Any of you guys had to do this? I really don't feel like asking the fawking Lightning Conversion guys(are they still around?). From what I've heard, it sounds like it is just some diode or something. I was going to spend the money on one of those sweet 5" tachs and milk the "Import Racer" thing, but then I wouldn't be able to see out the little windsheild!

Essentially, it is a diode that you need to wire inline. The problem is determining the correct resistance diode. You can use a potentiometer to determine the correct resistance and get a diode to match, or you can get an aftermarket setup (I think JEGS sells it) which matches up the cylinder count of the motor to the cylinder count of the tach for you.

Matt

Originally posted by ManglerYJ
The problem is determining the correct resistance diode.

:laughing: I think I've found a new signature line... :D

A tach works by counting pulses. The tach must be designed to allow recalibration for the different number of pulses per rev. Most aftermarket tachs have a switch which changes the calibration. Throwing a diode inline ain't gonna do it, you need to know how to recalibrate the Kick tach (if possible). If your year model had a V6 motor offered, check a wiring diagram. There may be a 'strap' or different wire used for the V6.

-or-

V6 - 3 pulses per rev.
I4 - 2 pulses per rev.
Buy a calculator and get good at multiplying the tach reading by 3/4.. :)

I apologize... I mis-spoke. It is not a diode, but a RESISTOR that is needed.



Quoted from BC4x4.com in Chris Waterman's V8 swap info section:


Tachometer: This was a tricky one, with a cool solution. Factory tachometers are typically set up to work with the stock engine: a 6-cyl YJ will have its tach set up for the 6-cyl engine, the 4-cyl for the 4-cyl, etc. This is because the tach works by measuring the frequency at which the ignition module fires the spark plugs, so my 6-cyl tach expected to see six firing pulses per motor revolution. That meant that when I hooked up the V8's tach wire to my old tach, it read high, since the 302's ignition puts out eight pulses per revolution. I spent some time taking my old tach apart, trying to figure out how it worked, before coming across this clever article at Off-road.com. It's an elegantly simple solution to the problem of recalibrating a tach after swapping in an engine with more cylinders than the old one. I used a 1k-ohm variable resistor set to around 500 ohms (calibrated using a frequency meter) soldered across the meter leads inside the tach, and now it reads perfectly. The resistor bleeds off some of the current being fed to the meter, lowering the reading by a fixed percentage throughout the useful RPM range. Easy and cheap.

This may all be as simple as taking the dash apart, but due to my lack of time and patience, I may be better off spending a little cash. Hell, in the time it would take me to tear it all apart, I could have run a decent trail!

Yeah just buy an aftermarket tac :)

The Chris Waterman's method might work, but here's a little info on what he's doing. By adding the resistor across the leads he is pulling down the amplitude of the tach signal. On a simple analog tach, this might (assuming no internal AGC circuit) lower the reading. There is a risk, however. If your tach is connected directly to the coil lead (like many are), and you start putting resistor(s) to ground on that lead, you will also start bleeding power off the coil. That's not often a favorable outcome. Also make sure your tach signal does not go to your computer (assuming EFI). That also could cause problems if you tinker with the signal...

Sorry, I know I'm not helping your problem. However, I don't want you to create more problems in the process. IF the factory tach can work with a V6 there may be a simple solution. Otherwise, you would probably be better off putting in an aftermarket tach. :(

He he, I want to know where that guy found a two stroke 302 (8 pulses per revolution)? ;)

OK has some good points, it is not going to read as acurately as a good Auto Metter, anyway! (especially with nitrous in the OH SHIT position!)