I have a 91 RS and for the past few months it has been sitting.I drive it every so often but it sat for about three weeks before I could drive it again. My problem is the tach goes red line in normal driving and it gets buried when i step on the gas. If anyone can help I could use it. This does not give me any codes or effect the performance, it just bugs me out if I want to drive.

 

sounds silly, but i'm guessing the needle has done a 180 on you and you might try pulling the face off, and flipping it back down.
sometimes under extreme acceleration...or when in park/neutral and gassed HARD, the armature of the needle could flip and now it's happy 180 out...

 

I dont know if that is the prob. When I am sitting at a light the idle is normal, then as I step on the gas it goes up normal then it jumps up higher.What I would like to know if the tach is elextrical or if at any point it is vacum and there could be a prob. Also I have seen some other people talking about a "tach filter"? would this be my prob????

 

The tach is completely electrical, and there were no tach filters used in '91. Sounds like the tach itself has a problem. Check the connection & condition of the white wire that goes to the harness from the coil - it routes to the tach input.

Tim

 

One more question - if your RS has a V6, what are the yellow & red lines on the tach?

Tim

 

I have a 305 V8. I dont know what those wire go to. I will check the connection and the wires, thanks foe the suggestion.

 

Here's my 2 cents on this. You could have another electrical problem, causing your tach needle to bounce around. My aftermarket tach in my S15 truck was bouncing around alot, intermitantly. I thought maybe I had a miss in the engine under light acceleration. I found out that I had a bad plug wire. I think it came loose from the plug, then started arcing/coroding in the boot. Since the tach pickup is connected to the coil primary, the arcing was reflected back from the secondary(plug wire). I replaced the wire and problem solved.

Just thought I would pass this along.

------------------
Best ET 14.413 @95.57 without
pulling valve covers or manifolds.
Also with stock 2.77 rear end!!!

 

Thanks to all for your help. The problem was with the servo that controls the tach gauge. It had gone bad so I replaced it with a another and problem solved.