kt22magic

Over the weekend my roommate and I installed a new Hypertech power coil and MSD 8.5 mm plug wires on my '89 coupe as well as a new glass targa top. Everything seems to have went well except for the reading on my tach.

It will read properly up to 3400 to 3600 rpm and then goes haywire any rpm above that range. This is very important for me because I have a ZF 6 speed and I need to know when I max out the torque curve (4500 rpm) and not bounce it off the rev limiter. I know that it's possible to do with out a tach but I like to have it for reference.

Has anyone else installed a power coil and plug wires and experienced this issue? Any help is appreciated, as always.

Thanks,
Kevin

DanielRicany

Yes this usually happens with any aftermarket coil. I used an MSD and sent it back because of this. I now have a D.U.I. coil and the only reason why it works is because I also have an MSD 6AL2 which has a special tach filter built into it that allows it to work. I had to remove my OEM tach filter when I installed the MSD 6AL2. I also have MSD 8.5mm Super Conductor ignition wires. So you can either get an MSD ignition box or send the coil back. To be honest the factory ignition system is more than sufficient for even decently modified motors.

kt22magic

Thank you for the prompt reply, but I was afraid that was the case. If I had only known before hand I may not have thrown away the old coil.

How difficult is it to set up the MSD 6AL2 that you mentioned? And do you know if it will work with the currently installed Hypertech power coil and digital dash in my '89?

DanielRicany

I do not know for sure if it will work properly with a Hypertech, but it will work properly with a D.U.I. coil. I think the D.U.I. coil puts out somewhere around 50,000 volts.

The MSD ignition box is very easy to set up. Just follow the instructions on the packet for 5 and 7 pin H.E.I. Distributors.

kt22magic

Awesome, I'm glad to hear that. I'll have to give that a try with my hypertech coil and see how it works. Thanks again for the valuable information

DanielRicany

You're welcome.

383vett

You might want to hold on for a minute. I am using an MSD 6AL unit and my stock tach gets it's signal from the HEI distributor and the stock tach filter and has no problem reaching my 6600 rpm shift point. I use the tach output on the MSD for a shift light and a 2 step rev limiter.

C409

..... There should have been a metal grounding strap on the OEM coil that goes from one corner of the coil to the harness plug connector on the distributor cap ... the three wire connector ... this needs to remain in place with the new coil or , at the very least , the new coil should have a grounding wire for this position ... also check the carbon button for the rotor to make sure its installed correctly and has not begun arcing .......

DanielRicany

My stock tach is also hooked up to the distributor tach feed. But it may be the way the MSD controls the coil or something. I am not using a filter at all for my stock tach. I also have another tach hooked up to my tach feed from the MSD.

kt22magic

So you have two tachs total? And with the MSD ignition controller they consistently have the same reading both on the digital dash and the separate tach?

DanielRicany

Yes. But I have a Sun Pro Super Tach II as my aftermarket tach. It's supposed to use the tach adapter 8910 to work with the MSD ignition box for Sun Pro's, but mine works until the tach gets hot. When the tach gets hot it starts reading too much RPMs. Takes about an hour of driving for it to get to that point though. Haven't yet bought the adapter for it yet.

DanielRicany

I should clarify, when the Sun Pro gets hot and reads inaccurate, the stock tach still reads accurate.

kt22magic

Thank you for the clarification. I'll have to give the MSD 6AL2 a try with and without the stock tach filter and see what happens. The ideas are much appreciated