Hello everybody, first time poster here on the forums.

I have 1997 F250 Light Duty With the 4.6L. It has approximately 208,000 miles on it. A few days ago I was driving down the road when the engine began to stall upon acceleration and then it would "catch" itself and keep running. It done this a few times before it died completely and would not restart. It will crank but not start.

To begin diagnosis I checked the fuel pump which was not getting power. I moved to the fuses regarding the fuel pump both under the hood and in the cabin. None were blown. The fuel pump will run if I jump the relay which tells me the fuel pump relay is not getting the ground signal from the PCM. I then focused on the PCM. The CEL does not come on anymore when turning the ignition on nor will an OBDII scanner communicate with it. I assume it is either faulty or not getting power. I've never experienced a computer failure before so I am leaning towards a bad power/ground circuit. The PCM fuse under the hood has 12V on it and I've switched the PCM relay around as well with no luck.

My question is what is the best way to check and make sure the PCM has power and ground? The connector is pretty deep in the engine. Just unhook it and probe the connector at appropriate pins? Also where does the PCM get its ground on the truck anyways?

Thanks, Adam

 

The best way is to verify that the components that are supposed to do that are actually doing their job.

Did you check to see if the PCM Power Relay is energizing when the ignition is is turned from OFF to RUN? If that doesn't happen, nothing else will work, including the PCM.

There are easier things to do first, that would be the last resort.

Grounding stud on the firewall near the PCM.

 

How would I go about making sure the PCM test is energizing? It clicks when the ignition is turned to run. Also, 2 of the pins, (30 and 85 maybe?) have 12V present with the key to run position.

 

Pop the connector off the MAF and measure between the red and the black/white wire with the ignition switch in RUN. If you have battery voltage, then the PCM Power Relay is supplying power and the problem of the PCM not powering up is isolated to either the wiring to the PCM or the PCM itself.

On the PCM's connector, that red wire's circuit should also supply power to pins 71 & 97. Ground is on 5 pins. See attachment.

 

Thanks projectSHO89, I got it fixed I believe. The ground on the firewall was very corroded and weak. Cleaned it up really good and the truck fired right up.