several years ago my tach started dropping to zero and after the dealer fixed it I had a rough idle that came and went. I blamed it on everything I could thin of replacing almost everything but the truck without ever fixing the problem. since then I have had many more errors saying low input voltage from the crankshaft position sensor and the tach would intermittently drop to zero. replacing the sensor seems to fix it for a few months but then it reappears. it seems that high RPMs make it act up and unhooking the batterys sometimes fixes it. since I doubt that 3 CPS sensors could be bad and I have had a new ECM computer put on a while back I am starting to wonder what could be doing this. any thoughts or suggestions?

Oddly enough I had just ignored the problem but whenever the check engine light comes on from the CPS low voltage my lift pump won't prime the fuel system so it can be a little harder to start. Works fine while the truck is running but when you first turn the ignition on prior to starting the lift pump doesn't run for a second like it does when I clear the code. lol That fact has baffled several people I have talked to about this.

Keith

 

hmmm my crankshaft position sensor change fixed that for good,im going to watch this post...

 

Well I guess at this point I will crawl under the truck this weekend while it is running and wiggle the plug and wires on the CPS sensor and see if I can cause it to act up.

Keith

 

My crankshaft position sensor wiring looks good and since this problem has been intermittent through 4 sensors I am starting to think the problem is the tone wheel. The fact that the problem hasn't gotten better or worse for so many miles/years leads me to think it must be mechanical.

Thanks,
Keith