vacuum or ignition problem
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Joined: Jan 2006
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From: Pittsburgh
Car: 1987 firebird
Engine: 1995 lt1 383
Transmission: 4l60e
Axle/Gears: moser 9" with 3.70
vacuum or ignition problem
Car: 1987 firebird with a 12.5:1 compression 1995 lt1 and 4l60e
Ok my problem is that the car seems to be missing at idle. The car starts and idles fine, maybe a little bit rough. When I drive the car it has a slight stumble right off idle and when come to a stop the idle will surge and the car wants to stall out, but after surging for a couple of seconds the idle smooths out.
The car has a brand new MSD optispark, ICM, VSS, and plugs since my rebuild over the winter. I strocked the lt1 to a fully forged 12.5:1 compression 383 with direct port nitrous. I also sent the computer back to pcmforless to reconfigure for my current set up since this build up.
I pulled the plugs and they all look good (tan) and leak tested all the vacuum parts with carb and choke cleaner and map gas. I found no obvious vacuum leaks but running on vp racing fuel when I sprayed map gas and carbon choke cleaner on an open vacuum line I pulled it had very very little effect??
I also put a vacuum gage on and it hold 14-15" of Hg. The thing that is confussing me is if I pull a vacuum line off the gage vacuum does not change, but when I pulled all the nitrous lines off the intake it dropped to 11 or so.
I am also getting no codes and the sensor values seem to be correct? So do I pull the whole intake off and start at the intake seals an reseal everything up? Or do you think that it is in the ignition?
Ok my problem is that the car seems to be missing at idle. The car starts and idles fine, maybe a little bit rough. When I drive the car it has a slight stumble right off idle and when come to a stop the idle will surge and the car wants to stall out, but after surging for a couple of seconds the idle smooths out.
The car has a brand new MSD optispark, ICM, VSS, and plugs since my rebuild over the winter. I strocked the lt1 to a fully forged 12.5:1 compression 383 with direct port nitrous. I also sent the computer back to pcmforless to reconfigure for my current set up since this build up.
I pulled the plugs and they all look good (tan) and leak tested all the vacuum parts with carb and choke cleaner and map gas. I found no obvious vacuum leaks but running on vp racing fuel when I sprayed map gas and carbon choke cleaner on an open vacuum line I pulled it had very very little effect??
I also put a vacuum gage on and it hold 14-15" of Hg. The thing that is confussing me is if I pull a vacuum line off the gage vacuum does not change, but when I pulled all the nitrous lines off the intake it dropped to 11 or so.
I am also getting no codes and the sensor values seem to be correct? So do I pull the whole intake off and start at the intake seals an reseal everything up? Or do you think that it is in the ignition?
Thread Starter
Member
iTrader: (5)
Joined: Jan 2006
Posts: 366
Likes: 0
From: Pittsburgh
Car: 1987 firebird
Engine: 1995 lt1 383
Transmission: 4l60e
Axle/Gears: moser 9" with 3.70
Re: vacuum or ignition problem
The vacuum line was for the fuel pressure regulator, and I think that it is too small to register on the vacuum gage.
Anyway I still have the problem and do not know where to look.
The plugs all look good, so does that mean that it is not in the ignition? I also tryed to compression check the cylinders but only could get to three with out dropping the exhaust and moving the headers out of the way, but those three were consistent.
I am about to pull the intake and put new gaskets and reseal everything, to ensure there is no vacuum leaks, but I am unsure.
Could it be a seeping head gasket? One cylinder leaking into another. Could that cause this problem?
Could it be the computer tune?
I am at a lose with this problem, do you guys have any ideas?
Anyway I still have the problem and do not know where to look.
The plugs all look good, so does that mean that it is not in the ignition? I also tryed to compression check the cylinders but only could get to three with out dropping the exhaust and moving the headers out of the way, but those three were consistent.
I am about to pull the intake and put new gaskets and reseal everything, to ensure there is no vacuum leaks, but I am unsure.
Could it be a seeping head gasket? One cylinder leaking into another. Could that cause this problem?
Could it be the computer tune?
I am at a lose with this problem, do you guys have any ideas?
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