DriftTrix

I just got a SM4 installed into my FD. It works like magic but the only problem was Justin at AlienAuto didnt know a way to hook the stock tach up to the SM4 and have it successfully messure RPM. I think it was related to the voltage output of the SM4 to the desired imput into the stock tachometer. If you guys know a way i can get the two joined together and working like clockwork it would really help alot!

Or justin if you read this and you got the way now let me know!

enzo250

FD tach works with a regular 12v square wave signal.
SM4 tach output is a 12v square wave. It should work no problem.
Are you sure you have set the output to tacho and are you positive your using the correct wire? What are you using for ign?

DriftTrix

I didnt put the SM4 in. Justin the autronic dealer in Washington did and it sounded like he had problems hooking it up. So it should hook up no problem?

I run a AEM C2DI 4 channel ignition moduel and 4 MSD ignition coils.

enzo250

wow.. Good luck with that aem cdi. I've had quite a few of them go up in smoke.

The aem cdi has a tacho output. Did you try that?
if that doesn't work you shouldn't have any issues using the SM4 tacho output.
Have justin call me if he needs help.

Bad2ndgen

Enzo, I did hook up the tacho output but couldn't figure out how to make the sm4 fire it on each leading ignition event? As I understand it the factory tach is triggered off the leading coil wich is wasted spark thus firing twice per engine cycle... Sence I converted the setup to four coils I was unsure how to setup the tacho output?

PS I warned him about the c2di...pos

Justin

enzo250

So what do you see? Does the tach work at all? Is it reading only half of what your actually revving?

DriftTrix

The tach doesnt move at all = ( If it was only half i could work with that but its pegged low

enzo250

Well something is wrong then. You probably have the wrong wires hooked up or maybe the ground is missing. There's a ground in the passenger kick panel that needs to be grounded in order for the gauges to work. Is your water temp, speedo, etc working?

DriftTrix

water temp and speedo work fine. Water temp is really off tho, half way up is massive overheating and just above the second cold line is perfect

onefastrx7

Is this a brand new CDI ( just built), or from an old batch?
The new AEM C2DIs have been tested to work perfect. The old ones were pos.
I talked personally to Jason at AEM about all that. Many DSMs use them with no problem. Several RX7s and 20Bs run them with no problem as well.
I had issues with the old ones as well

enzo250

they could promise whatever they want. I will never use any of them.

crispeed

I new someone that had problems with the new one(Rx-7 application) also.

crispeed

An easy way to figure out if you're using the wrong wire to trigger the tach would be to use the tach output on the check diagnostic plug. The one on the driver's side shock tower. That always work. I sometimes even used that when MSD's are involved especialy when they are mounted in the engine compartment.

DriftTrix

How can any part of the ignition system be hooked up to the diagnostic plug if its all aftermarket. The coils/c2di/autronic ecu is all wired together i dont see how it could/would go through the plug...?

enzo250

Because if that wire goes direct to the tach then hooking up a tach output to that wire should display on the tach.

DriftTrix

speaking of C2DI. It was one from the new batch, and it went out = D. They're going to send me out a loner untel the new system comes out in a couple weeks. splitfire 2 or spitfire 2, something like that.

They're still pos's

ill try the diagonistics plug after i get the loaner. see if that works

thanx for the help so far!

**Edit: Would you be able to tell me which wire going into the diagnostic plug is the tacho output? i could try them all but it would make it easer**

pluto

just hooked the tach to the leading output on the SM4. I assume that you're running waste spark so it should work fine. the ignition output is 0-12V before the AEM CDI

crispeed

It would be the Y/L wire or yellow with a blue stripe. I believe it's the IG- in the diagnostic connector. The rpm reads correctly from there when connected to MSD's tach output.