I just swapped a 99 xj 4.0 into my 83 CJ7 and my stock tach that came with my CJ won't work when I connect it to the neg. side of the dist.

I have read somewhere that this is because of the type of dist on the new engine fires 2x every rotation or something like that.

Any ideas on how to get my old tach to work or what new tach to get that will fit in the hole?

Thanks

-ch

Is your coil mounted in the dist? If you have a separate coil, try mounting it in series with the postive wire to the coil.

you can call HESCO (http://www.hescosc.com/index.html) , they developed the mpi kit for mopar. They know what wire to tap into to get your stock tach to work

Originally posted by combres
I just swapped a 99 xj 4.0 into my 83 CJ7 and my stock tach that came with my CJ won't work when I connect it to the neg. side of the dist.

Are you really trying to connect the tach lead to the distributor? On this motor, try to connect it to the negative of the coil. It should be the gray wire coming from the plug that plugs to the coil.
Hook up the tach, after the engine is running, because some tachs have a low impedance and will short the coil to ground. This will not harm anything, but will prevent the engine from running.
This worked on my 90YJ when I put in the MPI kit. Stock tach works.

Actually when I was saying distributer, I meant coil sorry. long day.

I tried hooking it to the negative side of the coil, and when I put a test light to it it was blinking so fast I coulndt' believe it.

Hesco sucks, overpriced.

I have a CPS installed, I was wondering if I couldn connect it to that, maybe not since it may blow up the CPS.. whcih would be a $300 mistake.

Thx

That fast blink is a surge of voltage, which is what triggers the tach. If you hook up the lead that goes to your tach to that wire, you should get the right reading on your tach. Let me know, cause the information that I found said that 81-90 have the same tach wiring scheme.

Gad, blind newbies:flipoff2: leading the blind ...
Yer old tac ain't gonna work, boys.

The OEM tac runs in-line with the ignition circuit (two red wires) which also goes through the old CJ ignition module.

You need to get an afermarket tach and set it to "4CYL" just like it sez in the MPI instructions for that similar conversion.

The reason for the 4 Cly mode is because of that "2X" deal menitoned earlier...
Your old motor was set up at 6 X2 =12 ... two pulses per revolution.
The 4.0 (at least the 1991-1995 models) are set at "3X" ... three pulses per revolution.
The new tach should be set at 4 CYL beause 4 X 3 =12

Or at least that is how a Jeep Master Mechanic explained it to me... :rolleyes:

Here's what I used and how I did mine ...
Tach for 4.0 induction in a CJ dash (http://www.monsterslayer.com/jeep/DashWork.htm)

I brought this thread back up because I remember this same question came up several weeks ago in another thread. If it's old news, :flipoff2::flipoff2::flipoff2:

I just swap a 95 (OBD-I) 4.6L stroker:) in my 82 CJ and really wanted to use my stock tach. After a little research, I found that the stock CJ tach DOES work with the newer systems at least the OBD-I. The wiring is pretty simple.

The stock tach has two wire on it. A RED wire and a RED/WHITE wire. Find the "IGNITION COIL DRIVER" wire in the harness. In the OBD-I system it is the only solid GRAY wire at the ECM. Cut the GRAY wire and connect the RED wire of the tach to the GRAY wire closest to the ECM. Attach the RED/WHITE wire to the other end of the gray wire. WAAAAAHHHHHOOO!!! It works!!!!

Gripguru's assumption is right at least through the '95 model (OBD-I). Has any tried this for the OBD-II system or the distributorless system?