Jumping tachometer

I have a 96 taurus and my tach recently went from "Jumping erratically" to totally inop. Does anyone have any clues if one could troubleshoot what feeds the tach or anything that sends a signal to the tach? I don't want to just throw one in it and hope it cures the problem...just wondering if anyone else had had this happen. I did put a "new used" one in and got similar results. With the ignition off, the tack needle moves back down slowly to the stop, with the engine running, it goes back to the stop really fast...same with both tachs...which would tell me something is driving it down faster than normal with the engine running.....I was hopeing for a quick "Check that connection :banghead: or sensor" answer..we shall see....thanks Dave

Do you happen to have access to an oscilloscope? That would be the easy way tto test the tach as well as the tach signal to the PCM. The signal to the tachometer is provided via the PCM. The PCM will get the engine speed signal from the crankshaft position sensor (CKP).

I'd suggest you start by checking the signal to the tachmometer from the PCM. That line is could rule out the CKP and PCM very quickly. This will be a tan/yellow wire, terminal 48 at the PCM and terminal 8 at the instrument cluster. If you don't have an oscilloscope, you could probably get by with an AC voltmeter, checking for a steady voltage reading that changes with engine speed.


-Rod

The car doesn't happen to have a aftermarket remote start does it? If so then they'd have to go to the tach wire so that the remote start could monitor your engine. Most places that install these things don't do a very good job, so you could check over their wiring. Maybe it's a bad connection or the main unit is now bad and it's effecting your guage reading. Just something to think about if you have remote start :)