Just a little info on my truck first, its a 24v Cummins with an auto tranny with 247k miles. a few days ago i noticed that every now and then when crusing my rmps will bounce pretty significantly. Enough that is audible. Anyone have any idea whats causing this. It only happens every now and then.

 

Mine did the same thing @ 35 to 40mph... its the voltage to the apps or tps.... mine was because my alternator was done for n the voltage was screwy.... new alternator n im good. Mine did it when it was really humid as well

 

Have a fuel pressure gauge? What's it showing when this occurs?

 

no i dont have a fuel pressure gauge. It usually happens at about 1500-2000 rpms

 

sounds like a crank sensor to me

 

Fuel pressure is crucial on these trucks, whether it's the problem or not, I recommend getting one, will save $$$ down the road