This is a funny question, but when I put the IROC in park and slowly rev the engine it is smooth all the way to about 1700-1800RPM and in that area it feels like it is missing badly and sounds really raspy and harsh (for lack of a better word) under the hood. Rev it on past that and it's fine up to 4000+ RPM, it just acts that way at this one specific engine speed. Which happens to suck because it's in the RPM range I cruise at on local highways. It sounds like a bad harmonic in the exhaust system (stock with Dynomax catback) under the hood or something. No broken valve springs since it did it before and after I replaced them, so what could cause it to act this way at one specific engine speed? The cam or something (stock)? Burnt valve? Plugged cat? Exhaust leak? Also, overall it doesn't seem to be nearly as powerful as it should be, as in it won't chirp the tires unless I'm being a real jackass. Thanks guys, I'm at a complete loss on this one since I've done almost everything to it by now.

------------------
1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, Accel coil, 180 t-stat, Bald Eagle tires,
Hypertech fan switch, Accel 23# injectors, Holley AFPR, ported plenum,
Ruger P95DC, hot wife, new oil filter, thick rubber floormats.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."

 

Just a guess because cars like to detonate under load at that rpm... whats your fuel pressure set at? I see you have 23# injectors, and I hear the SD cars are rich as it is. I think you need to get the fuel pressure down to where the #'s are 21.5, and of course if you have already done that I have no idea

 

Thanks, madmax. I've got it set at about 41psi without vacuum applied but the car was doing it before I replaced the fuel injectors so I ruled it out. I monitored the car in field service mode and it is going into closed loop and seems to enrichen the mixture more often than it leans it, so I'm at a loss on this one. Thanks for the response.

 

How about looking for a lightshow under the hood tonight? Usually a miss occurs everywhere with bad spark, but who knows...

Besides, someone else needs to throw in an idea here...