"Bouncing" tach

[buddys06]

Today I was watching the tach at idle and it seems to bounce up and down about 100-150 rpm's is this normal?

 

[SLang]

No this is not normal. It sounds like you need to reset the gap between the Crank Position Sensor and the damper pulley. This need to be done with brass feeler guages.

 

[Ram4Sam]

Normal?

I don't know if it's normal but alot of newer trucks do it. Mine has done it since new but I don't want the dealer to manhandle my truck for something like this. One interesting note, after the MAP sensor took a dump on my truck last summer, my tach hasn't been near as bouncy with the new MAP sensor. Is there a connection, who knows.



SLang, is your idea a fix for this or a WAG?



Sam

 

[buddys06]

Thank's SLang for your reply. What other problems could this cause besides the erratic tach?

 

[Straight6Jeff]

My tach bounces at idle and while I have cruise control on. However, I do not see any speed variation when the tach bounces. Time to break out the manuals

 

[SLang]

This is not a WAG (at least for most trucks). After I had the front cover off of my 97 I had this problem. I did not have a set of brass feeler gauges handy so I "miked" a piece of cardboard to fing the correct gap and used it. I found my tach bounces a lot. So before taking it out of the garage I did the cardboard trick agian this time it bounced a little. Drove to the local NAPA and got a set of brass gauges for $3. Reset the sensor and no troubles since.



I have done this on a 95 after mudding and it worked and on a 01 after the dealer had troubles. The 01 did not completely stop but bounces small enough you con not see it unless you stare at it. 95 fixed completely.



You must use a non-magnetic material to set the sensor. If not you will magnitize it and possible ruin the sensor. With brass gauges and about 15 min. of your time it's worth a try.



Scott

 

[azcummins]

My 98. 5 24V has always done this from day #1 so I just figure it is the cummins wanting to go!



Doesn't bother me that much unless people think it could have a negative effect @ higher rpms.