sync loss during cranking

[billjam]

I am having brutal kickback on the starter during cranking and it seems to be related to sync loss.
I have previously adjusted R52 and R56 to tune out some sync loss issues in the past and I'm wondering if further adjustment here might help. If so, which one?
Logs and msq attached.

[billr]

Or, is the sync-loss because of the "brutal kick-back"? Reduce cranking ignition advance to zero degrees, see how that does.

[dontz125]

Your ignition advance was already pretty low. Have you checked the #1 trigger angle with a timing gun?

I agree with your thought that the sync loss is caused by the kickback - a sudden reversal of the crank will certainly cause the trigger pattern to suddenly go wrong.

[billjam]

Or, is the sync-loss because of the "brutal kick-back"? Reduce cranking ignition advance to zero degrees, see how that does.

That makes sense, but I have already played with the cranking advance to try and overcome this.
My starter has recently died because of the treatment it has been getting (the sprag clutch is toast and can't transmit power anymore). When I get new parts, I will wind back the cranking advance and try it again just to be sure.
However, there is another issue that I have raised in another current thread which I initially didn't think was related, but now I'm not so sure. The engine won't run below 1000rpm. As soon as revs drop below 1000, the engine just dies.

[billjam]

Your ignition advance was already pretty low. Have you checked the #1 trigger angle with a timing gun?

I agree with your thought that the sync loss is caused by the kickback - a sudden reversal of the crank will certainly cause the trigger pattern to suddenly go wrong.

I have checked the actual timing with a gun some time ago and it was as it should be, however it is worth double-checking just to be sure.

[cmonref]

BillJam,

#1 Your cranking RPM is set at 500 RPM but the engine actually cranks at around 350. You might try 300 as the cranking RPM. That is what I use on my 1980 911SC. That won't have anything to do with the engine dieing at 1000 RPM, but might help the starting.

#2 You have ignition advance at 5 BTDC at <= 1000 RPM. A tweak will be to raise the advance in two stages under the designated idle speed. Say 5 BTDC at 1000, 8 at 800 and 12 at 600. That will give a "catch" of idle dipping below the designated RPM, returning it to the designated RPM. You won't see any benefit until you solve the "won't run at less than 1000 RPM" problem, tho'.

#3 In the MSL, the AFR goes to exactly 13.7 for several seconds before the RPM drops to 1000. The AFR does not vary or wiggle in the slightest, even tho' the PW and MAP are varying. Do you have a lower limit programmed into the tune so the AFR does not drop below 13.7? I do not know if you can do that or not, but it sure seems like it.

Brian

[billjam]

Brian, and others ...
Good news ... I finally got my starter fixed over the weekend and managed to get to the bottom of my difficult starting problem and the inability to run below 1000rpm.
Starting problem due to violent kick-back was all but eliminated by setting cranking advance to minus 10 degrees. I had tried different settings but never went below zero as I didn't realise that negative cranking advance values were possible.
Based on input on the Pelican forum, I reset R56 and R52 to fully CCW and 1 turn CW respectively and now I can get idle as low as 400.

[billr]

Is there any real difference in cranking/starting time due to that ATDC cranking ignition timing? That's the only argument I ever see for using a bunch of BTDC timing, that starting is "faster".