M977a2 throttle issues. Need help!!

[jraney]

Working on a M977a2. Engine is running and sounds great. With transmission in neutral the engine throttles up and down fine. Once you place the transmission in gear you can no longer throttle. Once we put the transfer case in neutral then you can shift the transmission through all gears and the throttle works just fine but you cannot move with transfer in neutral. Place the transfer in low or high you no longer can throttle. The engine also reacts as if it has an over bearing load on it and lugs with black smoke exiting the exhaust. There are lots of sensors and electrical on this truck. Just curious of where to start? Any assistance would be greatly appreciated.

 

[NDT]

Are any PTOs engaged inadvertently?

 

[jraney]

Not to my knowledge. When we engage the pto you can hear it kick in when you disengage you can hear it shut off.

 

[Floridianson]

Just spit balling could the Trans. lock up solenoid be staying engaging when you go into high or low and releasing the button be pulling down the motor?

 

[jraney]

Very well could be. I a new to these trucks. Any idea where that would be located?

 

[jraney]

The vehicle will move forward in idle. Only thing is it does not accelerate when you press the pedal.

 

[Floridianson]

Been a long time but one of my 939 series the wire going up through the high low leaver to the button was a ground wire. Yes I checked it for being a ground wire and if it could ground out then it would engage the solenoid when we do not want it to. Have read some say the same wire is positive but mine was ground and if positive and grounding out would cause a short and we do not want that happing to.

 

[NDT]

This sounds like a WTEC transmission problem not a DDEC IV engine control problem. Pull codes on the transmission.

 

[jraney]

The ecm is the issue.

 

[Floridianson]

Looks like I need to brush up on my series numbers! Never was any good at them to begin with and Google is my friend for now.