My friend just put heads and cam on his 94 camaro and his car has a bad miss/stumble above 4000-4500 rpm. It will hardly even pull past 4500 rpm. It feels like it runs real good up until that point. He had some high rpm problems before, but during the install he also replaced the opti with a vented unit, changed the spark plugs and replaced the plug wires. We have tested the fuel pressure and it stays steady under acceleration, even during the missing. Any help would be great as we would like to see just how hard it pulls all the way through the powerband.

 

Maybe something was not installed right. I think I heard about problems when switching to a vented opti, but I can't remember for sure.

 

it could possibly be the plugs or wires. i have heard from several people that have had new faulty plugs/wires. also, make sure you have them in there tight. many times a bad coil will give a high rpm miss. also, tuning may be required with heads and a cam.

 

high RPM misses are usualyy related to the coil, try swappin it out with urs to see i f thats the problem.

 

A misfire can be either electrical, fuel, or mechanical. It could be from a serious vacuum or intake leak. These guys are right, it could be the ignition. Start the car and look very carefully at the plugs at night. You're eyes may take a minute or two to adjust. It also helps if the car is on a lift or if you can get access to get a good look at the plugs while the car is running.

Sounds like a the porcelin on the plug could have been damaged (dropped)...

There are a number of reasons, but it helps to check. Sounds like the fuel system has been checked.... keep us posted.

 

see if the glass on the plugs are cracked. This happpened to me (the vato-zone guys said I torqued them down too tight) it that happens, it will actually arc through the glass to the head.

 

Exactly, the porcelin/glass must be unbroken... even hairlines are trouble. Just look under the hood at night and let your eyes adjust to the darkness...

 

Well, good news and bad news. We redid some grounds on the coil assembly and went for a drive and the car pulled real good and seemed like it was running pretty good. Then all of a sudden it just died. We could get it going again, but as soon as you let off the gas it just dies. It also has sort of a knocking sound coming from the drivers side of the engine. Also while the car is running, if you floor it, it pulls like a four cylinder. We are thinking maybe there is a really loose rocker which is robbing us power. What do you guys think?

 

Still sounds like ignition....

Fuel and your whole engine would be out, not just the driver's side. A fuel filter that is clogged could cause some drivability issues.

Mechanically, a rocker arm would make a rattling noise. That could be it but should still idle with only 7 cylinders.

Are you getting any codes?

 

Well it turns out that we must have fixed the problem with the grounds and coil, but on the test drive the car blew a rod bearing and thats why it no longer idled. I heard a slight knock last night when trying to find out why the car wouldn't idle and today after some more diagnosis and a loud squeal it was confirmed to be a bearing. That really sucks. I can't believe the engine blew from a couple of revvings to 6500! The car never had good oil pressure though(maybe 10 at idle and 20 with acceleration) and i suspect that there may have been something wrong already or that the low oil pressure caused the bearing to go at high rpms. Who knows though.

 

Yeah, low oil pressure is a good indicator of a bearing going bad... if it is caught ahead of time. How bad is the bearing? Time to pull the crank?