Ignition Control Module

[RoboGeek]

Has anybody ever sniffed the control line from the PCM to the module? I want to find the info getting sent that controls the spark advance. Just curious if its a timing bit, a hex bit, or an analog voltage even (yes I have no clue!)
I'm assuming its a timing bit (spark triggers on reciept) rather than actual coded info.

I'm getting sick of pulling and flashing to change stuff a few degree's. So I'd like to either be able to change it at the module on the fly so I can find the optimum setting.. or use that instead of tweaking the spark tables

[Keith@HPTuners]

I believe its just a timing bit..

For a while on my 3.8 I was using a MAF T+ to change timing.. basically you tap into the signal wire from the PCM to the ICM and the MAF T+ does it's work..

From what I gather, it listens for the signal then makes an advance or retard of that signal for the next "theorized" moment of spark and sends out the new calculated spark signal, ie: 2 degrees sooner or 2 degrees later. Seems like it would alawys be a few cycles behind, which really isn't that big of a deal.

[RoboGeek]

About what I figured. I know some modules run in a limp home mode if theres no signal. The computer changes amount of retard from the 86º or whatever advance the crank sensor runs at. So it just seems like limp-home would be full advance instead of full retard like I would think it should be. Maybe the module has more ability than it seems at first glance.. ;D

[The_Raven]

This is exactly what I have been thinking about, well very close actually, first which pin is it you are refering to? forgive me for not remebering the names or pin locations, it's late all I can remeber are colurs at this point. lol

The following applies to my ECM/ICM combo, which is a oh crap I can't remeber the service number, but the ECM is from an '89 Z24, and the ICM is what would have been used with that, it is a DIS ignition system, most GM systems that I have seen are similar, except the newer GM trucks, not sure what they are using exactly, but I believe it is triggered directly from the PCM. Anywhoo....

There are 4 wires:

-Black/Red ground from ICM to ECM, which I believe is a ground reference between both.
-White Refernce low. Signal from ECM to PCM to control actuall spark timing, so far the info I have found indicates this is an analog voltage, I have measured the output with my DMM and seems to somewhat confirm this
-Purple/white refernce high
-Tan/Black EST output, this goes to ground from the ECM so that the ICM will listen to the ECM for advance/retard info.

I'll look through my books tomorrow, and verify this.

What I am looking for is someway to control timing under boost, a lot like an MSD Boost Timing Master, but interfaces with the OEM ICM, since I don't want to spend $1000+ CDN on an ignition box and BTM, I can get an aftermarket ECM for a little more.

[RoboGeek]

I've been told that if you disconnect the ECM the module will still work in limp home mode. Which means it gets a raw signal from the crank sensor and conditions it, sending the new signal to the ECM for timing info to be returned to it. This I'm not sure of since my manual is pretty unclear. But it does show the wiring routed that way. The older ones dont seem to be set up like that i.e. the crank sensor goes to the ECM instead of the module.

If it does work that way then it would be simple to build a spark controller program/module that only runs spark. You would only need to create a timing signal to the module and not have to worry about finding TDC etc, since the module would have to be doing the timing reference instead of the ECM.

btw.. building in spark retard is easy. There are lots of ways to delay the timing trigger, either hardware (MSDII type) or software (programmable MSD)
I'm trying to add spark, which is a completely different creature

[The_Raven]

Ahh, so you want more timing then?

I'm not sure what "older systems" you are refering to as having the crank trigger going to the ECM. ???

Mine is an "older" used between '87 and '91 from what I can gather, and the crank sensor goes directly to the module, the 60*V6 ('87 to present) is this way, along with the OHV 4 Cyl (2.2/2.0L) '87 to at least '94.

Wanna enlighten me on the circuit design for the boost retard? ;D I still want the timing to be controlled from the ECM, but retard that signal (timing when boost pressure is present).

[RoboGeek]

Most things are leading edge voltage triggered. As the voltage rises it reaches a threshold voltage and that triggers the signal. A quick way is to just use trailing edge voltage threshold. The event is triggered as the voltage drops from peak. That delays the signal by the duration of the incoming pulse width. Not very accurate..

The best way would be with an algorithm that takes into account rpm and boost and generates a signal for the module. You would basically be taking over for the ECM then. Best was would be with a PIC controller that you could interface with a laptop to tune with. The PIC holds the program and works faster than a serial port on a laptop would. You would just have to write the program then.. PICBasic is pretty easy to program in - thats what my robots run.. ;D

[The_Raven]

crap, I'm gonna have to dig out my electronics books again. :-/

[sean]

or just repin and run the $8f code. tunercat has a tdf for it btw.

[RoboGeek]

TC could save me alot of headaches if they did one for the 2.2... lol
So far nobody has been able to convince them its a worthy endeavor