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Thread: The strangest demon ever....
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11-26-2004 #1
The strangest demon ever....
Okay, I need everyone's thoughts on this...I mean even the people who normally don't post as anyone's experience would be helpful. Myself, along with some very experienced people are having an issue with a car we cannot figure out. To start, it's an 88 camaro IROC-Z that was bought less motor/trans to be a fun car to test stuff on and to beat up a little in the process for the sake of numbers. Currently the motor is slightly worked 355 backed by a TH350 and run to some 4.10s. The issue we're having is with the fuel system. Because it's a retrofit carbed application, the pickup in the stock tank was modified and then checked twice for clearance in it's appropriate baffle and we capped all lines going into the tank (total of 4) except the vapor return line, which we attached a breather to, and of course the main feed line. Main feed drops approx. 14" down to a filter, then holley blue, then aluminumn line approx 6', another filter before the regulator set at 8psi, then to the Edelbrock 750. With the exception of the fuel tank line and the aluminumn line and it's connections, everything is stainless braided and uses -6an. The problem we're having is after the car has been running for about 1/2 hour, regardless of how we treat it, we start loosing fuel pressure slowly but surely. Doesn't matter if it's WOT or idling, we loose it at about a PSI every ten minutes, the only constant being the car running. If we shut the car down and then restart, it just picks up where it last left off. If the car cools down completely, it's starts right at 8PSI and stay's there until about a half hour again. The car has been through three fuel pumps, two regulators and a completely re-done fuel system including a different carb and the same problem no matter what. We checked voltage to the pump at the pump and it doesn't change and we upped the car to a 90Amp alt just to be certain. It just doesn't make sense because it's not temp related...we could cook it as soon as it fires up and the temp could be holding at 160 and then pump won't crap out until about the 1/2 hour mark. The only way we know is the A/F gauge starts going hot and sure enough we've dropped down to 5 or 4 PSI.
I'm sorry this is long but wanted to give you guys everything to scratch your heads over. Everything in the fuel system has been replaced which would indicate that it's not the fuel system but we're all miffed over here. Any suggestions....questions? Thanks guys...
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11-26-2004 #2New to Pro-Touring- Join Date
- Aug 2004
- Location
- bremerton, wa :(
- Posts
- 7
And you are positive it has adequite venting in the fuel tank?
11-26-2004 #3Banned- Join Date
- Aug 2003
- Location
- Orlando, FL
- Posts
- 8,745
Interesting
We have a 1984 project car doing somehting real similar, it is also a carburated pee wee. It is running out of gas (fuel pressure) out of the blue. Then will pick up pressure for no reason.
We have not spent anytime checking out the problem yet, but I am fairly cetain is is cavating some how, or sucking air. I will be looking to the rubber lines that conect from the regualtor / pick up to the body line? Or the pick up line in the reuglator inside. I had a pick up line that developed a hair line crack on the inside, against the regulator retaining ring. It drove me frickin nuts trying to chase a "vapor lock".
I'll be watching to see what you find. We probably will not mess with this one for a couple weeks. I will let you know what we find.
11-26-2004 #4Does the line run close to the exhaust or any other hot parts? It could be boiling the fuel in the line maybe?
11-26-2004 #5Hmm...I wonder-try using only one filter. Run it just before the carb under the hood and see what that does. -Jabin
11-26-2004 #6I doubt it's vapor lock...that doesn't go away that quickly normally.
My bet is 1) the stock injection pickup sucks for a carburetor pump, or 2) the tank isn't vented good enough and you're pulling a vacuum in it. #2 being where my money's at.-Matt
Welders: The only people that think a co-worker catching on fire is funny.
11-26-2004 #7Have you tried running it without the tank filler cap on? Cheap way to see if it's a venting problem(which is what it sounds like).
Brian D
Snotty Bimmer driver.
11-26-2004 #8We've run this combo before with only one filter and now both filters are the very nice Earl's replaceable element style using the -6an's. The only heat the line is exposed to is a very brief encounter with one of the tranny lines (for about 1" and it's not quite touching) Now, the pickup was originally for an in-tank pump w/ screen on a TPI setup. The diameter is 3/8 so we measured where the stock pickup ended in the tank (and where) and matched that length and location with aluminumn line. The hairline crack is a possibility and I didn't think to pop the gas cap off to check. I'll let you guys know...definitely. I've never encountered a problem like this before. Thanks again you guys.
11-26-2004 #9Vacuuuuum!
I agree with Brian D in the gas cap issue. The one thing I keep wondering about is: Did the car work fine with the original engine?
If it did, can this maybe have something to do with the fact that the return line was used then but not now?
Torbjorn
11-26-2004 #10Originally Posted by Torbjorn
11-26-2004 #11Return line
Dont think you actually need one, but maybee it helps preventing vacuum in the tank if the vent dont work well.
It may also be an advantage with a return line if you have problems with boiling fuel. The sirculation prevents this
Torbjorn
11-26-2004 #12