Engine/Transmission (1998.5 - 2002) tach bounces at idle in gear

[Dheadington]

My tach bounces when in gear at idle with OEM injectors or DD II. When I put in park or neutral it is steady as it should be. Please help with any suggestions where to start looking.

Denny

 

[JCyrbok]

mine does too. Has since the day I drove off the dealer lot. It maybe varies 150-200rpm while idleing in gear. The way I understand it is that this is normal as the ECM is constantly updating and adjusting various engine parameters, suchas timing and that it actually can do this so quickly that it can happen several times on one cylinder's cycle, thus causing the bounce. (If im off on this some one please chime in)



If its more than that much of a variation it may be the trans. I had a 97 1500 and when the trans started to act up there was kind of a "surging" that whould happen while I was stopped at a light. Tach would rythmically drop about 500rpm then back up to normal. I forget what caused this though.



Hope this helps.

J-



BTW does it do it with the EZ on too. Is it better or worse with it on? Maybe its going bad. Has it done this always or did it just start?

 

[Dheadington]

tach bounces

I have removed EZ still does it. It seems worse now than it did new still only 100-150 RPM bounce. I added engine upgrades back and no different from stock to upgrades.



Denny

 

[JCockrell]

Tigger Tach

I had this same thing happen, I replaced the crankshaft position sensor. Took care of the bouncing tach. Got the sensor from Cummins. I don't remember part # or cost. I could probably find the paperwork when I get home.