Tach Help?

[Hubzy.]

I need some help figuring out why my tachometer is behaving this way.

I was doing it when I purchased it.

79 T/A, 403 Olds engine.

The previous owner didn't know why or when it started doing this.

Any help is greatly appreciated.

The tachometer stays at 4,400 rpm when the car is off. When I start it, it drops to around 3,000 rpm and stays there.

 

[Munkyslut]

A 403-powered ‘bird has pretty much the same wiring as the other engines, as they all use a generic GM HEI distributor.

Check the wire condition, crimps, snags, etc., and continuity from the tach wire to the distributor cap and the fuse box.

No need to check the fuse, as you obviously have power to the tach circuit board, or it would just stay at rest.

Poor connections & damaged wires are the main culprits for tach issues; otherwise, the tach itself is faulty & generally requires a new circuit board.

 

[Hubzy.]

A 403-powered ‘bird has pretty much the same wiring as the other engines, as they all use a generic GM HEI distributor.

Check the wire condition, crimps, snags, etc., and continuity from the tach wire to the distributor cap and the fuse box.

No need to check the fuse, as you obviously have power to the tach circuit board, or it would just stay at rest.

Poor connections & damaged wires are the main culprits for tach issues; otherwise, the tach itself is faulty & generally requires a new circuit board.

Okay, thank you.

I'll start digging into that.