1991 L98 Revving/Bogging Problems
Thread Starter
5th Gear
Joined: Apr 2011
Posts: 5
Likes: 0
1991 L98 Revving/Bogging Problems
I have a 1991 L98 Auto that was driving down the highway, suddenly lost all power and died..
T
I had it towed home and started it up, it idles fine but if you try and rev it, it sounds like it has retarded timing or running out of fuel.
I have checked the fuel pressure, left the gauge hooked up and ran the car...no fuel pressure issues. I was sure this was gonna be the problem
I hooked a timing light up to it, and the timing appears to be right on.. I'm very confused. I checked all the plugs they don't appear to be fouled.
There is no codes in the computer what so ever. I can start the car and it will idle perfect for an hour, no misses, perfect. I can slowly rev the engine and it will climb, if I try and rev it quickly it just dies.
I checked the TPS voltage, replaced the ait sensor..really kinda stumped, any ideas would be appeciated. Oh I also took the cap off and everything looked new..
Thanks for any input!
T
I had it towed home and started it up, it idles fine but if you try and rev it, it sounds like it has retarded timing or running out of fuel.
I have checked the fuel pressure, left the gauge hooked up and ran the car...no fuel pressure issues. I was sure this was gonna be the problem
I hooked a timing light up to it, and the timing appears to be right on.. I'm very confused. I checked all the plugs they don't appear to be fouled.
There is no codes in the computer what so ever. I can start the car and it will idle perfect for an hour, no misses, perfect. I can slowly rev the engine and it will climb, if I try and rev it quickly it just dies.
I checked the TPS voltage, replaced the ait sensor..really kinda stumped, any ideas would be appeciated. Oh I also took the cap off and everything looked new..
Thanks for any input!
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
It will run the way you have described if the exhaust system is plugging up.
Quick check with stock exhaust: Drop the head pipes from the manifolds, about 1/2 inch on each side & start the engine. If the exhaust system is bad the engine should now respond normally except for the noise.
If the problem is still there you have eliminated the exhaust as a possible problem area.
Quick check with stock exhaust: Drop the head pipes from the manifolds, about 1/2 inch on each side & start the engine. If the exhaust system is bad the engine should now respond normally except for the noise.
If the problem is still there you have eliminated the exhaust as a possible problem area.
Last edited by Churchkey; Apr 1, 2011 at 09:22 PM.
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
Just a few suggestions.
Try it with the intake duct off the throttle body.
Check the voltage on the distributor feed wire while running & reving.
Other than previous mentioned items a weak coil or an ignition module could cause similar problems.
Try it with the intake duct off the throttle body.
Check the voltage on the distributor feed wire while running & reving.
Other than previous mentioned items a weak coil or an ignition module could cause similar problems.
Thread Starter
5th Gear
Joined: Apr 2011
Posts: 5
Likes: 0
Thanks for info, I didnt even think about the ignition module since it idled so well, but yeah flakey electronics can do weird things. I will give that a shot! thanks! Also I unplugged the TPS and it doesnt make a differance what so ever, I guess with it running so poorly maybe that doesn't mean anything. I've checked the 0-5v at the tps.. it's correct. I'll try the ignition coil and if that doesn't work I guess I will try making for the tps feedback is getting there..
Thanks!
Thanks!
Thread Starter
5th Gear
Joined: Apr 2011
Posts: 5
Likes: 0
Well I have now:
Dropped the exhaust
Checked the TPS
Replaced the AIT sensor
Replaced ICM
Replaced Coil
Checked Fuel Pressure
Checked Injector Ohms
I guess at this point, I'm looking for the rat that chewed a wire
somewhere?
Dropped the exhaust
Checked the TPS
Replaced the AIT sensor
Replaced ICM
Replaced Coil
Checked Fuel Pressure
Checked Injector Ohms
I guess at this point, I'm looking for the rat that chewed a wire
somewhere?
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Instructor
Joined: Jun 2008
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From: Norman OK
Was there a voltage drop as the engine came up to operating temps?
When I first got my 91, the "pink" bat feed wire insulation was brittle where is passes behind the left valve cover/head. Had several of the same symptons you describe.. I spliced in a new longer section and all was well until I later trapped it under the valve cover, but that's another story.
To chase the wire, it runs from the ign terminal of the coil to G1 of the bulkhead Connector C100. Then from the bulkhead connector to C2 on the ignition switch. It is pink all the way and there is a splice between the bulkhead connector and the ign switch to feed the ccm, injectors, air bag, gauges, etc in the main fuse block.
Also, take a look at the 4 wire flat connector (C1) at the rear of the dist. That bundle carries ref hi & lo signal from the ign module to the ecm. That wiring also runs to the est bypass connector. The flat connector is normally buried behind the oil psi sending units.
FSM 8A-20-5
Last edited by OkieC4; Apr 4, 2011 at 12:22 AM. Reason: add fsm ref.
Cruising
Joined: Apr 2010
Posts: 12
Likes: 0
Sorry had to bring this old thread back. I am having the same problems as the poster & have replaced the ign mod, fuel pump, filter, pressure at 50psi, new plugs wires cap. Timing is on & injectors were sent to be cleaned. No codes here so im lost on this one. The car runs pig rich & misfires as you rev it. I have been chasing this problem down for a year now. Any advise would be great!
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