Was the reading in post #13 made with the ignition key set to OFF or not? If not, the reading is invalid.

I cannot read the range setting on your meter. What was it set at? If set to too high of a range, the reading might be normal.

Did you repeat the resistance reading check directly on the PCM between pin 91 and signal ground (have to look up the pin #)?

Any replacement PCM, should one be needed, would have to have the PATS system reprogrammed, otherwise, it will never start.

 

Post #13 It was set to 200 Ohms (lowest setting) and read .3 Ohms to ground and Toned ground when I set it to short detect. The key was in the OFF position.

Post #14 It was set to 200 Ohms again and read open. I cycled through all the ranges. That pin is where Red/Grey hooks into the PCM Harness. I couldn't tell you the number cause I didn't see any labels

I'll double check with Key to ON/RUN position and see if the PCM grounds those signals when it has power removed.

I found a 00 F150 5.4L in a nearby junkyard. Do you think the wiring harness would be a direct swap?

 

Okay, with that additional info, the readings do indeed point to an internal short in the PCM. My bet is a failed capacitor on the 5 volt regulator's output or the 5V regulator itself.

Just a reminder, do NOT use an ohmmeter in a circuit that has power, it will, at a minimum, give you incorrect readings. Worst case, you'll need a new meter.

With the additional information filled in, I don't see anything that indicates a need for a harness.

 

Haha Thanks man. I'm an electronics technician and figured out that one the hard way a long time ago. Luckily the fluke I was using had internal mini fuses.

So I got a used PCM on the way for $85, I guess I'll need to take it to the dealership to get the new PCM reprogrammed. Or is there any way to do it myself? I'm incredibly handy with electronics. Actually... I might just try to replace the capacitor once I get the new one programmed and working.

Thanks again for all the help SHO I'll keep you updated.

 

Yes. Android device + BT adapter + Forscan app (with free extended license). If you already have the tablet or phone, you 're looking at an investment of about $25.

 

Oh really? Already got the Bluetooth obd2 now I just need that app. Does it have up to date ecm firmware?

 

Don't need that.

 

Ok so the app will allow me to program my ECM with my mileage and such?

 

No, that isn't necessary. Mileage is stored in the cluster, anyway.

You'd have to check into the features of the app, all I've ever used it for was PATS programming beyond its basic scanner functions.

 

What exactly is pats programming? From what I was reading it sounded like that was for recording microchipped car keys

 

Oh wait! I get it after looking up the acronym lol passive antitheft system.

So it's to allow me to reset the antitheft and prevent a no start condition.

I need to buy another micro chipped key because apparently you must program two.

 

Can I just buy these?

2 KeylessOption Replacement Uncut Ignition Chipped Key Transponder Blank Compatible with 4C https://www.amazon.com/dp/B00KTJ872U..._dmc1xbHA8SSGT

 

***** THIS IS CONNECTOR C120******

So I did some more digging tonight, and took apart the connector picture below. The grey IAT sensor wire should land on ECM connector pin #39 the wire stops at the "B" Side of this black 42 pin connector.


Taking it apart, I can see that inside connector "A" there is no pin landed in slot 40 as it is on the "B" side.

I traced ECM connector pin #39 to AB connector A side pin #27.



Does this mean someone replaced the wiring harness with the wrong one? Should I be looking for a wiring harness?

The Engine Control Sensor harness part number is 9D930, but ill be a ******* if I can figure out what the rest of that part number should be. I friggin hate how Ford labels these damn parts.
http://www.fordparts.com/Commerce/Pa...rd&model=F-150

 

Went to my local pick and pull today and found a 00 F150 5.4L unfortunately it appears to only have two O2 sensor connectors on it. But I pulled the entire 9D930 sensor harness after testing it with my multimeter.

On this sensor harness it rings out correctly to each of the sensors. So I'm not sure exactly what the hell happened to my truck or how it got this messed up harness, but replacing it could fix the issues Im seeing. What I need to do next is trace +5v into the PCM and then trace +5v out of the PCM and see if the harness was dropping the voltage somewhere it didnt belong.

Perhaps this harness was attached because a different engine was put in the truck. I guess I'll have to do some extensive PCM pinout testing to make sure I'm not making a mistake.

Ill take the time to do a thorough cleaning of my engine bay too. So damn dirty in there.

 

More answers. My drivers side valve cover reads 8G894AA which translates to 97-98 Ford Expedition 5.4L. This answers so many questions.