well as the title says, I'm havin some trouble with my 94 z28 6speed. my uncle swapped in an lt1 from a corvette with about 70k miles on it. lately the car idles perfect, but when I get on it, it hesitates, then seems to be ok at mid rpm range but almost seems to cut out power a little at around 4500 rpm. there was some junk in the filter at one point but we cleaned it out replaced and ran through some cleaner for everything. also checked the fuel pressure and that seems to be fine. the plugs and wires are also new. It also seems like it might need a starter as well. someone told me they thought it could be the computer. I havnt checked for codes yet, havent had time. any input would be appreciated, thanks.

 

Does it still have a working EGR?

 

from what he's told me, yeah. (it's at his house at the moment) but definetly something ill look into.

 

anyone else have any ideas?

 

It could be all kinds of things with an engine that old. I would check all the usuall things first.

Check for vacuum leaks especially around the intake manifold - check the bolts to make sure they are tight. Check all the vacuum hoses and any of the hoses going to/from the throttle body, valve covers, and intake manifold for cracks. Check the intake elbow to make sure there aren't any tears in it, especially underneath. Get some spray cleaner and clean the MAF sensor carefully. With the EGR, you want to check it for a ruptured diaphragm and plugged up passageways in the intake manifold and EGR valve. The distributors in those year of cars were troublesome and could cause similar symptoms. They are kind of hard to troubleshoot and expensive and a pain to replace, but keep it in mind if you think it's ignition related. As far as the fuel pressure, did you test it just at idle or did yout ape a gauge to the windshield and test it under throttle where it is losing power at 4500 rpm. Does it do this in every gear or does the rpm change depending on what gear you are in (IE: is it worse in 4th than 3rd?)

 

I changed my plug wires and shortly after I had one burn on the exhaust manifold. It would run, but got worse each day until I found it. I think you can check it easily in a very dark place with the engine running. Of course like others said, there are truly 100's of possibilites. I just had my air intake come loose once and it caused all sorts of problem. I assume the car ran very good for a while, before this started.