Where tap ignition 1 signal?

s300 and SManager software questions & answers
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Furble
Posts: 53
Joined: Fri Jun 12, 2020 12:55 pm

Where tap ignition 1 signal?

Post by Furble »

Obd1 P72 ecu, distributor is also obd1.

Installing a Plex Knock Monitor. In order to enabale it’s individual cylinder knock detection I have to supply it with the cylinder #1 ignition signal (low volt/before the coil). Can’t figure out which pin this translates to in the ECU, or if it is even in the ECU. It may have to come from inside the distributor cap.

I see pin A21 is for the ICM so that is promising but I don’t know if it pulses just for cyl1 or once per cylinder.
TTR
Posts: 106
Joined: Wed Mar 31, 2004 8:48 pm

Re: Where tap ignition 1 signal?

Post by TTR »

Furble
Posts: 53
Joined: Fri Jun 12, 2020 12:55 pm

Re: Where tap ignition 1 signal?

Post by Furble »

It is my understanding from the manual that injector1 is not sufficient for individual cylinder detection and that it had to be from spark. In the instructions they lay out options A,B,CD & E and say only C,D E are valid for this feature. Injector 1 is option A. Wouod it work good enough anyway?
TTR
Posts: 106
Joined: Wed Mar 31, 2004 8:48 pm

Re: Where tap ignition 1 signal?

Post by TTR »

You can do individual but it doesn't really matter. If it's showing knock, pull 2 degrees on a specific cylinder and see if the knock goes away. I've used individual cylinder with a CPR only.
Furble
Posts: 53
Joined: Fri Jun 12, 2020 12:55 pm

Re: Where tap ignition 1 signal?

Post by Furble »

It turns out this can be done but involves a bit of math. An injector pulse signal can be used instead of an ignition signal however that injector pulse must be timed between when cylinder #1 is between 20-90 degrees BTDC, or in other words that injector has to be firing at about the same time the spark in cylinder #1 is firing. Since the injectors fire 400-500 degrees BTDC of the compression stroke you could work out which injector happens to be at the right place at the right time in the cycle to match up with ignition1. However I decided to keep it simple and just go with knock vs rpm rather than per cylinder which is hard to action on a distributor ignition anyway. Just putting this info here in case anyone else wants to work out the math and try it.
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