4.0L Tach Install Question & Rough Idle

[AgPete139]

Hey Guys,

I bought a brand new Super Pro 3" tach from a guy on Craigslist for $15 last week.
No cut wires, or tampering, but it does have a small external scratch from storage.

So here I am. I took the tach apart and switched it for 6 cylinder engines. I spliced the GREEN WIRE into what I believe is Pin 48 on the passenger side firewall for my '97 4.0L w/ the 5R55E. It was BROWN w/ YELLOW stripe, and I never saw a TAN w/ YELLOW stripe in the cluster. I roughly tested all the wires in the engine bay to get the tach to work, but it just vibrated above the 0 (almost 50-100 rpms). I hit the throttle and the needle only jumps up to ~ 900 rpms (normally ~4500 rpms).

WHAT IS THE PROBLEM?

I have tried to figure this one out, but can't figure it out. The power is correct, the ground is secured, and the only thing I can guess is the green signal.

For the record, my engine has not been liking the cold and tends to die in the first 10 minutes of operation in 50*F weather (which is one of the reasons I want to monitor my truck, and cause I've been wanting a tach for a while).

I've referenced:
TRS Tech - Tach Install
RPS Tech - Tach Install by Fastmofo
Random TRS Tach Install thread
Quote taken from another 4.0L tach thread:

Yo,
Before i read the article here on TRS, the instructions that came with the tach suggested i use the wire that came off the coil pack. (They obiously did not design it for a ranger.) That diddnt work so i found on the site that Ford already wired for a tach, even if your model diddnt come with one. So i found the wire they talked about (The tan one i believe). And it worked just fine.

Reference for people later:
Red wire = power
Black = ground
White = gauge illumination
Green = tachometer/rev signal


HELP!

Thanks for everyone's help in advance,
Pete

 

[MAKG]

I'm not sure of the color codes, but it sounds like you're having issues with the EDIS ignition.

Most tachs expect a signal that fires for EVERY cylinder. You have to do that if there is only one coil; then the distributor launches the spark to each individual cylinder. You have three coils.

I believe there is an appropriate signal at the ignition module. Or there MAY be a setting on the tach for it. You can try to call the manufacturer and ask what to do about distributorless ignition. It's quite common these days.

 

[AgPete139]

I'm not sure of the color codes, but it sounds like you're having issues with the EDIS ignition.

Most tachs expect a signal that fires for EVERY cylinder. You have to do that if there is only one coil; then the distributor launches the spark to each individual cylinder. You have three coils.

I believe there is an appropriate signal at the ignition module. Or there MAY be a setting on the tach for it. You can try to call the manufacturer and ask what to do about distributorless ignition. It's quite common these days.

I remember reading about that. Where would another signal (with all 3 coils combined) would be? I am hoping do all the wiring in the dash and have it come out to the steering column...

The EDIS has to have another signal. Anybody?

 

[AgPete139]

BUMP !!!

For more input...still needing to know which wire in the dash for tach signal...