ICM Set Timing ???????

[95 3-4]

Does the icm set the ignition timing ? i went to start my car today and it sounded like the timing was way off 1st attempt at starting failed second attempt timing was off different now, now its to far advanced, made the engine stop cranking 2 or 3 times by firing to early but it caught idled choppy for a sec then smoothed out to nice 1500rpm cold start then idled down to 1k.........so does the icm set the timing or is it the ecu and where is the icm, is it what the coil packs are screwed to ?

 

Come to think of it the first attempt made it seem like the firing order was wrong the way it was cranking, i thought oh my cam belt puked, but it runs fine so it couldnt be the cam belt

[Redfox340]

No, the ECM is always anaylizing data from different sensors to tell when the spark plugs fire. The Ignition Control Module (ICM) is plugged into the ECM and when the time is right, the ECM tells which cylinder to fire. The coils on the ICM are nothing more than big capacitors so that multiple spak plug fires can happen within a minute.

 

If I was to guess, I'd say you ICM is going out, or you've got a bad plug / wire / coil pack / connection.

Double check those components and see where you end up.

 

- RedFox340

[brian89gp]

Not sure on your problem but this is how the setup works.

 

The ICM controls all timing and which cylinder fires and under 400rpm the ICM also controls the amount of spark advance/retard. Above 400rpm the ECM calculates advance/retard, disables the auto calculation for advance on the ICM, and then procedes to transmit advance/retard rates to the ICM. The ICM still controls which coil fires when no matter which mode it is run in, it just uses the ECM input when its told to.

 

As far as I can tell the ECM on MFI engines doesn't even know which cylinder is TDC just that one is among the 6 is; the ICM provides the ECM with pulses so that it can calculate TDC. Think of each pulse as an event, and for each event the ECM figures out when to fire the injectors (all 6 are fired at once) and how much spark to use. There are 3 events per RPM and 6 events per cycle. SFI systems are completely different.

[Redfox340]

Brian89gp, thanks for the clear up... I had a good idea, but yours is most helpful!

 

- RedFox340

[brian89gp]

I just noticed you have a 95. Have you tried pumping the gas while starting it? I know it sounds odd for a fuel injected vehicle but it made mine easier to start.

 

The rev up to 1500-2000 is normal.

 

I think its a 94-95 thing, I could sit there and crank on it for 5-6 seconds before it would start, sometimes it would just stumble around like it was missing horribly, and other times it wouldn't like to stay running on the first attempt. The first time I started it with a 93 wiring harness and ECM it fired right up before I could take my hand off the key, so its definately related to the 94-95 ECM.

[SmokesGTP]

Its true pumping the gas does make it easier to start for some reason. Its also easier if you wait 5 or 10 seconds with the key on accessory before turning the car over so the fuel system pressurizes and you can hear the fuel pump click on. My car usually starts crappy and if I stab the gas once before I start it, it will start much easier.