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Rough Idle, No power, No OBD-II link.

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Rough Idle, No power, No OBD-II link.

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Old 05-22-2018, 03:29 PM
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Rough Idle, No power, No OBD-II link.

Working on my fathers 1995 F-350 7.3L. It intermittently has no power, goes into limp mode, and turns the CEL on. I cannot pull the codes out of the ECM with my bluetooth scanner and torque. I've even tried an expensive snap-on machine and cannot pull codes out of it. The truck sat for a few years, and recently we got it back running with a new FICM and some more replacement parts that I can't think of off the top of my head. I know for sure the FICM was replaced, CPS was replaced. I cannot get it to cough up the codes as to why the check engine light is on. I can't get it to maintain a stable link between the scan-tool and the ECM.

When the truck runs, it runs fine. However it will drop itself into limp mode and runs like garbage. I'm beginning to suspect that due to old age that the computer may be on it's way out. Is there anything I can check to confirm this before I go hunting a new one? Any ideas are welcome, and I'm at a loss here as to what to try next.
 
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Old 05-22-2018, 05:27 PM
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If your CEL light is on you have codes, the reason you cannot communicate with the PCM is because your PCm is pre OBD2 and has to get flashed for it to work properly with some scanners, the dealer and some Snap On scaner can read our trucks.check your UVCH and see of they aint got burned or loose connectors.
 
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Old 05-22-2018, 05:36 PM
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Thing is, I've had both the bluetooth obd tool and the snap-on pull codes at random. Right now I can get nothing out of it at all. Both pieces of equipment fail to link with the PCM at the moment. Should've included this in the first post but was typing it it out before I headed to work. I also suspected that the intermittent random running conditions might be the UVCH related. I've already replaced one of the pigtails for the UVCH before, due to a melted glow-plug pin. I do need to yank the VC's off of it and look at those harnesses too.

The intermittent no-link from the OBD/PCM is what got me thinking about that. But you do raise a good point with the UVCH possibly being a culprit.
 
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Old 05-22-2018, 06:16 PM
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Might want to check the #16 fuse in the cabin fuse panel as it protects the data link and the cigar lighter. If the fuse is good, make sure the contacts in the fuse panel are grabbing the spades of the fuse.
 
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Old 05-25-2018, 10:29 AM
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Originally Posted by farmert View Post
Might want to check the #16 fuse in the cabin fuse panel as it protects the data link and the cigar lighter. If the fuse is good, make sure the contacts in the fuse panel are grabbing the spades of the fuse.
I've pulled and swapped the #16 fuse already. Cleaned the contacts in the fuse box as they looked a bit corroded, and etc. Still getting an intermittent data link from this thing. Still can't get codes out of it with either scan tool. I'm at a loss for what else it might be save for wiring somewhere?
 
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Old 05-25-2018, 01:46 PM
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swap PCM relay with one beside it

also check this wiring out with ohm meter

 
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