1986 Chevy El Camino tachometer

Are you referring to the factory tach? There is a terminal under the HEI distributor cap for the tach terminal. It's next to the 12 volt power terminal.

Caradiodoc

OH! I stand corrected. To my knowledge, there are only six or eight pulses per two crankshaft revolutions on that tach terminal so the calculation would have to be done by the tach. Knowing what the pickup assembly looks like, there is no provision on it to provide only one pulse per camshaft revolution. That would say the tach is now receiving 8 pulses when it expexts to see only 6.

If I'm right, you will have to scratch off the numbers on the face of the tach and paint new ones in the right places! OR, ... There could be a switch to set or a plug-in circuit board to replace.

I have calls in to two experts. I'll post an update when I get a reply from them.

Caradiodoc

I haven't been able to come up with a definite answer, but I do have some suggestions. First, remove the tach and look on the back for an adjustment control or switch. It could be behind a small hole in a metal rear cover.

There could be a plug-in circuit board on the back of the cluster. Look on that for a switch or adjustment.

A number of years ago I was asked to repair a factory tach from a 1970 Plymouth Superbird. I needed a schematic diagram, and the only way to get one was to draw it up myself. The circuit board only had 20 parts. It was a very simple circuit and it ended up having a wire that could be moved to a different location for different engines.

Other than those things, I haven't heard from anyone who said there are different tachs for different engines.

Caradiodoc