Hello all,

I have an 1990 dakota that has been sitting for 10+ years or so. Like most vehicles it was running when parked. After reading the service manual (section 14-43, found on the FAQ page) and perusing the internet, here is the story thus far:

• Manually turned it over, threw in a battery and some fresh fuel and tried to crank it, which it did, but there was no fuel or spark.
• Checked the ASD relay, verified the relay was good, but found no ground coming from the PCM. Learned the PCM only sends ground when a valid signal is received from the distributor pickup.
• Checked the distributor pickup connector for 8V reference (PCM pin 7), only receiving 2.1V.
• Additionally checked the 5V reference (PCM pin 6) which is used by other sensors, only receiving 1.6V.
• Backprobed the PCM connector at pin 7, 6 with same voltages 2.1V and 1.6V.
• Checked the PCM power/grounds. pin 3 had 12V from battery, and 11, 12 - ground connections were grounded.
• Checked PCM J2 supply on pin 9 from "key on". Was receiving 12V.
• I unplugged all the sensor connectors to the PCM in case there was a short to ground on the reference lines, same results on above tests.
• Decided to try and bench test the PCM to eliminate any potential wiring issues, so hooked up 12V to pins 3, 9 and ground to pins 11, 12 out of the vehicle to simulate "key on". I received the same volts on the 5V and 8V reference feeds as in the truck.
• At this point I was thinking I needed a new PCM, but discovered that some people had success replacing the 3 capacitors on the PCM, which can go bad.
• I replaced the capacitors (though I didn't see any burn marks or exploded capacitors on the board) and reran all the tests, same results/voltages as before.

This is where I am now.

• Did I do the bench test correctly?
• Are there any other inputs to the PCM that can affect those reference voltages? My assumption is that the 12V input from the battery (pin 3) is somehow stepped down to 8V and 5V for the reference lines.
• Is there anything else on these boards that can be replaced that affect the reference voltages (resisters, voltage regulators, etc)
• Is there anything else I can try before replacing the PCM?

I appreciate any assistance, thanks,

Alex

 

There are likely step-down transformers, or fat resistors to bring 12 volts down to 5, or 8. Unfortunately, I have never seen wiring diagrams of the inside of the PCM...... Replacement is likely going to be your best option. See if you can find one in a local yard, that will take it back, if it doesn't work.