Pierce Throttle up in pump gear failure
Here goes another one. Found a similar thread but not a lot of details. Here is our problem.
1999 Pierce pumper. It has a Detroit Diesel series 40 engine. A Navistar engine. Allison transmission Hale Qflo pump with a Class 1 governor.
Problem is that when the truck is put in pump gear it will not allow the governor to throttle up. It continues to allow the foot throttle in the cab to have control of the RPM.
The class 1 governor does have voltage output to increase the throttle but at this point the engine ignors it.
Had the regional pierce mechanic in for 4 hours plus travel pay and he found nothing. Told us to take it to the Navistar dealer for a new computer. Next at Navistar dealer we try a new engine computer and it made virtually no difference. They said they'd try to debug the throttle problem and after 3 weeks nothing. They said we needed a new body computer, the PMC (pierce micro controller) and it made virtually no difference.
Now several grand into this and we are basically no closer than when I first looked at it and found the governor putting out power.
One oddity they did find and make work is that the high idle in the cab works only in neutral with the park brake set. When active it does not set a high idle at a preset RPM but it does give control to the governor on the pump panel. To increase the idle the you have to go to the panel and increase it with the governor. Just seems strange and I don't remember how it worked before this.
Yes the transmission indicator does show drive when in pump gear. I think it reads 4-4? sound right?
Any idea what interlocks the engine requires? What each pin does on the engine ecm connector does?
Basically what does the Engine ECM need to accept the throttle control from the governor?? should the voltage be on pin 30 or 36??
We are at a loss and need this truck back in service.