So ive read about 50 forumns and cannot figure this truck out. Was running great then died at a stop light, code reader would not connect to the pcm. i pulled the plug on the pcm to find oil in it and the pcm itself, also oil in the big block connector on top of the intake. Ive sprayed electrical cleaner and blasted out these 2 connections and still have no communication with the pcm and my code reader. I also have a 1999 3.0 ranger that i swapped my pcm into after getting the oil out of it and my reader will connect to it so im assuming the pcm is still ok. Does anyone have any ideas on what i should do, im about ready to push this thing into a lake.

 

what happens when you turn the key? any lights, anything? maybe a ground cable? or positive cable? is the power to the ECU? what year is the truck?

 

Ive got lights, i checked all the grounds i could see and they look fine. ive got power at the pcm, its a 2000 3.0

 

when you try to start does the CEL go out? my first guess would be crank senso but with no power to a code reader? there is a relay that goes to the ECU not sure what one. maybe with key on ck coil for power. ithink it works by grounding from the ECU.

 

I dont get a cel when i turn key or crank, whats stumping me is that i cant even read any codes off of the obd port. I checked the fuse and swapped a known working relay that powers pcm.

 

ok so no CEL with just key on. humm. time to do some research. im pretty basic when it comes to electrical . how about ignition switch?

 

heres what i found. can you hear the fuel pump turn on when the key is turned?

If an ECU (Engine Control Unit) isn't receiving power, it can prevent a car from starting or functioning properly. Possible causes include a blown fuse, a faulty ignition switch, or a loose wiring connection. Also, the ECM power relay could be malfunctioning, preventing power from reaching the ECU.

1. Battery and Fuses:

• Check the battery: Ensure the battery is properly connected and has a sufficient charge.
• Check fuses: Inspect the ignition fuse and any other fuses related to the ECU or engine control. A blown fuse will need to be replaced.
• Check wiring connections: Ensure all wiring connections to the battery and fuses are secure.

2. Ignition Switch:

• A faulty ignition switch can prevent power from reaching the ECU.

3. ECM Power Relay:

• The ECM power relay is responsible for switching on the power to the ECU when the ignition is turned on.
• If the relay is stuck open, the ECU won't receive power.
• 
  4. ECU Wiring:
• Check for loose or damaged wires:
  .
  Inspect the wiring harness for any loose or damaged wires, especially those going to the ECU.
• Check for corrosion or rust:
  .
  Ensure there's no corrosion or rust in the wiring or connectors, which can disrupt the flow of electricity.
• 
  5. Other Potential Issues:
• Faulty sensors: While less likely to directly cause a loss of power to the ECU, faulty sensors (like the crankshaft position sensor) can sometimes cause the ECU to shut down or malfunction.
• ECU itself: In some cases, the ECU itself may be faulty and need to be replaced

Troubleshooting Steps:

1. 1. Check the battery and fuses:
   Start by verifying the battery's charge and condition, and inspect the fuses related to the ECU.
2. 2. Inspect the wiring:
   Carefully check all wiring connections, looking for loose or damaged wires.
3. 3. Check the ECM power relay:
   If you can access the relay, you may be able to check its condition and replace it if necessary.
4. 4. Consider other potential issues:
   If the above steps don't resolve the problem, you may need to investigate other potential causes, such as faulty sensors or a bad ECU.

 

I did all of that except swap the crank sensor, i dont see how that sensor being bad would cause no communication with the pcm, is that a thing with these trucks?

 

im pretty sure its ok the crank sensor.. you said that you have another PCM. it probably wont work because of PATS but it would light up the CEL i think. if thats the case and it lights up the CEL i'd look into a PCM. look into how to replace the ECU with PATS. you need to pair the key to the ECU.

 

I swapped my ecu into another truck and it was able to read fine but not start because of the pats. Since it read, it leads me to believe that theres an issue with the wiring somewhere on my truck.

 

I suppose you could verify that by putting the ECU from the other truck into your truck and see what happens. If the check engine light does not come on for sure you know it is a wiring problem or definitely something electrical

 

I’m kind of guessing that it’s a ground? Maybe the ECU just isn’t grounded properly? I’m not sure how to check for that.

 

SOLVED, turns out the vacuum sensor on the front of the intake was shorting out and causing the pcm to not be able to communicate. I havent seen this problem on any other forums ive read so hopefully this helps someone out one day.

 

good job!

 

PCM diode. Or the PCM relay, fuel pump relay, or the associated fuses. Without that PCM/FP circuit intact you would get no CEL with KOEO. It will crank until you drain the battery and never get fuel OR spark. The old 50/50 starting fluid test is mostly useless here. Sounds like an intermittent electrical component failure.