OK, here's what I got, I just bought a 95 Z-28 with a 383 in it with the LT-4 hot cam kit in it. The car runs great up to 5500 RPM's then it starts to miss and backfire. Acts just like its hit a rev limiter. I took it to shop and put it on a scope and all the vitals looked good, tested the vacuum, fuel pressure, and O2 sensors too. The tech took a look at the programing and the rev limiter is set at 6500 RPM's and everything else looks good. What he told me is I should hook up a fuel gauge and see what its doing at WOT. But said he was 99% sure it is the Opti. He thinks its indexed wrong. I was wondering what you guys think. It sure is a lot of work to change the Opti, and I would like to make sure that's what it is before I do it. Any info would be of great help.

 

Check the coil wire.

 

Thanks, I will check it. Does anyone else have something to add?

 

I just recently have had this problem too. So I'm gonna tag along. I have a new opti, coil, wires, plugs. I think I may have a problem with my ICM or I am not getting enough fuel. I should have upgraded my injectors a long time ago, but I'm poor.

Heads and Cam on stock injectors = problems up high

 

Try a fuel filter first see what it does....

 

Thanks, I will give it a try. Keep them coming I'll try all the easy one's first, because next weekend were going to try the Opti.

 

Just a thought, but did you check to see if the rockers were adjusted properly?

 

I was hoping no one would bring that up. I just readjusted all mine again. I know that they are correct, but I didn't have this problem before the readjustment...

I think I may have some mildly bent pushrods

 

Found my problem. Yesterday I started to put a new Opti in. After we got the old Opti out, we noticed that the cam dowel pin was to short so the Opti was being driven by the cam bolts. It was putting the Opti out of whack by more then a 1/4". Looks like the guy who installed the cam drove the dowel pin in to far or cut it off (what a moron). We were unable to pull the dowel out so last night I installed a new Hot Cam. The car runs great now without a miss. I hope no one else has a short dowel pin because I know no one wants to change their cam but I thought I should let everyone know what my problem was.

 

WOW!!! I’m glad that you found your problem, but that is a pretty strange problem. At least you found your problem before you dumped $800-$1000 in miscellaneous parts and driving your car for a couple of months not knowing what the hell is wrong your car.

 

Ya, but it still sucked. The hot cam in the car was only 6000 miles old, so I had to buy a new one, and while I was there I changed to old Opti because it had 61K miles on it, and I wasn't going to go back there. Then of course I had to pull the water pump so I had to change it to an electric pump. So it still cost me a chuck of change, but it could have been a lot more. But I’ll take the cam to a machine shop and have a new dowel installed and see if anyone needs an L-4 hot cam.

 

Shoulda put more than a hotcam in the 383 while you had it apart.

Had to say it. Glad you found the problem though.

 

I thought all LT1’s had electrical water pumps?

 

No, they have a drive shaft from inside the motor.

 

From the moderator... thanks for coming back and updating your thread with the fix to the problem. So often the people fix their problems with the help of the guys on this board but don't take the time to updat the thread with exactly what they found to fix it! Just wanted to say thanks for coming back and updating the topic