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91 L98
Automatic 700R4 with B&M shift kit added 2 years ago when rebuilt
Ok here's the story, I autocross my car and recently I've had this intermittent issue where it seemed like the car was down on power. It didn't pull or rev up as fast as it normally does. Sometimes I would make a run and it would be fine, then the next run it would seem like it was down on power. I was thinking it was some sort of fuel issue so I borrowed my dad's pressure gauge. Let's just say it was fine while driving, even during a leak down test it held more than 20psi overnight. However, when I took it out on a test drive with the pressure gauge hooked up, the car started to shift weird. The car would go through one gear and then hold rpm for a few seconds just before it should shift and then it would shift very hard. Going through 2nd gear it would do the same thing. It almost seems to be getting worse now. I've checked fluid level and it is good and still translucent red, no burnt smell. I just checked codes in the computer and there are none stored. At this point I am assuming I have some sort of transmission pressure issue causing all of this and need to take it back to the place that did the rebuild. Any other ideas?
If it still has cats I would check to be sure they aren't restricted. I would also make sure fuel pump baffle hasn't come loose if cat isn't restricted.
If it still has cats I would check to be sure they aren't restricted. I would also make sure fuel pump baffle hasn't come loose if cat isn't restricted.
I had thought of cats but don't really have a way to check them at this point. I pulled the fuel pump and everything in there looks brand new. The strainer still seems sturdy enough to not collapse. I've owned car for 3 years and I never did anything with pump. I know the previous two owners but haven't asked them if/when pump was replaced.
How about your Knock sensors? I had one fail and it sure makes the L98 seem anemicwithout the extra timing.
Common misconception is Knock sensors only hear knocking noises from down deep. In reality they can hear "lot of noises" that could make them "retard" your ignition. When they detect a noise they send a signal to your ECM and it pulls back the timing on all 8 on my 1988 L98. On the newer Corvettes it only pulls the offending cylinders timing and returns it quickly unless it hears more knocking.
The easiest way to test your Knock sensor is to take a small metal wrench or ratchet and tap on the cylinder heads. If you tap loud enough the knock sensor should pull timing and your idle will change a bit.
I don't know much about modern transmissions but don't they use a vacuum signal for shifting as well or is it only the TV cable now? A weaker vacuum signal might have something to do with the way it is acting....maybe?
Good Luck!
If the intake screen for the fuel pump is out of the gasoline would that be an issue. I would switch the pump strainer for a piece of Holley's new Hydra-mat. That stuff is amazing and it really works. I have a section of it in my C3.
Last edited by ctmccloskey; Aug 6, 2021 at 09:49 AM.
So I think I found my issue. Dropped exhaust to find pieces in my cat. Probably pieces from the pre-cats that ended up in the main cat. Going to have to replace all of them at this point. Looking for parts if anybody has them.
Time to update Rule 2.7.1.12.2 Catalytic converter and Pre-converter Except - may be removed/bypassed only on 1982-older
If the cost is outrageous there may be precedent.
I would at least like it to allow to update to a newer more efficient converter that eliminates the pre cats. Right now, I'm looking at about $1000 to replace the y-pipe with cats and the main cat. Half that if I could eliminate the pre-cats.
I preemptively support your gutting the pre-cats for the time being. We should not be concerned with forcing OE catalyst replacements on a 30 year old car, when the cost for replacement is likely a significant percentage of the car's value. It's allowed on older cars, time to update, through 91 in my opinion.
Gut the pre-cats, put a new main in and put it back together for this weekend.
Last edited by 69autoXr; Aug 31, 2021 at 10:19 AM.
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Low power and weird shifting issue
