Okay, my 98.5 24v Cummins 5 speed is doing a weird thing, haven’t driven the truck at all since I bought it as it was a project. Today it went legal, drove it around at when at operating temp at idle like a stop sign or light the gauge drops to zero, take off and drive again the gauge goes to 60 and stays there at any rpm and any speed. Faulty sensor or bigger problem, figure if it’s leaking oil from the vacuum pump it’s got oil pressure would I be wrong on that?

 

Well, I wouldn't think it's the pump. Probably the sending unit to the gauge. Can you hook up a mechanical gauge just to prove it?

 

Are you leaking any oil? It could be worn oil pump or restricted pick up tube to the pump. It's possible you have worn bearing inside but check the easier, cheaper things first. I'm not a diesel mechanic but on gassers I'll often put a high volume oil pump (not a high PRESSURE pump) to compensate for worn bearings. I'd check for leaks or a faulty sending unit first though.

 

My bet would be the sending unit. If you can just BARELY give it a bit of pedal, (while still on the brake) and pressure immediately comes back up, replace the pressure sensor.

 

Thats exactly what happens! Thank god