No spark, no communication with OBD port?

WGMMYSTIC

MEMBER
1994 GMC SONOMA
2.2L
4 CYL
2WD
MANUAL
153,000 MILES

All I did was change the spark plugs and now it has these problems. I have changed the crankshaft position sensor, and the coil packs, redid the entire main wiring harness as it looked a bit suspect in places, as well as changing the plug wires. Still no spark and no communication. I could really use the help; it is starting to get on my nerves.

5 Replies

KEN L

MASTER CERTIFIED MECHANIC
47,493 POSTS

The first thing i would do is check all fuses. This guide below will help, and I have included the fuse location as well. Also, I have included the engine wiring diagrams so you can see which fuses to test for power and a guide to help you test the grounds. If the power and grounds are good, I would replace the ECM which I have instructions for as well.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

and

https://www.2carpros.com/articles/how-to-check-wiring

You must change over the EPROM unit from the old PCM to the new one. Check out the images (below). Let us know what happens and please upload pictures or videos of the problem.

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Monday, March 6th, 2023 AT 10:02 AM

WGMMYSTIC

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3 POSTS

Already checked all fuses. I have a new ECM. Am I required to change over the eprom unit? I didn't think it would matter if it was from the same year and model with the same serv number on the ECM.

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Friday, March 10th, 2023 AT 10:44 AM

KEN L

MASTER CERTIFIED MECHANIC
47,493 POSTS

Yes, I would. Also check the power and ground inputs to the ECM using the wiring diagrams above. Here is the wiring diagram for the ALDL connector.

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Friday, March 10th, 2023 AT 3:20 PM

WGMMYSTIC

MEMBER
3 POSTS

Basically, what has happened today is that the ign fuse wire wasn't getting power, so we manually jumped it. It now has spark back for some reason even after we disconnected the manual connection, but now the fuel pump doesn't prime or run at all. Also, when we give the truck some fuel manually, it just spits and sputters and backfires trying to start now. When applying power to the fuel pump test lead under the hood the pump runs fine.

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Friday, March 10th, 2023 AT 3:22 PM

KEN L

MASTER CERTIFIED MECHANIC
47,493 POSTS

Did you swap the Eprom over? Also, I would check the power and ground sources to the PCM and if there are good, I would replace the distributor with a rebuilt unit. I would replace the ignition coil as well. These components trigger the fuel pump through the ECM. With the key on please test the remaining fuses for the ECM which you can see in the wiring diagram above.