Engine/Transmission (1998.5 - 2002) Tach. Bouncing.......

[onestackdram]

Last night the wife and I are out at the local dirt track, and when we went to leave we were sitting in the truck letting it warm up. And as we are sitting there two things catch my attention. Her tach bounces by about 50 or 75 RPM's at idle. Then second thing is that even though it was pretty chilly, it doesnt seem that her heater grid cycles, or does the 24v not have one? Or if it does, does it not pull the alt, as hard as they do on the 12v?





TIA



Russell

 

[01smokinram]

Tach

The tach bouncing like that is normal. It may have not been cold enough for the grid heaters to come on.

 

[onestackdram]

Thank you, I wasnt so much worried about it, I had just never seen that in a diesel before, so I was curious. And as far as the grid heater I kinda figured that it might not have been cold enough for it, but again I wanted to ask.



I do have another question though. What is the best way to tell if the her truck is warm enough to take off? Simply by water temp?



TIA



Russell

 

[01smokinram]

Usually i let mine warm up for 5 minutes and then take it easy till the temp gauge starts moving.

 

[NShadbolt]

I know someone that is a cummins mechanic and I asked him about the bouncing tach and he said that there is a sensor on the flywheel housing and that it might be dirty. I have not looked yet but it might be a simple solution.

 

[RustyJC]

My tach has bounced 25-50 RPM or so since day 1. Hasn't gotten any worse or any better over the past 1. 5 years. Nature of the beast, I guess. (Remember, these tachs take a digital signal from the PCM and display it, so if the PCM is rounding, let's assume, to the nearest 25 RPM and the truck is idling at, for instance, 662 to 663 RPM, the tach would bounce between 650 and 675 RPM. )



Rusty

 

[WestTN]

warm enough to take off?

I just start mine and leave. I did the same with the old one and it still runs like new with 270,000 miles. Warm up is a waste of time and fuel and it irritates your engine. they hardly warm up until loaded anyway.

My $. 02