PCM..now it works, now it doesn't, now it works... - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 8 (permalink) Old 10-01-2019, 04:50 PM Thread Starter
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PCM..now it works, now it doesn't, now it works...

2002 ford excursion 2wd 7.3 diesel

2 months ago random dying. had it towed to shop, they put on new fuel filters, new CPS. no change. after putting on new IDM, started right up. tested fine. have driven it for 2 months daily, no problems.

2 days ago was dead in driveway. will not start. has engine oil to proper level, wait to start light comes on, engine turns very strong, no fumes/smoke coming out of tailpipe. checked and replaced fuel filters just to make sure. no change. believed was likely the IDM again, borrowed one and hooked up. No change. still dead. many attempts before and after, would not start.

noticed last night RPMs not showing when cranking. tried to do live data scan to verify rpms, wondering if CPS went bad. reader would not connect to vehicle. buddy came over with his $5k snap-on reader, would not connect. tried unplugging/replugging, etc finally connected. vehicle started right up. my jaw dropped, since all my cranking never started it. restartedit about 3 times, then would not start again. repeat testing showed inconsistent failures to connect to computer each time would not start. when it would not connect to engine computer, we checked and were able to connect to other modules: ABS, Supplemental restraints, Security module, Instrument cluster. could not establish connection though to GEM and PCM though. tried checking codes for the ABS, Supplemental restraints, Security , Instrument cluster modules, but none showed codes. finally found a U1950 code from the drivers seat module. tried starting again, was able to run, could connect to the PCM, saw a code for ambient air temp (i oopsed and left the plug unplugged after working in that area unrelated issue ...power steering) and glow plug #7. #7 glow plug surprised me bc 2 months ago when at shop they also replaced the pigtail harness because connector pins were melted. after fixing it, they found the #2 pug was showing issues - weren't sure it was the actual plug or loose harness inside.

when we could connect to the PCM, i ran a buzz test and a glow plug test, and both came back fine. i will admit i am not really knowledgeable on those tests, have sen others say to do them, and they were listed in the snapon reader so figured i would check them since i had it in my hands.

thoughts please?
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post #2 of 8 (permalink) Old 10-01-2019, 05:28 PM
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Re: PCM..now it works, now it doesn't, now it works...

I haven't seen a controller come and go like that, I have seen bad grounds and/or power wires cause this. Normally when a controller goes it will show very random codes, even when you can finally get it to connect.

It does sound like a power and/or ground issue to me.
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post #3 of 8 (permalink) Old 10-01-2019, 06:06 PM Thread Starter
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Re: PCM..now it works, now it doesn't, now it works...

i dont have a lot of experience trouble shooting that...where do you start?
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post #4 of 8 (permalink) Old 10-01-2019, 06:48 PM
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Re: PCM..now it works, now it doesn't, now it works...

I would find a schematic and test power and grounds at the connector first. FYI some powers will be constant and some will be switched. I don't have a schematic handy for that but google may

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post #5 of 8 (permalink) Old 10-01-2019, 07:06 PM
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Re: PCM..now it works, now it doesn't, now it works...

I'm with Doc. I'd also check the back of the fuse panel for water leak from the windshield.
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post #6 of 8 (permalink) Old 10-02-2019, 12:56 PM
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Re: PCM..now it works, now it doesn't, now it works...

So its an 02 so, it has no gem. I say unplug the ebps and see of it will run and stay running. It could be something simple like the pcm relay.

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post #7 of 8 (permalink) Old 10-07-2019, 04:14 PM Thread Starter
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Re: PCM..now it works, now it doesn't, now it works...

still has random issues. i unplugged the epbs and it still will not start at times. so does this definitely exclude this?
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post #8 of 8 (permalink) Old 10-08-2019, 12:38 PM
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Re: PCM..now it works, now it doesn't, now it works...

Yes. Did you change the pcm relay.

01 f-250, Standard
Rev tech 4" lift, 37" military wrangler Mt tires
KC diy 66, Full force 160/100 and custom tunes from PHP
Banks intercooler and full 4" exhaust, Diy S&B intake
Diy quad feed, Hydra, Isspro boost, pyro, and fuel pressure
3/0 battery cables with military style terminals
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