ESC/EST issues

[VIKING_MECHANIC]

So the 89(K1500, 5.7[for @Schurkey]) isn't starting and I'm hoping you guys can help me with my diagnosis.

Thursday after work I pulled my truck in to try figure out an issue where it will die under load(only in gear though). When driving or sitting still, if I revved the engine then completely let off the throttle, it would die as it came back down to idle. Both my boss and his retired mechanic(that lives on site) both told me there's a good chance it may be the IAC based on what i told them.

So I pulled it in and disconnected and pulled off the IAC, cleaned it a little(wasn't really that bad) and put it back in. Went to start the engine and just cranking. It was 8pm at this point so I went home.

Came in today and my coworker was able to help be figure out it is a spark issue as the coil was not sending spark to the distributor. Kool. Ordered a new one, installed it annnnnd same thing. No spark. Could be a faulty new coil, but I'm doubtful, at least for now. I tested both with a spark tester.

I remembered from yesterday that It had what I believe was code 42, but not positive as I wasn't paying attention and just skipped past it looking for any code related to the IAC/TPS I had messed with yesterday.(using our Tech 1).

So back today. I looked up the code and wiring diagrams and turned my attention to the ESC. I was getting 12v and both grounds using my power probe, so that leads me to believe that the wires in the harness are in good shape and the module has failed. I tried a ESC module from a TBI truck in our yard but same thing. Just cranking. So either that module just happens to be bad or there's something else going on.

From what I understand, the ESC module is an SSD, so is there a way to test it? I'm also cautious of that ICM on my new distributor may have took a crap. Is there a way to test the ICM as well?

Also, i was able to confirm that the coil was getting 12v and ground at the connector, so that's how I eliminated it.

Any ideas on what I can do next?

 

[Erik the Awful]

How's it run with the ESC unplugged?

I'd suspect the ignition module before the ESC, especially as I ran without an ESC for a while.

 

[VIKING_MECHANIC]

How's it run with the ESC unplugged?

I'd suspect the ignition module before the ESC, especially as I ran without an ESC for a while.

It won't start with or without it connected.

The ignition module is my next suspect to check later today.

 

[Schurkey]

89(K1500, 5.7

Is there a way to test the ICM as well?

Not easily like on the older 4-pin modules. Will take some contortions. And I don't have a photo suitable for TBI distributors. I have one from the old 4-pin ignition module, though.

You need to disconnect the pickup coil wires from the module. That's a 2-pin connector on the back-side of the TBI module. Leave the other wires connected.

Connect an incandescent-bulb test light lead, (preferred for safety) or a jumper wire to a power source. The + terminal of the battery, or the output terminal of the alternator. Connect your spark tester to the distributor end of the coil wire, and ground the spark tester as appropriate. With ignition ON, but the engine not running, touch the test light probe or the jumper wire to one of the two terminals on the module. When you REMOVE the probe or jumper, you should get a spark if you were touching the correct terminal. I'm not sure which of the two terminals is the right one.

On the old 4-pin module, it was the smaller one marked "G" and connecting to the Green wire.

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[VIKING_MECHANIC]

Not easily like on the older 4-pin modules. Will take some contortions. And I don't have a photo suitable for TBI distributors. I have one from the old 4-pin ignition module, though.

You need to disconnect the pickup coil wires from the module. That's a 2-pin connector on the back-side of the TBI module. Leave the other wires connected.

Connect an incandescent-bulb test light lead, (preferred for safety) or a jumper wire to a power source. The + terminal of the battery, or the output terminal of the alternator. Connect your spark tester to the distributor end of the coil wire, and ground the spark tester as appropriate. With ignition ON, but the engine not running, touch the test light probe or the jumper wire to one of the two terminals on the module. When you REMOVE the probe or jumper, you should get a spark if you were touching the correct terminal. I'm not sure which of the two terminals is the right one.

On the old 4-pin module, it was the smaller one marked "G" and connecting to the Green wire.

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I took the ICM to autozone and had them test it as I was expecting it to fail. Tested good according to the machine(tried 4 times).

I don't have an incandescent test light but i do have a power probe if that will tell me anything? I could also test the pickup coil for resistance with a mulitimeter couldn't I?

From some research, I was able to eliminate the ECM as a possible issue since the injectors fire during cranking.

Just out of curiousity, disconnecting both the IAC and TPS without disconnecting the battery and moving the harness around(to get it out the way), that wouldn't prevent the engine from starting even if there was some sort of short inside the harness?

I say that because of this snapshot I took of live data using my bosses Solus. Notice the Volts for TPS and position of the IAC. Neither one changed when I tried to manually influence it.

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