Ive read some cool stuff on pelican about adding a resistor etc,to modify your tach.No specifics for my situation though.My tach is pulsing 2x's as many times as it should for my setup.That is,when it reads 5000 rpm,its actually running 2500 rpm.(deduced from reading the rpms on the lap top connected to the ecm compared to the guage)What would it take to cut the pulses in half?

What engine? T4?

I'm guessing you are running waste spark.
Need to adjust the tach output from the ecu.

No,carb'd LS series.The MSD unit apparently makes the tach read 2x's the actual reading.

What tach are you running? 914?

Yes.

I think there is a thread here, swapping a capacitor or something.

BTW, a 5" Autometer tach fits right in the stock dash if you want to go that route.

I dont want to.VDO! :DThere probably is a thread about it,damned if I can find it!

so you're running a 4 cyc tach on an 8 cylinder engine. . of course it will read double. .

You could just send it to Hollywood speedo, Palo Alto Speedo or Redline Gauges to have it re-calibrated. I'm sure there's a shop close to you that does this too.

You could also pull the guts out of a V8 tach and stuff them into the 914 tach.

Search is your friend...

http://www.914world.com/bbs2/index.php?sho...ate+tach+for+V8

MSD actually has a tack adapter to be used when using old analog tacks but I'm not sure if that would work in this case. You need to reduce from 8 to 4 so this might work.

http://www.autosportlabs.com/tach-adapter-p-65.html

It is used primarily for EDIS since you have 8 spark pulses for 4 cylinders. It is a cheap product and requires very little skill to install inline with your tack output. I don't know what your ignition output is like so just a guess that this may work.

I don't think that will work after looking at the install. It is looking for multiple coil signals and sums them together. He needs to half his signal. This can be done by fiddling with the guts of the tach, or replace the guts with a modern replacement.

If you are really handy with a soldering iron, you could make a pulse halfer with some op-amps and a counter. Maybe $20 in parts but you will have to find the schematic online or in a book.

This will work for you. Dakota Digital

The mod write up I did about 10 years ago will also work. I've done 5 tachs so far and all of them have worked good with the V8.

Bob