vent in the driver wheel well just to see if it was obstructed. With the cap off air just comes right out the filler neck. With the cap on it blows freely all the way up to through the canister. It's infuriating. It seems like such a simplistic system with very few parts.

Bob88GTA

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I don't want to drop that kinda money either, but I need to do the checks like you did first and get a starting point.

As mention SO MANY TIMES in other threads, I'm also going to fill it up with Pure Gasoline with no Ethanol and start my test with that.

RBob

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There are some years that 3rd gens had vented caps. Not sure if GM folks were still figuring out evaporative emissions or if the EPA was requesting an ever changing spec.

RBob.

RBob

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I'm not sure why you are beating a dead horse. As I've mentioned several time in this thread, your evaporative emissions control system is working correctly.

If the whining at the vapor pressure control valve bothers you, try a new valve.

RBob.

greenyone

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If you can send me a couple hundred gallons of that...that would be great. I'm starting to seriously think this ethanol laden fuel is a major cause of the problem. I had an 88 Iroc back in the early 1990's and lived in Oklahoma where it was 90 all day long in the summer months. I never had this issue. Fast forward to 2016 and the problem occurs pretty much only when it's really hot outside here in Western Pennsylvania. Maybe that water absorbing ethanol just expands under heat faster than the evap system can handle. I think for now maybe I'll try dumping a bottle of dry-gas in with every fill.

Bob88GTA

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Pure gasoline here is 2.55 a gallon, so it's not too bad

greenyone

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Can't find strait gas here in PA anymore. Darn ethanol mixed gas just mucks up everything. My older carburated boat hated it. My lawn equipment is not happy either.

Bob88GTA

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UPDATE!
I took apart my tank vent valve. It was stuck closed. It took about 30lbs of air to open it. Cleaned it all up and reassembled. It opens around 5-7 psi. So much better now. Also changed out the vacuum hoses at the caninster and plenum. They weren't rotted, but were deteriorating causing that black powdery crap.
We'll see how it goes from here. The valve was the big thing so far.