Allanggg2

I apoligize ahead of time for saying/asking silly stuff. Just a typical backyard mechanic here.

I have been following a no start condition for a while on my 1995 z28. About 2 months ago it suddenly died on the highway, acted like the other times my opti went out. No warning lights, no codes. Got it home and fuel pressure was fine, but my spark at plugs was yellow, so I knew it was a problem with ignition. Long story short, I've checked all fuses, replaced the opti with a summit racing brand opti with literally zero miles on it, but a new coil and icm on, both acdelco oem parts. After installing the opti but before replacing the icm and coil, all the harnesses and connectors checked out according to shbox's website. ICM harness had 10vdc on a and d, 1-4vac while cranking on b, and continuity on c. I happened to take my icm to autozone and they tested it said it was bad, so I replaced both the coil and icm. I tried getting some "Thermal paste" from summit, but all they had and recommended to me was dielectric grease. I read on this website that some have used dielectric grease and were fine but some religiously recommended only thermal paste/grease, the stuff you used on the back of a cpu. I didn't have access to any of that so I just put the dielectric grease on there. Is there a problem with that and would it possibly make my car not start? Another problem arose after I replaced the coil and ICM. I started getting no vac at terminal B, which I'm supposed to have 1-4. While cranking it wouldnt go above 0.2 vac. Could the dielectric grease be a cause or just a faulty new part? During all this time the Opti harness has been fine. It's getting proper voltage and has a good ground, along with a brand new opti. I read on the shbox website, if im not getting 1-4vac on B, it's opti related; either harness, opti itself, pcm or any wiring in between. All my contacts on the harnesses don't seem to be corroded or damaged. Could I just have gotten a faulty opti straight from summits shelves? I've read it happens, but has never happened to me. Thanks for reading and bearing with me.

Injuneer

To condense that large paragraph into something easier to understand:

- the engine shut down. You scanned for codes, and there were none. Correct? Or are you just assuming there are no codes based on past Opti problems?

- you checked the fuel pressure and it was "fine". What, numerically is the fuel pressure?

- the starter cranks the engine, you have spark at the plugs (possibly weak), but the engine will not start. Are you sure you indexed the Opti correctly to the cam dowel pin?

- you first replaced the Opti, then when you first tested the voltage at the ICM pins, everything was in accord with Shoeboxe's guide. You replaced what Auto Zone said was a faulty ICM, and now you are getting negligible AC volts at pin B. Do you still have the (weak?) spark when the starter is cranking the engine?

- you should use thermal compound on the ICM, but using dielectric grease will not prevent the ICM from functioning correctly, at least not when the engine is cold and not starting. Best thing to do with the ICM is space it away from the head, as shown on Shoebox's site. At this point, using the dielectric grease is a non-issue.

Allanggg2

I scanned for codes while cranking and there were no issues found.

Fuel pressure gauge showed between 41-43 psi while cranking.

The first thing I did after I installed the new opti and no start was take the car back apart and double check that the opti is on there the right way. The opti screws sit a hair apart from the hole.

I have no spark at all from the coil when cranking. I put the coil wire back on and grounded it to the block and there was no jump, even with a very small gap.

I will get my hands on some Thermal paste after I figure this problem out, I hear the best place is radio shack or any computer parts store

Injuneer

Totally lost me with that one. What screws/what hole? Indexing simply requires that the cam dowel pin is inserted in the correct slot.

http://shbox.com/1/opti_back.jpg


The question on indexing was an issue only if you had spark, which you said you had. The lack of AC volts on the white wire from the PCM to the ICM (pin B) would explain no spark. Check the volts on the Opti harness connector. That's part of Shoebox's procedure, but you only mentioned the results of checking the ICM harness. Put the old ICM back on and see if that changes the results on ICM pin B.

A faulty optical module in the Opti would set DTC 16 and/or DTC 36. The important one is DTC 16, because that's the one that shuts down the fuel system. Also does NOT turn on the SES light. Guess you didn't check right after the engine shut down. Did you disconnect the battery at any point in your troubleshooting? DTC 16 (low resolution pulse) can set during cranking, but it has to be an extended cranking period, and it needs the high resolution pulse to determine the engine is rotating.

Allanggg2

I know that it's easy to know if you installed the opti wrong if the opti sits too far off its seat and isn't flush in the back and you have to push it in. I did not have that problem.

The opti connector was fine, I said in original post (as in voltages). I will double check again everything tomorrow, and put on my old icm, but idk what good that would do, since i'm checking the connectors pins with it disconnected from the icm.

I have not disconnected the battery at all, and check for codes regularly. I have not tried to crank for a while and see if it throws a code then. How long would say is "long"? I can hear the fuel pump prime and I have fuel pressure though.

Injuneer

OK, but that is not foolproof. Up to you.

Yes, I saw where you "checked out" the Opti connector, but you didn't quote the voltages. I have no way to know whether you checked the voltage or not. Sounded like all you did was look for damaged pins. I read what you posted very carefully, several times, but couldn't find the info.

At this point, you seem annoyed that I'm asking questions to get info to help you. You posted a huge paragraph that is extremely difficult to follow, and I made a major effort to organize the info, and use a systematic approach to work through your problem, step by step. So I'll drop off and stop annoying you. There are others here who can help you.

Allanggg2

I have answered questions to the best of my ability. I don't post this stuff often and have trouble using correct terms. If you interpreted that as me not wanting your help, I don't know what else you want me to tell you , and I'm sorry. You helped me out before on a very amateur problem and it got fixed. I don't know what I'm doing that's annoying...

stopthatman

After I swapped my opti, I found a problem with crossing the hot or ground wires on the coil. no start. It's hard to keep them apart when tightening. I made sure they were separated and rvoom it started right up after fixing that.

Pulling the small eye wires on the junction box and the one next to it and sanding with 600 and replace after electronic parts cleaner had a noticeable improvement in idle after that.