Megasquirt Injection Timing
Turbo Mini Forums

I'm investigating what the standard MS2/extra code does before I rip off the carburetor.

The Megasquirt is all set up, running the ignition and I've wired in the four injectors. The injectors do not have any fuel supply and they are just hanging in thin air.

I don't have a scope, but the inductive clamp on my timing light picks up the injection pulse from the injector wiring.

Hence, i can see, more or less where the injector fires.

Anyway, it appears to fire at a fixed point corresponding with BDC on cylinder no. 1.

It retards with revs, so i'm assuming that the timing light is picking up the end point of the pulse. Would this be right?

I'm doing this because before running the siamesed code, i want to verify everything is working Ok with the proven MS2/extra code, even though I don't expect to get even fuel distribution.

I'm going to do some calcs to see what the likely impact of this is.

Edited by Paul S on 5th Jan, 2008.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Connect you signals to the micro laptop input through 10k pots. You'll get a 2 way scope, you'll be able to watch the reference and the injector signal.
The strobo lamp could react at both pulse edges depending on the clamp circuit you have on the injector outputs.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

It would make sense that it's picking up the end of the pulse because that would correspond to the flyback voltage from closing the injector.

Are you using high impedance injectors? If you're using low-impedance with the PWM setup in MS then I don't know what you're picking up because you have much more going on then.

Also, is it retarding a lot or just a tiny bit? If it's just a little, it might just be some computation time before injection which is a constant time but will look like retarding the injection with higher RPM.

Jean

http://www.jbperf.com/

They are high impedance injectors.

The retard is around 10-15 degrees at 3000 rpm. Stationary.

I checked it again with one eye on Megatune. The injector pulse width hardly increased so it seems a bit strange.

It's only about 1 ms, so it could be computational time.

I've done some simple air velocity/time calcs and it looks like the fuel will hit the inner cylinder inlet valve about 90 degrees ATDC at idle. This means that the inners should run rich. However, at higher revs, the impact may not be so great.

It will be interesting to see if the results match the theory.

Tomorrow, I start fitting the injection manifold and FPR etc.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

The standard code just starts the injection after the trigger tooth for the ignition. It does all it's computations for the ignition time and dwell then starts the injection pulse.

So what you are probably seeing is the end of the pulse that was started some time before TDC (depending on where your ignition timing is set). Since this is a fixed time for the computation, it will mean increased degrees as RPM increases plus whatever pulsewidth increase you have. Also, if the ignition timing increases, then it will trigger from an earlier tooth which will advance the injection timing (which is actually not a bad thing in this case).

Jean

http://www.jbperf.com/

any one here

@ newguy1,

Hello but basically you have found a five year old thread.

For those of using MegaSquirt on the A series for sequential injection (either MS2 siamese code or MS3x) the info is unfortunately rather dotted about the forum.

You will have to search, depending on what you want to know, but it is all there.

Schrödinger's cat - so which one am I ???