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w3grant

MP8 goes into limp mode

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I have a 2008 Mack with an MP8 in it. Trucks starts up and runs fine then while driving down the road goes into limp mode and wont go above 20mph. A previous mechanic scaned it and said it needed the oil sensor inside the pan they did that and we still have the same problem. That is why I am now looking at it unfortunately I do not have a scan tool so I cant read the data. Any help would be awesome Thanks again!

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Any warning lights?

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Could be a fuel issue also. If you have the stalk switch you can pull codes with it.

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Pop the connector (twist style) off the LHS of the oil pan, if oil made it through you'll be needing the updated oil sender/eop sensor and pigtails. Same goes for the eop, if it's letting oil pass through the sensor, it's fubar. I've done several of these and it requires a jumper harness to be installed between the sensors and engine harness.

Edited by Graves
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Could be air bag dump or power divider solinoid shorting out telling ECM that either is on and limiting road speed.

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Ok I will check the sensor in the pan. Where aboust is the eop sensor located?

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Right behind the ecm on the right side of the block. There are two but the top sensor is what you're after. You'll know it's bad if oil is making its way out.

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Thanks to all that helped I found the sensor that was leaking oil.Truck is back up and running.

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Make sure the interlock is not switched on, newer models have this feature enabled to only allow truck to run 15- 20 mph in the event that the switch is on.

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Posted (edited)

Have a 2011 Mack Granite with a mp8 engine. When I bought it the one wire on the small fuel filter was not connected but never a problem. Had it serviced today and the tech plugged the wire in and now I have a fault light. Will it go into limp mode?

Edited by Bill P

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If the regen switch is in the inhibit (down) position it will derate the engine also.

 

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