i have a 96 2.7 auto. when going hwy speeds the needle fluctuates wildly. it seems ok at slower speeds. what would cause this?

 

When the tachometer is acting crazy, is the engine actually running at normal rpm?

 

engine feels even. the tach swings from 2000-3500 constantly. when I stop or go much slower it behaves normally. I was wondering if it some kind of sensor going out on the tranny.

 

The tach gets the "signal" from the ICM...at least in the 4 cyl 5th gen, the 6 cyl might be different.

If the engine is even and it is just the tach...there might be something with the wires or the drive circuit.

What do you know about the history of this car?

 

The V6 is different. The tach gets it's engine speed output signal from the coil.

 

Difficult to test for, so you rule out everything else (like flaky wiring connections) then replace the coil. I'll try to find an old thread about that.

 

one new development...i drove it today but it was dry out, no problems. it was raining when it was acting up. i need to chk the connection. The car is a salvage title so it was in a wreck before i got it.

 

I'd be looking for flaky wiring connections, anywhere. Maybe RedBull has enough drawings to point out the ground connections that are related to the tach circuit. Ground points are suspicious for corrosion.

I don't know where G404 is physically located, but also check the tach-signal wires coming off the coil. If the collision was anywhere near the interior fusebox, there might be loose connections there.

Gonna be a tedious job to check all that.

 

Here's the location of ground G404. It is behind the front console (center area).

 

The clue about the wet weather leads me to believe the coil is starting to short out.
Use a spray bottle to mist around the plug wires and coil area, then run the car and look for little arcs.