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MP8 ENGINE NO CRANK WITH KEY SWITCH

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ENGINE WILL NOT TURN OVER WITH THE KEY SWITCH NO POWER AT THE STARTER.

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Many things could cause this issue from blown fuse to bad ignition switch, bad vehicle ecu or engine ecu. You need to check all fuses- ones under center dash panel and inside left side kick panel. Check voltage at starter relay w/key in start position, should be 12+ volts. If less than or nothing check ignition switch, I have seen the crimped connectors on the back of the switch be loose causing a bad connection. 

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We have an over heat solenoid on our mp7's, idk if it comes on all. We've seen a no start condition caused by this

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On 1/23/2018 at 5:59 AM, OJ Avery said:

We have an over heat solenoid on our mp7's, idk if it comes on all. We've seen a no start condition caused by this

All Mack mp engine starters are controlled by the engine ecu. The eecu provides the ground circuit for the starter relay. The purpose for that is to protect the starter from overcranking/overheating. If the eecu sees excessive crank time it shuts off the ground circuit to the starter relay for a minimum of 30 seconds. 

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Mine did the same thing. Took it to Mack and they pulled the oil temp plug on the driver side of oil pan and cleaned the oil out of it an it started right up. They told me it was a ground problem from the oil and said I need a new oil temp sensor. They told me the grounds has something to do with the ECM to the starter. Sounds crazy but it fixed my problem. Wished I would’ve knew that before I replaced key switch, starter relay and starter. 

Edited by TimberJack

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checked the plug on pan had oil on it cleaned it still no crank. switched out engine ecm  still no crank switched out cab ecu still no crank can use some help.

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 I can use a bump switch to spin  the engine over but the truck will not start. no power at wires to starter from the key switch.

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10amp ignition fuse in center dash panel. F7 I think..... Ive seen these fuses blow when the polarity at the mag solenoid on the starter is reversed by mistake or the solenoid is fried.

Your dash will light up etc but on key turns the starter won't engage.  Check the ign fuse. These trucks usually don't use the starter over heat switch supplied on the starter but as said earlier, time out by ecm. If it won't engage at all this may be your issue. 

This simple issue surprised the heck out of me and only found it through using the Mack/Volvo online wiring diagrams.  

Stumbled on this issue after new starter was installed by customer.

Let me know if that helps.

Edited by bbigrig

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my old MP7 granite did the same thing years ago, had it towed back to Cambridge from Halton Hills, all because some 14 gauge "trigger wire" rubbed through on the trans. 

 

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I have a 2009 Mack with a mp-8 . 

You turn on the key and crank the starter will engaged for about a second or less then it shuts off you can cycle the key and it will do it again it has a new wire harness new starter all the fuses and relays have been replaced the dealership is worked on this problem  4 different times and have not fixed it my question is it possible that the engine ecm is bad or the eecm I don't want to replace the wrong one

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11 hours ago, George h said:

I have a 2009 Mack with a mp-8 . 

You turn on the key and crank the starter will engaged for about a second or less then it shuts off you can cycle the key and it will do it again it has a new wire harness new starter all the fuses and relays have been replaced the dealership is worked on this problem  4 different times and have not fixed it my question is it possible that the engine ecm is bad or the eecm I don't want to replace the wrong one

Sounds like the cam position and crank position sensor connectors are crossed. The ecu  see's excessive speed and shuts off the starter. 

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I have an 09 Mack with an MP-8 also.

Has anyone ever gotten the message 'operation failed' when checking for diagnostic codes?  Whenever I have checked for DTC codes in the past, if any were present, they have always came up with the proper code numbers.  I left the truck idling to load a machine on the trailer and got ready to leave and noticed the truck had shut down.  All of the electronics and A/C were still on but the engine had shut down and no alarms.  This truck does not do that like the newer ones do.  Turned the ignition switch off and back on to fire the truck back up, but the starter will not turn over.  The relay under the CB is clicking, the batteries have proper voltage and proper voltage at the starter but will not engage.  After this happened, I checked the DTC's and when I go to the 128 Engine code section the 'operation failed' keeps coming up.  The ABS, Cluster and VECU all come up with codes which all show up to be a J1939 data link connector.  The dealer says that this is the entire wiring harness.  My suspicion is the ECU has gone haywire since the engine code shows 'operation failed'.  Has anyone had this pop up on their codes?

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Usually it’s the engine ECM has died . See if you can read the engine hours in the display under trip data . If just dashes shows up and no numbers then there’s a good chance the ECM is fried. Hopefully is just a fuse though but be prepared for a ECM

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Brother, you hit the nail on the head!! Just checked the hour meter and nothing but dashes. All of the fuses in that lower left box check good for continuity.

I have been suspicious of the ecm going haywire for a couple of years now, but everyone says not likely. I had a brief spell on a trip a couple of years ago that the truck acted strange on the interstate and the lightning bolt and other lights came on. By the time I got off the interstate and checked under the hood, the lights were out when I got back in the truck. The truck has never had the same power since that incident and occasionally still flashes those warning lights briefly, but never stay on long enough to get it checked. The best that I can remember, the hour meter was showing around 5 or 6 thousand hours prior to the original incident. Ever since then, the hour meter jumped to 9,999 and has stayed there ever since.

THANK YOU for your help!!

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Can't win this one. Put a new ECM on the truck and the 4 DTC codes that were showing went away and the engine hour meter is back to reading correctly, but the truck still won't crank. It now has a code on the VECU saying that there is a grounded or broken wire. Anybody have any suggestions??

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I have mack 2009 mp8. It not starting. I change the starter and it start, but after about 5mins, it goes off and didn't start again. Since then I have been pushing it to start, but just rolling. When I just start it with 12+ from the battery it starting. But I tried to use the negating wire on the tyre reem and the positive on the battery it roll better. But still didn't start

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