randomly running rough, check engine on when happens. - Ford Powerstroke Diesel Forum
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Old 08-02-2011, 01:46 PM
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randomly running rough, check engine on when happens.

hoping to get some help here.

i have a 96 f450 7.3 auto service body with 115k miles. last day or so it has started to randomly run like a model T (best i can explain it). when this happens the check engine light comes on, then just as quick as it came on it might go off and run fine.

i have played with the 4 plug connections on the valve covers. my problem is much like it sounds with one of the plugs undone. my mechanic is convinced that the plugs are the problem, but to me it doesnt seem to change things by wiggling them when it does run rough.

also, the check engine light does not come on when one of the plug connections are removed, but does run rough.

so whats really bothering me is why the plug connections would be the problem if the check engine light doesnt come on when they are removed. when my problem starts, the check engine light immediately comes on.

sorry for the book, just wanted to be clear as i could. any help would be greatly appreciated.
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Old 08-02-2011, 08:28 PM
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bump..

i think he will be tinkering with the plugs in the morning while i'm at another job, i'll try to give him a hand after lunch. so i guess we'll figure it out eventually.. just hoping to get some extra help here. thanks.
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Old 08-03-2011, 01:05 AM
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Have you gotten the code pulled? So does it change at all when unplugging the valve cover harnesses?
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Old 08-03-2011, 04:06 AM
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Early year 7.3's use 2 connectors on each valve cover. Each connector feeds to 2 injectors and 2 glow plugs. What will happen on these is the glow plug connections will burn up, causing issues with whichever injector wiring it's near.

If you check codes it will tell you if this is your issue. Another thing to do is pull all the valve cover connectors and inspect them for melting. Usually it's obvious from the outside, but sometimes they will burn up under the valve covers and you won't see it without pulling them off.

If it melted bad enough it will sometimes melt the engine wiring harness. Ford sells a wiring connector that you can splice in to repair this.

If you do find melted wiring harnesses I would recommend replacing the valve cover gaskets, and both jumpers under the valve cover.
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Old 08-03-2011, 05:02 AM
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dude tried it this morning several times at advance auto... "no codes found".

bout right. I just had it fixed up and painted, no more than pulled it out of paint and body and it started this crap. of course they "didn't touch anything". when it happens, it runs like it does with one of the valve cover plugs undone. but check engine doesn't come on when it is undone.. if it happens to, it runs reeeaally rough.
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Old 08-03-2011, 05:31 AM
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Hmm, well it's probably logged it as an IDM code then. You need a scan tool capable of doing a KOEO (key on engine off) test and a buzz test. These trucks are weird in that IDM codes are logged and stored differently then PCM codes. In order to retrieve IDM codes you have to do a KOEO. In order to clear stored IDM codes, you need to first run the KOEO test, followed by the injector buzz test, then clear codes, This is the only way to clear IDM codes.
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Old 05-03-2012, 02:05 PM
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I know this is a old post but just wanted to see what the problem ended up being. My truck is doing the same thing. I already replaced the valve cover harness and replaced a burnt pigtail. Still I get the check engine light and runs rough randomly, and clears up and light goes off. Used my Edge programmer to check codes but found nothing, not sure if it checks the IDM codes though? It never stalls, it always seems to work itself out, sometimes takes a few miles and has no power at all. I did notice that if I let off the accelerator and downshift like when engine braking it seems to clear up faster. I am betting on the IPR. But the fact it never stalls make me second guess unless its sticking open rather than closed? Not sure, Thanks,
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Old 05-03-2012, 04:55 PM
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Did you check the other UVCH?
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Old 05-03-2012, 05:52 PM
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Sure did, actually installed new UVCH on both sides along with valve cover gaskets and replaced 2 of the pigtails that had some mild damage. With the truck running I can unplug the valve cover harness and as expected the truck runs rough, but the check engine light doesnt come on. When the truck does the random thing the light comes on and goes back off when the truck starts to run good again.
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Old 05-03-2012, 05:54 PM
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From my testing, nither the valve cover harness or the UVCH makes the check engine light come on in my truck, not sure about the newer ones.

Last edited by 95dump; 05-04-2012 at 12:17 PM.
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