So years ago I bought a Parts Place repro "in dash tach for my 72 Skylark. It worked great for years but upon start up and cranking the engine it would surge all the way up. It did this for years and then sometimes it would work and sometimes the tach wouldn't work. Now it doesn't work at all. Besides checking the wiring, any common issues with these tach and is there a way to bench test it? Car has a pentronix (I think that's what it's called). Electronic points conversion kit if that matters. Thanks
I will have to check but pretty sure it's just the one that replaced the points, you would never know unless you removed the cap. Will check tomorrow. Thanks
There are 3 different versions of Pertronix that replace the points. The coils are, I believe, all different. They should be "Flamethrower" I, II or III. This may give you a hint if you cant find it on the unit.
Hmmmm. So would having a stock coil be part of the problem? The tach didn't work at the time but a few months ago I had a wire connection break near the coil, when I tried to put it back on the cool connection stud just starting spinning so I went to Autozone and bought a stock coil. What am I looking for on the pentronix? (Numbers?)
I know the Pertronix coils have very low resistance. The Pertronix also requires 12 volts I believe. Don't think a stock coil can work with the full 12 volts or Pertronix system work with the resistance wire.
Everyone says pertronix requires 12v but that is patently false. The base pertronix kit is a points replacement. All it does is replace the points. Uses the stock resistance wire and factory coil. I've installed plenty and never had an issue
Coil won't be an issue. If its the Pertronix 3, it s a multi-spark. Our tachs cannot deal with multi-strike operation.
I would think that is the reason that MSD boxes have a separate tachometer connection on the box. Pertronix ignition drives the tach off the negative side of the coil, so yeah, I could see multiple sparks playing havoc with a stock tachometer. Scott, would your conversion mechanisms fare any better?
No, the electronics are not sophisticated enough to distinguish between a multiple spark event and high rpm single spark operation.
Ok, I am getting a little confused and I appreciate everyone's help. Here is a picture of what I believe to be a Pertronix points conversion in my '72 350. I had been using a stock coil for 3 or 4 years and the tach (Repo Parts Place) worked fine with only exception being that upon cranking cold engine, the needle would pin all the way up and maybe go back and forth a bit until it started. It got to the point where sometimes it would work and sometimes it would not and then one day it stopped altogether about a year ago, A few months ago I needed a new coil, installed an AutoZone factory style coil and Tach still doesn't work. I am coming to the conclusion that the Pertronix maybe caused the spike in the tach and ongoing issues. Are all the responses above suggesting that the tach shouldn't have worked at all with the Pertronix set up? Or is there a way to make it work? Or do I have to go back to points for the tach (once fixed) to work? thanks all!
I've installed the pertronix on the beater and the factory tach worked normally. On the aquamist car, I had a crane xri installed and that cars factory tach worked fine. Do you have another tach you could try by just wiring it up under the hood as a test?
That looks like a Pertronix 2 lobe sensing model. The Pertronix 3 looks a lot different than that, and it is the one with multiple sparks. I don't think the Pertronix, or the coil is at fault. It's probably the tachometer itself. Test it and find out. Try the tachometer on another engine.
