reposting this from the s10 forum because im dealing with idiots. "electronics work perfect or not at all" yeah no. thats not how that usually goes

i went to fire my s10 up and drive it and it drove fine to the store and on the way back the digital dash started to flash on and off and switch units so i thought maybe it was the dash. and then i noticed the truck was revving itself in my driveway when i walked in to open the garage door. like hard revving. to 3k and back over and over and when it would rev down it would almost stall.
charging voltage is going crazy from 18-12 flashing everywhere inbetween as fast as my multimeter can see it.
does that sound like a dying ecm?
if anyones knows where the pcm relay might be let me know.

Don't shoot me if this answer makes no sense at all, but I asked ChatGPT about this. His answer:

Based on the symptoms described—especially the wildly fluctuating charging voltage (swinging from around 12V up to 18V) and the engine revving on its own—it’s more likely you’re dealing with an electrical power supply issue rather than a dying ECM. A failing ECM usually causes more consistent problems rather than rapid voltage fluctuations.

Here’s what might be going on:

Alternator/Voltage Regulator:
The alternator should normally produce about 13.5–14.5 volts when the engine is running. Seeing readings as high as 18V suggests that the voltage regulator (often integrated into the alternator) might be malfunctioning.

PCM Relay:
A faulty or intermittent PCM (or ECM) relay could be cutting power to the engine control system sporadically. This loss of power might cause erratic engine behavior, such as the rapid, unintended revving you described. On many S10 models, this relay is found in the under-hood fuse/relay box—often located near the battery. Checking this relay for proper operation or replacing it might resolve the issue.

Wiring and Ground Connections:
Loose or corroded battery terminals or poor ground connections can also cause erratic voltage readings and abnormal engine behavior. Ensuring all connections are secure and clean is a good first step.

Troubleshooting Steps:

Inspect Battery and Ground Connections:
Make sure the battery terminals are clean and tightly connected, and check all ground connections for corrosion or looseness.

Test the Alternator:
Use a reliable voltage tester to check the alternator’s output. If it’s exceeding the normal range, the regulator might be faulty.

Examine the PCM Relay:
Look in the under-hood fuse/relay box (near the battery) for the PCM relay. Check for any signs of wear, corrosion, or loose connections, and consider replacing it if necessary.

Check for Wiring Issues:
Inspect wiring harnesses for any frayed wires or poor connections that could be causing intermittent power delivery.

Conclusion:

The symptoms don’t typically point to a failing ECM on its own. Instead, they suggest a problem in the electrical system—most likely involving the alternator/regulator or the PCM relay. Start by checking your battery connections and alternator output, then move on to the PCM relay and wiring. This approach should help you narrow down and fix the root cause of the erratic behavior.

quote Originally posted by Cliff Pennock: Don't shoot me if this answer makes no sense at all, but I asked ChatGPT about this. His answer: Based on the symptoms described—especially the wildly fluctuating charging voltage (swinging from around 12V up to 18V) and the engine revving on its own—it’s more likely you’re dealing with an electrical power supply issue rather than a dying ECM. A failing ECM usually causes more consistent problems rather than rapid voltage fluctuations. Here’s what might be going on: Alternator/Voltage Regulator: The alternator should normally produce about 13.5–14.5 volts when the engine is running. Seeing readings as high as 18V suggests that the voltage regulator (often integrated into the alternator) might be malfunctioning. PCM Relay: A faulty or intermittent PCM (or ECM) relay could be cutting power to the engine control system sporadically. This loss of power might cause erratic engine behavior, such as the rapid, unintended revving you described. On many S10 models, this relay is found in the under-hood fuse/relay box—often located near the battery. Checking this relay for proper operation or replacing it might resolve the issue. Wiring and Ground Connections: Loose or corroded battery terminals or poor ground connections can also cause erratic voltage readings and abnormal engine behavior. Ensuring all connections are secure and clean is a good first step. Troubleshooting Steps: Inspect Battery and Ground Connections: Make sure the battery terminals are clean and tightly connected, and check all ground connections for corrosion or looseness. Test the Alternator: Use a reliable voltage tester to check the alternator’s output. If it’s exceeding the normal range, the regulator might be faulty. Examine the PCM Relay: Look in the under-hood fuse/relay box (near the battery) for the PCM relay. Check for any signs of wear, corrosion, or loose connections, and consider replacing it if necessary. Check for Wiring Issues: Inspect wiring harnesses for any frayed wires or poor connections that could be causing intermittent power delivery. Conclusion: The symptoms don’t typically point to a failing ECM on its own. Instead, they suggest a problem in the electrical system—most likely involving the alternator/regulator or the PCM relay. Start by checking your battery connections and alternator output, then move on to the PCM relay and wiring. This approach should help you narrow down and fix the root cause of the erratic behavior.

for this one unfortunately that doesn't help. i know its something going on with the signals coming out of the ecm. also i can't find the pcm relay on mine. it isnt in the factory location for any first gen s10 blazer. so im not sure at this point (its wired closer to a fiero than you might think. it's the same prom ecm)