Tac Movement

[AgTires4295]

Wondering if my CPS is acting up... No problems on start, run, shutdown. Everything is working seemingly as it should although the other day I noticed my RPMs jumping on the tach when cranking.

Note: This was on a cold start. The truck had not run in a week.

[AgTires4295]

Went out, started it after sitting for another 6 days and the tach jumped around under 1k RPMs. Nothing abnormal in my 3 hour drive. Started it again and no tach movement on cranking. Any ideas?

[AgTires4295]

[NoRalPh]

I'm not sure I understand though,,,

You're not having a problem of any kind, you've just become aware of the intermittent movement of the Tach needle when cranking? - right?

You've heard "If it ain't broke, don't fix it?"

Here's the thing, with an '01, if you have a Trans Temp Gauge in the Cluster it means you have the electrical revision that no longer has the CPS directly drive the Tach. If you don't, then you have the earlier electrics where the CPS does drive the Tach, and give you some indication of the CPS's function. BUT, if the CPS wasn't functioning (and the lack of movement was indicating that) there's No Way it would start! The PCM would actually be seeing "0" rpm and wouldn't fire the injectors.

The more typical CPS failure has to do with Temperature. As the engine gets hot, the CPS fails to send it's signal to the PCM, the engine stops and letting 15-20mins go by cools it enough to allow you to restart again.

I don't think you have a problem....

[AgTires4295]

You've heard "If it ain't broke, don't fix it?"

Yup and thats the mentality Ive been reserving towards it.

The cluster doesnt have a trans temp guage so I am wheeling around the earlier electronics.

Thanks for the response.