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Mystery 2015 GU electrical problem


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I must be cursed with mystery problems!

I'm working on a GU with an MP7 that will occasionally either die and not restart, or just won't start at all.......UNTIL you unplug the engine ECU. Then it will fire right up and might run trouble free for 3 days until it happens again.

When the problem occurs, I have no communication with the engine e cu. No coolant temp, oil pressure etc. No matter what I do, it won't start until I remove power from the ecu.

I have replaced the ecu, but that didn't fix it. Sometimes when you turn the key on, the ecu will communicate fine, but as soon as you hit the starter, it will clunk and then the engine ecu goes dead. Other times, it's just dead from key on.

I've tightened and cleaned every cable on this thing. Frustrating!

Any ideas?

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I would look very close at the ECU and VECU connectors and pins for corrosion, loose in the connector housing where the pin pushes back a bit when plugged in or bent / miss aligned pins. Check the harness it self for worn or rubbed places

Edited by 41chevy


 “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’


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Check the fuse panel by the clutch pedal for water damage. Pull one of the bottom relays out and look for while crusty corrosion. There was a recall for this on some units . Follow the battery cables all the way to the starter . Look for them rubbing the frame rail or transmission. Check the ground lug welded to the frame behind the battery box. Is there any GPS/data logger/Qualcomm hooked into the diagnostic connector? We had a faulty Qualcomm cause lots of issues till we unhooked it . Check the terminal strip by the fuse box on top of the dash , there are a few ignition, battery and ground connections there , also 2 data link terminals, make sure nothing is touching them . We had a guy hook a CB up and his power wire terminal twisted over and touched the data link terminal causing a problem that took a day to figure out .  

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Thanks guys I'll check those out. My fear is that I'm going to kill power to it which will bring it to life again for another 3 days and not be sure I've fixed the problem. 

These are the jobs that I wished I still worked at a dealership. If it wasn't fixed after tossing a couple thousand bucks at it, oh well! Can't do that at this shop though.

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