'no spark' advice needed

[mk1turbo]

How's it going. I have searched around for previous posts that address my issue, but wasn't able to find anything that helped.
I'm working on an '86 NA 5spd that wont start. It ran fine w/ no issues; stopped for gas and it has not started since. I've narrowed it down to a spark issue. Its had a pretty complete tune up months before and has consistently ran well since.
When testing, there is occasionally random, but weak spark - but never enough to get the car running. I just recently replaced the power transistor from the original to the PRW-2 upgrade - unfortunately it didn't change anything. I don't have any spare parts for the Z but I did try out a known good coil from one of my supras (similar design), but again, no change.
I believe its probably the crank senor/ distributor at this point, but I'd really appreciate any advice that could help me figure this out.
Thanks!

[jdmlegends]

I would test your Z31 ignition coil if you still have it with a multi-meter or ignition coil tester as weak spark indicates that your coil may have gone bad. Try to see if you can get a hold of a used one too.

[mk1turbo]

I appreciate the help. I did test the coil w/ a multimeter and it tested ok, but if I understand correctly, that only shows the primary windings are ok, tho I may have backwards.
I did rig up a good coil - not an exact replacement, but similar design - just to see if it changed anything but everything seems to be the same.

[mk1turbo]

I bought a new stock coil and just installed it. I checked for spark and it there was initially a decent and consistent spark - afterwards, I went to start it and after a few tries, it ran for a moment (maybe 10-15 seconds), and then died out. After that, though it sounded like it was about to start, it wouldn't start again. I checked for spark again, and it was back to mostly no spark - just a random, occasional spark. So I believe the new coil didn't change anything, but I can eliminate it, and the power resistor, as the issue.

So would anyone have any suggestions of what is the next most likely cause of my issue? I am still leaning towards the crank sensor/ distributor - other than the ECU itself, I'm not sure what else it could be.

[mwolvinm]

Have you tried cranking it with the distributor cap off to ensure everything is spinning as it should? Also, what about spark plug condition and gap as well as the contacts on the cap and rotor?

[mk1turbo]

Yes, I did crank it over w/ the cap off to rule out the belt, etc... everything was ok.
Had a complete tune up a few months before this - so new cap, rotor, plugs, wires & fuel filter were done then, and it was running great afterwards; and now have just replaced the power transistor and coil.
Thanx for your input - I really appreciate any help trying to figure this out.

[Dunkine]

Did you flip the wires when you did the PRW2 upgrade? Did you check the ecu for codes?

[mk1turbo]

Thanks for your reply.
I followed the info from this http://www.xenonzcar.com/z31/prw2.html from the "updated transistor ???" thread.
I've had the car run for a few seconds since I did the coil & power transistor; though it didn't run long, it ran smoothly - so I feel pretty confident that the PRW2 upgrade is good.

I did check for codes after narrowing down that it wasn't fuel related and that it was a spark issue - I cant remember the codes but they weren't related (#31 IIRC)...

Has anyone had issues w/ the crank angle sensor/ distributor? I cant think of anything else it could be (other than the ECU itself). Replacing the coil and PRW2 was cheap and easy, so I have no regrets that I replaced them, but it would really suck to buy a distributor or ECU and it end up still not running, so I would like to be more certain of the problem before going any further.

[mk1turbo]

Last attempt to get any feedback or suggestions from anyone about what might be causing this spark issue - I am not sure how common ECU failures are, but I cant think of it being anything other than the crank angle sensor/ distributor at this point.
Thanks!

[jdmlegends]

It's either CAS, or Ignition coil and if it's not those it's the ECU. ECU failures on these cars are uncommon, but they do fail on occasion for one reason or another. Afterall, they are all over 30 years old.

[mk1turbo]

Thanks - I just replaced the coil (and power transistor) - so I'll try a new CAS.
I have alot of experience w/ Toyotas from the '70's-'00's and I've never had an ECU issue - its almost unheard of (short of owner errors of some type), and I would of thought the Z to have similar reliability w/ the ECU.
Thanks again