Blactop 20V 4AGE seems to have an intelligent ignitor

[Hen]

A bit of CRO testing uncovered that a blacktop 20V ignitor is intelligent (which is annoying). The signals looked like the picture below (all measurements taken at or around idle). Note, I don't have a fancy CRO that can take screenshots, in fact I have a crumby CRO, so I have to rely on my MS paint "skills".



(I'll also describe it in case the picture disappears).

- The IGT signal is usually 0V, rises to 5V for a moment before dropping to 0V to trigger a spark.
- The coil negative signal out of the ignitor is usually 12V, then drops to 0V BEFORE the IGT signal rises, then rises again to 12V exactly when IGT drops (triggering the spark).
- The G1 and G2 signals out of the CAS are falling edge, and occur during the dwell time of every 4th spark. The falling edge occurs while the coil negative signal is at 0V. This is true for both G1 and G2.

So it seems the blacktop ignitor is intelligent. This is also supported by its guts, I pulled it open and there is a lot of circuitry in there, far more than just a big transistor.

I'm posting mainly for future reference, but also to see if my reasoning is correct.

Hen

[Cdr Zero]

Why is an intelligent ignitor annoying? (curious)

[Hen]

It makes life a bit harder if you want to ditch the dizzy and run 4 coils. Something needs to do dwell, and it isn't the ECU unfortunately.

[Sam_Q]

I thought all 4age engines had smart ignitors?

[thechuckster]

Cdr Zero: a 'smart' igniter does dwell control for the coil. It, not the ECU decides when to 'charge' the coil before turning coil voltage off to make the spark.


Hen: you can get bosch ignitors that do smart or dumb dwell. Likewise, GM HEI modules will drive a coil from a VR-like signal.

G1 & G2 wont be used for any dwell control - they're just for crank/cam positioning (and indirectly coil selection if its a 4agze or 7mgte or 1/2JZGTE).

Does the dwell amount vary for different RPMs and system voltages?

your MSpaint diagram suggests that it has a fixed (%) duty for coil charging.

and if you are converting to waste-spark or sequential CoP, then you're changing ECU to an aftermarket ECU - and many if not all can switch between driving dumb and smart ignitors?

[Hen]

Close Chuck, I'm trying to switch to twin/four coils, but keep the factory ECU (a just put up a thread about the plan for that too), so it can be mounted in a RWD without the dizzy sticking through the firewall.

As for dwell changing with RPM, the engine had no cooling system attached, and we were running it late one evening with just extractors on, so I didn't get to check closely.

I'm starting to think I could forget about dwell and just use some smart Bosch ignitors. That may take some more experimenting though.

Hen