7.3 PCM

family xj

Well-Known Member
Joined
Feb 19, 2006
Location
Jacksonville NC
Has anyone else had a problem with their 7.3 powerstroke killing their PCM?

My 01 Excursion with 215k miles had a PCM and IDM replaced when it was around 200k. Well this week the dealer has told me the PCM is bad again. Any ideas what would cause this? I did have a ICP sensor that was bad and a bad Back pressure sensor.

I have a hypertech programmer on it but I had it on 50K miles before the first PCM went bad.
 
What originally made the IDM go out? The wiring harness under the valve covers is defective in the 99-01 or 02 I believe. The connector retainer gets weak and the plug under the valve cover begins to seperate. When that happens, the injector voltage can arc against the block. the IDM makes better than a 100 volts DC so there is enough potential there to make the arc happen. Then the IDM can short out and also can make bad ground loops and possibly get the ECM.

Have you put the small plastic piece on the harness under the valve cover?
 
I haven't messed with it yet. I have read that it gets bad and causes problems. that sounds like a simple fix to me. I just hate to tear it all apart.
 
Oh Ya. There is so much info. I am pretty overwhelmed with this diesel stuff. I am worried now that the IDM is bad too. They told me today they were havin a hard time gettin the PCM to take the programming.
 
Do you have it at a dealer? Who is programming it? Whomever you have working on it, quiz them about their knowledge of the 7.3. People have spent a ton of money on their trucks that didn't need to be spent. I had a friend that was told he needed new injectors. When that is done, you have to get under the valve covers. The injectors are replaced, the harness plugged back in, and the truck runs fine. All along, it was the wiring harness.

Not even all dealers know about the ins and outs of the 7.3. It's better now that the 7.3 has been around so long, but do your homework and make sure your mechanic is familiar with them.

Good luck.
 
I went today to get the truck but its still not right. When I got there it didn't want to start. They said the battery and alternator were bad. Ok so the one battery was only hold 575 cranking amps out of 850. But the Alternator was surging up and down really bad. He showed me how it was surging with an OHM meter. When it surged the engine ran really really bad. So we assumed it was bad. Still under warranty I went back and replaced them both. When we bench tested the alternator they put a load on it and it about stopped the machine like it was locking up. Once replaced I went to start it and it wouldn't run at all. Maybe the new key I have is not programmed right. He has the other Key and was one when I got back. I am pretty frustrated though. He did explain how to test the harness under the valve cover with out taking it off. He showed me on one that they had just removed from another truck with a bad motor.
 
All that sounds pretty frustrating. I hope it all works out for you.
 
Well this morning I was there at 8. Got the Mechanic and we went out to the truck. He tried to start it too and found the same result. So we pulled the computer out and tested it. Got a code 1688 I think or something like that where the PCM and IDM weren't working together. So we decided to try the IDM he had on the shelf and see what happened. Well when we pulled the harness on the IDM water poured out. Definitely a reason for the IDM not workin and shorting out. Plugged his in and it fired up. So Off to the parts store I went. Not Ford since theirs cost like $800. Mine will be in at 730 so we will see what happens tomorrow. At least he hooked me up today and didn't charge me for diagnosing it more. He is hookin me up tomorrow too. He is trying to help me out as much as he can.
 
Still fighting with it. Got the IDM in and found a bad wiring connection. Ziptied up and brought it home. Ran good. GF took it to class and found several new codes relating to injectors on Passenger side. Found a lose bolt that holds connectors together. Tightened it up and it ran great. Drove home still no issues and all codes were gone. Went and picked up a Tahoe on my trailer and it was running great. Then tonite cruising around town it started acting up again. Limped it home and waited for the GF to show her and of course it ran fine while she was here.I think the Harness under the Passenger side valve cover may be bad now. We will keep trying to find the problem. I will keep updating
 
I started feeling the wires and got a slight zap from the harness near the Drivers side valve cover harness. I pulled back the plastic cover and tape to find 6 of the eight wires insulation deteriorated. So we made a temp fix to see if that was the problem and it wasn't. Definitely part of the problem. As I adjusted or moved the plug into the Valve cover harness it would run realy bad. onna pull valve cover and put in a new harness.
 
So we replaced the harness under the valve cover and that seems to have fixed the issue. The wiring harness fix outside of the Valve cover is working well. Trucks runs better than it has in years
 
Great! Those under valve cover harnesses suck! Many people have spent many dollars on other things when that was really the underlying problem.
 
Thought I would update. I haven't had any troubles since I got the wiring issues fixed. For my Borthday over the weekend my GF bought me a new Chip for my truck since my old prorammer wouldn't work. She got the power Hungry one that a lot of the Powerstroke guys are running. Its pretty awesome. 6 programs for under $400 shipped. I love the 140hp lope setting. I towed with a trailer empty to raleigh and got 12.1 mpg at 75 mph on the 65hp tow setting. Coming home with a blazer on it I got about 11.9 mpg. Running down the hwy on any setting I get about 17.1 mpg. Keep in mind my truck is lifted on 37's. Definitely one of the best Bday gifts ever. Did I mention she bought me a ARB locker for my XJ for no reason. Awesome GF. Definitely keeping this one forever
 
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