85 Z 305 TPI Has intermittant fireing problem. One day I will fire it up and it runs great. The next time it misses severely then it may not start for a month. There is no patern. I have narrowed it down to not getting spark randomly when it is missing using a timing light. ANY help would be greatly appreciated. Has too much new on if to list. Including PCM and Chip. Same problem as when I started. No codes in it. Thanks, Aaron. rocket@tctc.com

I wouldn't rule out inadequete fuel pump pressure or a clogged fuel filter and/or injectors!

Battery condition?
Distributor? May be a reluctor problem inside?
All electrical connections on solenoid clean? There are a couple fusible links attaching the solenoid stud.
Spark plugs wet with fuel? Dry them or swap them out.
Cold start injector working?

aaron,
just to be sure i understood your post... at the times it wont start there is NO spark??
if that is the case..and it being so intermittent..if the distribor pick-up coil cks good..900-1100 ohms..and module is good... i would be looking at loose grounds.or poor connections at distributor....or ecm..
many times at our shop we have traced back to these kind of issues...
kevin

Fuel Pressure is within spec. New filter, and remaned injectors by Linder Tech. Batt is excellent even tried a new one just in case. The dist is a remaned A-1 Cardone unit, new coil, wires, and plugs. They do get wet when it wont start. The cold start injector was cleaned and checked also by Linder Tech. Have to check the solenoid yet. The ECM is remaned by AC Delco and the prom is a Hypertech because no stock one is available. Checked wireing to ECM looks ok EST wire to ECM has continuity. Added a ground from batt to Block 4 ga no change, Added ground wire from ECM case to body no change. ALL sensors replaced except EGR temp and TPS tested ok. Tried new MAF no change. Timing chain has approx 4 deg slop both directions, Compression is good. On a currious note the Tach is reading 2500 to 3000 rpm at Idle that sounds ok except when it is missing out. Just tried something new. Let the car warm up then unhooked the bypass connector. The timing is still dead on at 8 but it still misses spark randomly (again tested with a timing light). Does this rule out the ECM and wireing? Thanks again.

I would check TPS and MAF sensors it sounds like a fuel system issue to me. Also how about your converters

Timing should change between being bypassed and not bypassed. Use another timing light to be sure and mark the harmonic balancer if you don't have an adjustable timing light.

Thanks again for all your help. Yes the timing does change when the with bypass connector is unhooked. What I am refering to is the pulses from the light randomly stop flashing briefly when the engine misfires. In other words it would appear that there is no spark being sent to that plug at that moment. This happens with and without the bypass connecter hooked up. I thought fuel system as well at first that is why it has been overhauled. Didn't change a thing.

Three ideas come to mind - okay, four ideas:
1. Distributor faulty - but its a reman unit. Either reluctor is too far away, bad pickup coil - s/b around 1K ohms, module has given up or button between coil and rotor has become a high resistance.
2. ECM - takes rpm reference and splits it for ign and injector pulses. If dist is problem, then both systems are affected.
3. Wiring problem(s) between ECM to engine circuits.
4. Faulty power going to distributor.

Sounds like Mass Air Flow sensor or the Cold Start Injector to me. I know you are "seeing" misses with the light, but that problem sounds like a fuel/timing issue. We had similar problem with my 88 IROC years ago, fixed with a new MAF sensor. Now that my son has the car (after getting the salvage title...lol) it started doing it again. Cold Start seems to be sticking open and flooding, which you can smell coming out the exhaust. Car runs totally erratic and misses horribly, but then the next day starts fine and runs great. New motor only has 20k miles on it, but the TPI setup was reused.

-shoe