In dash tach not reading correct when hooked up to msd 6al b

[lonewolf malibu]

Hey everyone. I installed rally gauges w tach into my car that was a sweep idiot light cluster.Everything works fine but the tach. I have the lead from the tach from the pin connector hooked up to the tach output of the msd 6al box. At a idle it seems to read fine. at 3000 rpm the tach reads 5000. The tach is out of a v 8 car. Called msd told me to install a tach adapter. I did w no change. then they said to run a diode inbetween the tach out put of the box and the tach adapt I did No change. Thinkin it might be the tach itself i swaped anothe stock v8 tach in. No change. Im at the end of my rope. Ne1 have some advice? Any help would be greatly appreciated. Thanks, Mike.

 

[liquidh8]

Re: In dash tach not reading correct when hooked up to msd 6

The MSD box it set-up for a v8 car right? And is the factory capacitor still hooked up to the factory tach? On the factory tach cars there is a little capacitor under the hood on the firewall, I think you are supposed to leave that in.

 

[ScotSea]

Re: In dash tach not reading correct when hooked up to msd 6

There is a resistor on the tach circuit board that just goes away with time. This resistor sets the gain for the tach circuit. If these resistors go bad, the tach starts reading high. If you search on the web, there are lots of articles that address how to fix the problem.

 

[liquidh8]

Re: In dash tach not reading correct when hooked up to msd 6

This guy says he tried 2 tachs, wonder if both are fubar?

 

[ScotSea]

Re: In dash tach not reading correct when hooked up to msd 6

I have several that I bought, not a one is correct.

 

[lonewolf malibu]

Re: In dash tach not reading correct when hooked up to msd 6

Yes the msd is set up for a v 8 car. And as u said the resistor on the fire wall is a tach filter. i have 1. Msd says disconnect it, Ive tryed it with and without it hooked up with no change. actually with the filter hooked up the tach doesnt work so msd was rite. As 4 2 bad tachs, nething is possible. And as for the forum on the resistor on the back of the circuit board of the tach, does ne1 have a link to that? Again ne help is appreciated. And thx for the replys guys. Mike

 

[malihoochie]

Re: In dash tach not reading correct when hooked up to msd 6

This one may help you out.

http://www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=646206#Post646206

 

[Doober]

Re: In dash tach not reading correct when hooked up to msd 6

A little late to the party... I had the same issue. I have a 2nd tach that reads even worse than the first one. I also used this one:
http://www.thirdgen.org/techboard/electronics/357893-90-92-tachometer-fix.html