3.4 Camaro has a miss

[big gear head]

I installed a '94 Camaro 3.4 SFI engine in my '84 S10 4X4 truck. It ran very well for several years, but for the past few years it's had a miss that I can't find. I've replaced everything in the ignition system, I've replaced all of the injectors, I replaced the cam (had 3 bad lobes), I've replaced everything that I can think of. I have a spare engine that I have been using for parts. Is it possible that the ECM is causing this miss? It has also started reving up when I start it. It didn't do that before.

[Firehawk94]

Is your check engine light on? See if you can pull any codes off of the PCM and go from there. Have you considered your crank sensor, cam sensor? If your PCM isnt throwing trouble codes then you might have some valvetrain issues. Instead of just throwing parts at it anymore than you already have try and pull the codes off of the PCM and go from there.

[big gear head]

No light and no codes. I've replaced the crank sensor and the cam sensor. I put a new cam in it. I've replaced all of the coils, wires, module, spark plugs, injectors, fuel pressure regulator, and anything else that I can think of. I have a spare engine, so many of these parts aren't costing me anything.

[Firehawk94]

Wow that pretty much covers everything. Run a comp. test on it and see what you get. If that checks out then pull out the trusty old vacuum gauge and see what readings you get. You may have a leaking intake manifold gasket, a weak valve spring, burnt valve, etc. and a vacuum gauge would point stuff like that out given that you know how to read one.

On another note, just a thought, I had just about the same issue with the bird in my sig. but my problem was alittle more than a miss...it was running erratic and misfiring like crazy, turned out to be the harmonic balancer apparently it plays a role in ignition timing on these engines, but I cannot say how because the crank sensor and cam sensor doesnt read off of the balancer. Maybe someone could educate me?

[big gear head]

Thanks for the reply. I'll check it out.

[geoffinbc]

The back of the balancer has a metal insert that is slotted. There is a sensor mounted to the timing cover just behind the balancer that reads it.

[big gear head]

I haven't changed that one yet.