Kinda stumped

ggoodson90

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Sorry for the long post but I'm kind of stumped right now.

1995 7.3 powerstroke, all stock except for downpipe and 4" exhaust and intake. Truck has always ran great other day my tachometer stopped working, truck sill ran an drove like normal, was able to read rpms off torque pro...anyways I was looking for any loose wiring or blown fuse that possibly could have blown an cause tach to stop working ( I know it works off pcm) just checkinf, well I didn't know what the plastic looking fuse was under the hood fuse was, I thought it was just a dummy fuse or something, so I pulled it while truck was running, truck died, I plugged it back in an truck started back up an ran really rough, like only on one bank of injectors check engine light came on, hooked up my old super chips tuner to scan and nothing came up, then check engine light went off on its own an truck idled/ran normal, took it for a drive today, drove it 30 miles one way was 0 issues all normal minus the tach not working, then on the way home truck did the running rough with phantom code check engine light again, running super rough no power, soon as I let out of the throttle check engine light goes away. Truck runs fine again for a couple miles then does it again and continue to do it basically on the 30 mile trip home. So is it possible I unplugged and hurt the diode in the fuse panel under the hood? Is it possible I hurt the PCM or damaged it doing that? Truck ran perfect before this.

Update, had it running today before I pulled pcm and idm, I unplugged the pass side valve cover connectors and it sounded exactly like how it was running when the CEL light comes on. I checked it while it was unplugged an running NO CEL,and no codes on scanner. Kinda leads me to believe the idm or pcm is having a problem, and when it's having a problem with everything plugged in its recognizing a fault an throwing the CEL,Gonna send them off to Chattanooga diesel to have them tested.
TIA
 

Tiha

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Never hurts to send them off and have them tested. I would guess you have 2 problems. The tach not working might just be the tach in the cluster.

The running issues, could be heat related to IDM, or could be valve cover harness.
 

ggoodson90

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I agree, the tach is most likely just cluster failure, not a huge issue there. I'm thinking it's gonna be the idm personally, if they test good, I'm gonna go ahead and replace the valve covers gaskets and harness and glow plugs.
 

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