baffled, still running rough.

[zman525]

Alright well i have a 76 280z pretty much bone stock and i cant get the damn thing to run right. At first i thought it was ignition related, so i have a new dist. cap, rotor, coil, wires, and plugs. Gapped the plugs properly and tested my spark. im gettin great spark at each plug. then i figured it may be injector related. so I tested to make sure i was gettin a pulse at each injector. then i used the classic stethescope to hear if they were firing and they all were. The engine sounds like is not running on all cylinders, or the the timing is way off. Ive adjusted the timing and even adjusted the valves for the hell of it. can not figure out wats going on. Ive messed with the afm and no luck either.

[FastWoman]

I'll bite.

Put a vacuum gauge on it. The needle should be steady and the vacuum strong. It won't be strong if your engine is missing, of course. However, it should definitely be steady. If it's bouncing all over the place, you could have sticking or leaky valves, which would definitely cause the cylinders to miss. The advice I seem to be getting for a dirty engine is to use Rislone. That would have been better than flushing, which I did, and which liberated incredible amounts of sludge all at once. (Gradual is better.)

Test the compression. Do all the cylinders look normal?

Pull the plugs, and read them for clues as to fuel/air ratio problems, oil, etc.

FAIW, I had major headaches with an old 1975's fuel injection system. Even if your injectors fire, are they injecting the right amount of fuel? How does your exhaust smell? Rich? Lean? (Again, what do the spark plugs tell you?) I ultimately found my AFM had been damaged from backfire, and the engine ran much better after I bent the metering flap back into shape and recalibrated.

There are lots of things that can cause these engines to act up. It just takes a slow, methodical approach to work through all the bugs. Then they run great!