Pcm Failure

Adesokan Diagnostician Nigeria Posted   Latest  
Unsolved
Electrical
2004 Ford Expedition Eddie Bauer 4.6L (W) 4-spd (4R70W)
Crank / No Start

Good day! I was call from another shop to check on 2004 ford expedition, no start after engine replacement with junkyard engine. I diagnose it and find out that the pcm was bad. When i open the pcm i found out it as burn, pcm was replaced with used one and i checked for short before installation. After installation and programmed the vehicle start but unable to rev the engine and also dead misfire. I changed the pcm after few day off troubleshooting. i found out that the pcm was 5.4L instead of 4.6L. i got another pcm with 4.6L. After the installation as am about to program it i found out the pcm had burn out and the positive battery terminal was hot. Please, what do you think can caused this? Now had gotten another pcm from junkyard, but i want to figure the issue out before i install another pcm. Please, what is your suggestion on this fault?

Thank you in advance... 

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Nolan Technician
Bahamas
Nolan
 

Are you sure that PCM is a good one, sometimes it's the small things?

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Adesokan Diagnostician
Nigeria
Adesokan
   

I got it from the savage yard. Am confused, if the fault is from the pcm or the vehicle. Before installation i checked the wiring and was okay…

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Nolan Technician
Bahamas
Nolan
 

Did the burnt PCM blow any fusses if so I would start with those circuits?

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Adesokan Diagnostician
Nigeria
Adesokan
   

Am not sure of that i will check that today Thank you sir

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Glenn Owner/Technician
Texas
Glenn
 

Hello Adesokan, What was the reason for the original engine to be replaced? Sounds like the issue existed from the beginning. This thing is smoking PCM's and should not be. The best test is a pinout test at the PCM connector to determine where a grounded power wire exists. Use a pinout chart and follow what conditions and steps are needed. I also recommend checking the harness where the…

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Nolan Technician
Bahamas
Nolan
 

Hello Mister Hunt, not trying to go off-topic here but I have never heard about this output terminal test at the ECM connector for a shorted circuit, hopefully, later when time permits that could be covered a bit more thank you for your time.

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Glenn Owner/Technician
Texas
Glenn
 

Hi Nolan, Ford and other manufacturers actually have a test called a “pin out test”, Many techs avoid this until the very last step, after all other methods and guesses have failed. The test give a pin assignment number of the ECM/PCM connector and what the expected value should be when tested. Some tests are done with key on power and others are done with key off. In many cases, simply…

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Nolan Technician
Bahamas
Nolan
 

Thank you I will look that up on my information system, it sounds like a very positive test for wiring problems that mask themselves. I am learning something most interesting every day thanks for your time.

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Adesokan Diagnostician
Nigeria
Adesokan
 

The first pcm was also burn out, and i couldn't find anything wrong with the wire then before installation of the first one. I will check the wire harness and the pcm pine out today as you said

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Adesokan Diagnostician
Nigeria
Adesokan
 

Thank you very much sir I check that today

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Paul Owner/Technician
California
Paul
   

I'd guess that you'll eventually find a short to ground or low resistance on one of the outputs. I'd check all of the output terminals at the ECM connector and make sure they don't have a low resistance connection to ground or the output's “partner wire". I don't work on Ford at all, so I don't have any specific knowledge about what outputs might fail, or where the harness might get pinched…

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Adesokan Diagnostician
Nigeria
Adesokan
 

Thank you very much sir I will look to that

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Scott Owner/Technician
Missouri
Scott
 

Something that the PCM is controlling is pulling too many amps when turned on. You need to analyze the wiring diagram and test each circuit's resistance first and then if good, verify condition by measuring the amperage in the circuit. Do this by individually testing and/or jumping the circuits from the PCM connection. If the resistance is bad, then fix that before applying amperage. Amperage…

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Jason Owner/Technician
Virginia
Jason
   

I dont think it would be something the ecu is controlling simply for that fact of what in the ecu has blown out. The circuit damaged in the image is the main RUN supply. The exploded part below the filter cap is likely a blown zener diode. If it was an externally controlled device drawing too many amps then the damage would likely be at its controlling circuit. Its also hard to imagine the short…

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Scott Owner/Technician
Missouri
Scott
 

I didn't realize there was a picture until you posted this. Someone who knows the boards would likely know better than I.

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Adesokan Diagnostician
Nigeria
Adesokan
   

No, have not open good ecu yet because the ecu was not easy to open. So, it possible the problem is from the ecu itself?

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Glenn Owner/Technician
Texas
Glenn
 

Hello, Jason just brought up a good point. Check the under hood fuse box for an AC clutch diode that may have been reversed or substituted with a fuse. I seen this happen years ago on a Ford. Sometimes people get desperate and switch things around in fuse box while looking for magic fix.

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Manny Owner/Technician
California
Manny
 

Make sure your engine and body grounds are solid. Bad grounding may cause too much current flow through ECM and burn it.

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Jason Mechanic
New Mexico
Jason
 

I would look for a ground wire that might have been connected to the positive circuit accidentally. Possibly near the starter or even at the battery. Looks to me like power being introduced to a ground circuit.

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Phil Technician
Massachusetts
Phil
   

What is the year or preferably the VIN # of the used engine? Was the engine harness replaced along with the used engine. I'm thinking you have a mismatch of parts and the harness on the engine is not compatible with the PCM in the vehicle. Keep it simple. If the vehicle ran before but needed an engine for whatever reason. If it is suddenly blowing PCMs up now then check to make sure the swap was…

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Adesokan Diagnostician
Nigeria
Adesokan
 

The harness was not replace. Just the engine. I don't know the vin of the new engine Thank you sir

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