L98 Probs! - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 8 (permalink) Old Dec 31st, 00, 06:01 AM Thread Starter
 
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Hello all..

I recently purchased a 70' with a 87 L98 engine installed. The guy I bought it from had just finished the installation of the engine when I bought it. The motor appeared to run fine with no problems.

A few days later the motor started surging a bit at low rmps especially leaving from a stop sign. It wasnt bad, and I could accelerate through it. My thought was the injectors were prob. a bit dirty so I went to the autoparts store and picked up a bottle of Chevron fuel injector cleaner. I drove the car around for about 45 minutes with no problems. Later that night I took the family out to dinner in the malibu (the restraunt was about an hour away) and just when I pulled in to the place the car died! I waited about a minute and restarted the car, it started ok but then seemed to loose fuel pressure. When I stepped on the gas the car would just stumble and not accelerate.

Ok.. I figured that the cleaner just got a bunch of gunk loose and cloged the fuel filter.. no biggie.. After eating dinner the car started up and made it home (barely) but then died 1 block from the house. We walked home and I went and got the car an hour later. So yesterday I changed the fuel filter, the old one was full of junk. I figured Id solved my problem. After changing the filter I let the car idle for about 90 minutes out in the driveway and low and behold the same problem. The car seems like it loosing fuel pressure. You can tell its starting by the surging, it seems starved for fuel and then seems to get a bit more fuel, the rpms jump up a bit. When I try to give it a little gas sometime I can pull it out of its 'starvation' and get the engine stable again, but eventually it will die. The car will not restart imediatly after this happens but if I let it sit for 5 mins or so it will restart and the problem usually reoccurs after 10 mins or so.

So, Im not sure what the problem is.. there appears to be 3 issues that I can identify:

1. The injector cleaner is screwing something up somehow. Could the filter be cloged again?

2. Something wrong with the fuel pump that causes it to die after 90 mins or so of operation even though I can hear it running.

3. Heat, perhaps the gas is perculating (sp)? Ive driven the car longer in traffic for 2 hours before with no problem.


So Im not sure whats going on.. Id hate to drive the car to the local chevy dealership and pay 100$/hr to have them diagnose the prob..

Anyone have any suggestions at all?

THANKS!!!!
Joe
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post #2 of 8 (permalink) Old Dec 31st, 00, 10:23 AM Thread Starter
 
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Ok, heres whats happening.. At idle the pressure is at 20-25 psi, after about an hour or so of idling the fuel pressure drops to about 10 psi and the motor dies..

After trying to restart the car the pressure is still at 10 psi and the car will only run for about 10 seconds before dieing..

I did not hear the fuel pump when the pressure dropped but when trying to restart I could hear it pumping, but with no increase in pressure..

Soo.. my assumption is that theres something wrong with the fuel pump.. in that after an hour or so of working it just poops out..

anyone agree or disagree?

Thanks guys!
Joe
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post #3 of 8 (permalink) Old Dec 31st, 00, 11:34 AM
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Jody
 
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Pump and/or pressure regulator. A clogged filter would do this also, but you replaced that I believe.

That engine should have 40-43 psi of fuel pressure at idle. Unfortunately the regulator or pump could cause this problem. I'd lean towards the pump since the pressure drops the longer it runs. I don't think the regulator would do that.

Jody
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post #4 of 8 (permalink) Old Jan 2nd, 01, 10:26 AM Thread Starter
 
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ACK!!

Ok, I just changed the fuel pump and everything looked ok at first..

Then the same thing started happening again! as soon as the motor got warmed up the pressure dropped to about 15 psi and the motor died..

I wanted to check the electrical connections just to make sure so I ran a lead directly from the battery to the pump with no change, same problem.

Is it safe to assume that its the pressure regulator? Id hate to have to rip off the manifold to replace it..

Thanks!!!
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post #5 of 8 (permalink) Old Jan 2nd, 01, 10:47 AM
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Mark
 
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Is it a new gas tank? If it's a 30 year old tank, it may be full of rust. What kind of junk was clogging up the fuel filter?

Mark
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post #6 of 8 (permalink) Old Jan 2nd, 01, 11:19 AM Thread Starter
 
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Ok.. after alot of yelling and cussing.. I jacked the car back up and blocked off the return fuel line.. pressure shot up to about 70 psi in about 10 seconds.. I shut off the motor because im not sure how high a pressure the motor can take (I dont want to cause anymore probs). Soooo my assumtion based on this test is that the pressure regulator is bad?

Whatcha all think?

Thanks!

PS.. anyone know a good site that walks you through the replacement of the pressure regulator?
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post #7 of 8 (permalink) Old Jan 4th, 01, 04:34 PM
 
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The L98 is a tuned port injection motor. It is supposed to have about 70 to 75 psi fuel pressure. As for the other stuff, Im thinking that your sensors might be going bad. I have a friend that just replaced three fouled sensors in his Bronco causing near the same problems your have. He had the mass-air, exhaust gas temp, and oxygen sensors replaced. Im hoping this might help you.
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post #8 of 8 (permalink) Old Jan 4th, 01, 05:49 PM
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Jody
 
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Sounds like the regulator. It is not supposed to have 70 lbs of fuel pressure; more like 40-43 at idle. But since it gives you 70 when the return is blocked off I would think the pump is fine and the regulator is faulty.

Jody
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