1989 L98 lacks power
Thread Starter
Intermediate
Joined: Aug 2023
Posts: 38
Likes: 5
1989 L98 lacks power
Recently purchased 89 convertible with I'm guessing about 100k on the motor. Car idles steady at 6-700 at idle, but is just a bit rough. Not enough to be a straight miss, but not smooth. When driving, a quick stomp on the gas pedal sees the tach go from about 1200 cruising revs to 3000 rpm quickly, but it doesn't get any higher on the rev range. Between previous owner and I, lots of new stuff including injectors, FPR, fuel pump assembly, cap, rotor and wires. Thought it might be a clogged exhaust so dropped and found front two converters semi-plugged. Center cat had been gutted sometime in the past. Installed new front straight y-pipe which helped a bit. Car acts like timing isnt advancing, but that's just a guess from someone used to old style GM small blocks. This must be the first in a long line of SBChevys I've owned that doesn't puff any smoke at either start up or WOT, so I'm thinking the basic guts of the engine are still decent, but I have my doubts about the cam and lifters. A quick compression test showed a bit down on compression (120-130 each). but nothing that would identify a weak cylinder. I'm running out of ideas and open to any help available. Thanks in advance!
Thread Starter
Intermediate
Joined: Aug 2023
Posts: 38
Likes: 5
Everything seems to work as designed at the throttle body. TPS reads where it should at closed and wide open, and IAC recently replaced as well. I cleaned and regasketed everything at the TB when I had everything apart to change the injectors. Thanks for the reply.
Melting Slicks
Joined: Jul 2005
Posts: 2,221
Likes: 302
Are you sure the factory memcal is in the ECM? Maybe someone played around with it.
Also check the ignition module and make sure its a factory GM. Aftermarket ones can actually alter the timing delivered to the engine despite what the ECM is commanding.
Also check the ignition module and make sure its a factory GM. Aftermarket ones can actually alter the timing delivered to the engine despite what the ECM is commanding.
Thread Starter
Intermediate
Joined: Aug 2023
Posts: 38
Likes: 5
Opening the ecm is not something I had thought about. I’ll give that a try. I did look at the ignition module and saw no numbers or ID on it at all. Guess I’ll dive in there as well. Are GM replacements still out there?
Melting Slicks
Joined: Jul 2005
Posts: 2,221
Likes: 302
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