1987 Pontiac Fiero Missfire. Help?

[CHACHA]

I have a 1987 Pontiac Fiero that has been misfiring since I bought it. I have checked and replaced many things. It is NOT the spark plug wires, spark plugs, ignition coils, ignition module, crankshaft positioning sensor, MAP sensor, fuel filter, O2 sensor, injector. No vaccuum leaks, spark plugs ARE gapped correctly. What else could it be?
Compression is normal

 

[doane_nut]

Check the compression in each cylinder.

 

[millersoftucson]

mystery miss fire in fiero

Check out the harmonic balance pulley. It has a magnet in it. I spent a 1000.00 trying to find a miss fire. It turned out the balance beast was all messed up. Got a new for 100. A tell tale sign is a wavering timing light. I thought it was the distributer.

 

[millersoftucson]

I was wrong

I was wrong about the harmonic balancer, sorry. Turns out the two piece beast was broken and freely spinning making setting the timing difficult. I still have a miss fire. I just don't want to check the compression for fear of a bad engine. I can tell you I have replaced the MAP, coil, TPS, Ignition module, pick up coil in the distributer, replaced all vacuum lines, replaced fuel injectors and plugs and wires and air cleaner and IAC. All to no avail. Have discovered that this newly bought beast had a completely blown out cat and all that was blown out is sitting in the muffler plugging it up. Have new parts coming and will report back to all. My only thought is that the O2 sensor (new also) is reading a situation of increased back pressure and may be sending the ECM mixed information. That is the last $1000.00 I am going to spend on the beast. This morning I am going out and cutting more vacuum line to cover all the spark plug wires. I am also pulling out the ECM in between the seats and cleaning out the harness points, re doing the ground fittings and pulling the PROM chip and checking for bad prongs. I have a stock PROM coming but research indicates it is for an automatic and I have a 4 speed. I will keep all posted.

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[millersoftucson]

misfire fixed, an update

Found the problem. I had rebuilt the distributer and it made no difference so I moved on to other items. In the back of my mind I just didn't think much of the OEM distributer design. If you but a rebuilt one they send you the same darn design.There are not many (one) new, not rebuilt distributors with a better design, frankly far superior design. It is a Richporter model GM17. I slugged it in to the beast just kind of close to where the other one was and it started up and ran great! Lord knows how it would run with it timed to 10 degrees BTDC! What a difference. It is available through O'Reiley for about $125.00 and free shipping. Worth a shot if you are at wits end.