If the pedal is touched the rpms race up.After a while the engine will run normal until it goes uphill or at a quick start will smoke up.At 50 -55 it will not generally hold,instead it will fluctuate up and down quickly.Does anyone have a suggestion?

 

PMD?Boost sensor?

 

PMD or IP failing is the most common reason for those symptoms.

Flight systems PMD's often fail in that manner and can cause a runaway engine,any PMD not marked STANADYNE is a flight systems no matter what it is badge'd as.

 

Thank you for the quick reply.I am new at diesel engines,could you elaborate what a pmd or Ip is?

 

IP-injection pump

PMD-pump mounted driver or FSD-fuel solenoid driver,this is the black/grey box on the drivers side of the injection pump in stock form.

It is an electronic switchgear that amplifies ECM pulses to a usable current to run the IP fuel solenoid via transistors and other electronics.

They often fail and a common replacement option is to remotely locate it to a location outside the engine bay on an aluminum heatsink with an extension harness.
PMD's fail due to repeated heat cycling breaking internal solder joints that are not user servicable.

The best solution to date is to get them away from external heat sources and to shed the heat they generate when operating to the outside air so that they stay at or near ambient temps at all times.

Often a replacement PMD resistor is required at relocation time due to the difficulty of retrieving the original from the the IP mounted PMD.