The adjustable fuel pressure regulator on my '89 has ,shall we say "Passed Gas??".

I found better than a cup of raw gas in the plenum, yesterday.

I glad the garage didn't blow up. The stench was overpowering.

Nothing like a panic repair at 7:00PM.

This is the second one of these things to go south on me in two years?

The first was a Famous Name Brand, the second was generic from a Large Supplier.

The question is: " Is there a mfg/model that won't do this???"

TJM

 

Glad you caught the problem. For what it is worth - I got a super inexpensive FPR diaphram from "thepartslady" on flEaBay a couple of years ago....part still works to this day (knock on wood).

 

It appears that it is NOT the fuel pressure regulator?

I find evidence of at least a full cup of raw gas in the plenum.

It puddle up filling the heat riser chamber beneath the plenum, until that was flooded and then into the Throttle body, MAF, and into to flex connection to the air filter, and into that as well!!!

The Plenum is dust dry between the vacuum connection of the Fuel pressure regulator and the throttle body. If that much gas ran down the plenum I would see a path. No path.

So that leaves the tank Evap system?

Now for the other peculiar thing. The car will stall out with the gas cap off?? Happened during the emission test a couple months ago and I have driven very little since then. It acted like a vacuum leak?

So I am guessing this gas has to be from the Evap system?

But HOW does that much gas get to the Plenum through all the tubing and solenoids and the canister [ up hill too!] ?!!??!


I don’t know what the PPM for ignition in a two car garage volume is but I’ll bet I was close?

TJM

 

I think you should move the car outside and leave the gas cap loose till one of these folks posts a vac diagram. Seems like the tank is pressurized? GOOD LUCK!

 

Vacuum
If the solenoid was constantly allowing vacuum to canister, there is a chance that fuel splashing around tank, could get sucked up by the EVAP fitting, at top of tank.
The fact that you say, removing the cap will stall it out, seems to confirm this.

http://members.shaw.ca/corvette86/Ev...l%20System.pdf

 

Yeah, I have concluded that the likely culprit is a bad diaphragm in the Tank Pressure Control solenoid. It is located in the left front section near the EVAP canister.

The circuit indicated in the FSM shows that this could happen.

It is ironic that a plastic car would have plastic EMISSIONS part that if it fails, would allow the EPA mandated pressurized tank to force gasoline into the air [ through a tiny 1/8" dia. line] , and possibly set the PLASTIC car on fire [ and burn down my house in the bargain?]

Wouldn't this create more crap in one fire than all the gas vapor in the life of 20 cars?


TJM

 

The tank is pressurized . It's an EPA sort of thing.

Agent 86 was kind enough to pop a diagram up there, but it's an 86 diagram I think. A little different than the '89.

This is something folks should look at though, it seems a fatal flaw and something easily missed. The car ran fine, no codes because it's a vacuum operated device. The thing that clicked this am was the stalling with the cap off. A vacuum leak no doubt. I just didn't put it together until now.


[ At least I am pretty sure the Tank Pressure Control is the culprit?].

Still hoping for confirmation from someone.

TJM

 

No one tuned in that has had this happen Huh?

Well, I guess I'll buy the new parts going on my theory.

TJM

 

Yes it's 86 info. Not sure what's different, other than vacuum sources, but it may help with testing.

 

Bump

 

The '89 has a Tank Pressure Control Valve.

It is in line with the from the tank itself, then travels to the canister.

It is operated through a small vacuum line, whose port is at the throttle body.

When running, and vacuum is applied, and the valve goes "Full" open and allows vapor to flow freely to the canister.

When "OFF" the valve closes and vapor is vented [ via the same path ] only through a restricted opening that greatly limits vapor travel, until pressure builds in the tank... like a big temperature change .. then [ in theory] the vapor goes to the cannister.

Now if the diaphragm goes bad, the the pressure builds and appears to send the vapor to the throttle body, where it condenses into liquid.

I can see no other way what happened could happen.

Must be rare for no one at all on the forum to have ever had such a problem.

GEN III reports identical [ and frequent ] such problems.

Thank you Camaro Lover's.

TJM

 

My experience is most aged fuel tank vent tubes crack or rot off so the fuel/vapor never gets to the canister. FSM probably just says to replace the canister...post what you fix works out to be.

 

Will do.

C.C. sending the parts.

TJM

 

What if the tank is full (and/or the vapor pickup is able to pick up gasoline vs vapor), could expanding fuel get squeezed into the TB?

I (and at least another member) have found out what happens when you disconnect fuel lines and let the car's butt get exposed to the sun. Heat causes fumes/gas to expand in the gas tank -- which will push fuel out of the lines that connect to the fuel rail. We've ended up with raw gas on the intake (and a garage nearing explosive condition! My garage ain't that far away from the ignitor on my furnace!!!! )

I'm trying to think of another way fuel could get from the rail to the TB. For example, the FR is controlled by a vacuum line. Is there a path thru the FR to the TB? (Mine is disassembled right now! LOL)

gp

Oh yeah...if the vapor pickup (for the vapor control system) was built correctly, how could liquid vs gas get into that line? IOW, what prevents gasoline from making it to the vapor cannister? If you can't explain that, you have to look for an alternate scenario, right?

 

The system was built "correctly" just with a fatal flaw, I am thinking. [ I like the '86 method, but not as "green" I am sure].

The liquid gas I found was the condensation of the tank vapor. [Think Uncle Billy's Moon Shine still!!!! ]. The evaporation is natural as it is a pressurized tank system by design, and vapors [ and pressure to push those vapors] are a normal conseqeunce.

The '86 diagram shows where it goes... to the canister then the thing is "purged" when running. Not so with the '89 it has this stinkin' Control Valve.

So when the Valve fails, there is no other route, the liquid condenses out at the cold TB...... Voila!!! Liquid gas build up.

No odor until it tops the Plenum inlets [ 1/2 cup] and pours into my MAF [ which is also probably screwed] ........ and into the air filter.

Yes, Dorthy!!! into the air filter...!

Not so when working correctly because it passes through the working valve and to the charcoal canister, where "most of it" it is supposed to go. The ECO god then purges the canister when running [ IF another ECM controlled valve works!!!].

So....... and since I have had no one with a duplicate experience, I will hazard a guess sit is a highly unusual event. Only one GEN III guy has had it happen.

OR....??? It just isn't noticed a lot because of driving the things will take a smaller amount of the fuel out of the Plenum and just run a tad rich for a bit......... or???....... The big fire destroying evidence and we blame the Fuel Pressure Regulator???

More than one burned up 'vette picture has passed this way!?!?!?!

TJM

PS: I think that Akhmed puppet designed this ..."I'll kieeel you!!"