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tbone1983

Mack MP8 Randomly turns off

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Have a 2008 mack mp8 that will randomly turn off.  Sometimes it will restart other times not.  On the last time it would not restart the dash cluster would turn on but the hour meter would just have dashes.  When I tried to retrieve the codes in the dash there were just dashes.  Like it was not registering the ECM.  The lightning bolt was on and the truck would not crank.  It was like the computer would not send the signal to tell it to crank.  Started it today fired right up.  Ran it for a bit than it shuddered and turned off.  Restarted with no issues. 

 

It has an intermittent VGT turbo code.  And the turbo will not spool while sitting idling.  We replaced the actuator and it seemed to fix it for a few weeks but now it is back.  I'm leaning towards a sticking turbo but in VCADS there is no excessive force on the turbo actuator and it reads normal.  When it is acting like this it will not regen.  I have a replacement turbo for it but I'm more worried about the computer.  When it tries to cycle the vanes while idling it will start to miss then clear up when it is not trying to adj the vanes.  Lightning bolt off and on during this.

 

Has anyone had one randomly turn off and occasionally not restart?  Any place I should be looking before we replace the computer? 

 

We have 4 of these gu's and have nothing but emission problems with them but the older RD's just keep going.  Unfortunately no one wants to drive the older trucks....  I'm a little desperate for some help on this one because I have another that is going to have to come in for an EGR issue this week. 

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I forgot to mention the truck would also randomly high idle.  Like max out 2k rpm. Only way to get it to stop was to tirn it off.  I thought this was strange also.  I have a feeling it is all related to the computer or some emission related non sense. 

 

I could really use some good input.

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I had a motorcycle that would randomly shut off... wound up being a wire going bad on the ignition switch. Possibilities are endless, but maybe one of the techy gurus will be able to make sense of it.

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Ya this is a tough one without laying hands on it. Sounds like ecu is losing power. Do you have a diagram?

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Posted (edited)

Freightliner I drive in the winter does the high idle (not 2k rpm though) sometimes if it's not plugged in. Part of the cycle to warm up the engine. 

Could be voltage fluctuations. Have you tested every cell of every battery? Could have a couple bad cells, dirty voltage can do crazy stuff to computers.... ECUs rely on varying voltages from sensors to determine what's going on. Bad batteries can give off irregular voltages yielding one confused ECU.

Caps can be popped off every battery, including "maintenance free" ones. Each cell needs to be nearly full of DISTILLED water, and with a simple float tester from an autoparts store you should have 4 of the 5 balls floating in a sample drawn from each cell. If you have a cell that's low on water or gives a low float ball test then chuck it and replace the battery.

Edited by JoeH

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Each ball implies 25% charge, so 5 balls would be overcharged.

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Does anyone have a wiring diagram?  I am looking for the pinout for the ecm also.  Is there a wire from the battery with a fuse that powers just the ecm like a cat?

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I sent you a message about a wiring diagram. Hopefully it will show what you need . 

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