I have a MSD replacement coil and my tach is double what the engine is actually doing. I don't remember it doing this when I first put it in, well over 5 years ago. But since I haven't drivin the car in over 5 years I can't really be too sure what it did back then.

My question is how can a coil deliver two sparks per cycle without some sort of Multi Spar Computer Controller? I hear that some coils cause the tach to double because its fires twice. But I dont understand how just a coil can accomplish that on its own.

Also can a coil go bad from just sitting over time? The engine still seems to not run as smooth as it should, even after a Timing adjust (again how can a TPI enginelose it'stiming from just sitting?), and new Dist. Cap and Rotor.

It's a stock 1990 IROC 305 TPI

[IMG]local://upfiles/7917/57D9D83D970F497D912323FD0DEFF38B.gif[/IMG]

 

A coil does not deliver multiple spark. It would need another unit to co with it. Its just a coil made by MSD but has no mutiple spark discharge. For that you would need thier 6-a or 6-al. Those coils are just suposed to have improved windings and a better saturation so it does not lose power at high rpm.

 

Thats what I thought....any ideas why my tach is showing double then? I haven't been able to find a stock coil to throw in, but so many people keep telling me its my coil. Why would it be exactly double?

 

It may be the coil because that is where the tach pics up its signal. But the ignition also gets it signal from there also so it may not run correct and may be your problem. Or possibly the ignition module. You can have those check at autozone, maybe other places as well