So after completing ShoeBox's ICM test, I've discovered that my ICM pigtail connector terminal C is not grounding (even after replacing the pigtail). It's reading about 7-9 ohms. Theoretically, can't I just splice another solid ground into this terminal C wire to see if that resolves my intermittent crank but no start condition? If so, can I just ground it to the head as well? During my issues, I've been getting DTC 16 (low res failure) and DTC 36 (high res failure) with both a rebuilt MSD opti and brand new AC Delco, which I'm currently running.

 

Did you check your meter to make sure you could get a zero reading to ground from it? 16 and 36 are pointing to the opti-not the ICM. Have you looked over your whole harness and connections at the PCM? Terminal C grounds right on the engine head at the coil stud.

 

A reading of less than 1 ohm could be a poor connection from the meter lead to whatever you are connecting it to, or corrosion under the terminal if you are measuring from the connector pin to the head or stud. For all practical purposes, you have a ground.

 

Correction...I am getting a consistent 7-9 ohm reading from terminal c to ground on the icm connector. I had the range wrong. I've also tested the positive and negative leads together and get 0 ohms, so they check out. Please advise.

 

Check that ground wire from end to end.

 

Updates:
Since I wasn't getting a good ground to terminal C on the ICM connector, I spliced in an additional ground wire to the head coil stud and got ~1 ohm (essentially a decent enough ground). I proceeded to the Opti harness test at the pcm harness side and got the following 5vdc on A & B, 11.75vdc on C, and ~15 ohms on D! It looks like I have a PCM grounding issue, but where should I look? I suspect the ground wire at the lower passenger side block, but are there any others?

 

...just to confirm, the opti harness test is done with the key on even when testing terminal D to ground? As mentioned earlier, I get 15-20 ohms on opti harness terminal D when testing with the key on, however, when testing with the key off, i get 0 ohms as within spec. Anyone please advise. Thanks.

 

As the opti harness tests says...Key ON. That's the spec.

What are you using as a ground reference when doing these tests? The PCM grounds at the block by the starter and at the coil stud (where your other ground seemed to be bad-maybe that is a hint?).

 

When conducting the opti harness test, I've used the battery as a ground, as well as the throttle body (both provide similar results). I re-did the connection to the engine ground by the knock sensor anyhow. Now I have extemely slow cranking (almost sounds as if the battery is about to die), but the car eventually starts every time...or at least has been starting since I've re-grounded the wires. The alternator charges fine while the car is on. I guess I'll need to confirm that the starter connections are tight and clean and see what readings the opti harness gives for ground to see if I've made any improvement. I almost am ready to get a new wiring harness...

 

Updates: I was able to effectively improve the PCM ground by directly adding a ground wire from one of the PCM torx perimeter bolts to engine ground. This was confirmed by checking the resistance on terminal D of the opti harness with KOEO (went from ~15 ohms to ~4 ohms). I'll see if adding a thicker gauge wire makes the ohm value decrease to < 1 ohm. I know this probably isn't the best way to resolve a pcm grounding issue, but it seems to be working. Anyone else done this? Later, I'm going to go into the 4 PCM ground wires and test for continuity (Red Connector Pin 2 & 18, Clear/Gray Connector Pin 32, Blue Connector Pin 1)

 

Were you ever able to find the root cause of your issue? I am having an issue where the engine turns over for a 30 seconds and will eventually start.

 

Try an e-mail. "lightskindwonder" has not visited the site since last July.

Left click on his screen name, and it will give you a drop down with "send e-mail" option.

 

GMH94Z28 - Have you tested the fuel pressure?