Inconsistent Crank Fixed Timing

[twelvexs]

Hi all. Back again with another question.

I cannot get consistent fixed crank timing as discussed in the manual. My setup is:

- MS3x, sequential fuel, sequential spark
- 36-1 Crank and 1/2 moon Cam input
- LS2 coils (non truck)
- Tooth 1 angle is 68 BTDC degrees (measured as per MS3x manual recommendation)
- Main wheel speed = Crank wheel
- Second trigger active on = Poll level
- Level for phase one = HIGH

Basic background is that when I try to get test the fixed timing discussed in the manual by setting cranking advance to '0' and fixed timing, I don't get consistent strobing of my timing light. It shows random flashes sometimes 2-3 quickly, sometimes none at all, then sometimes at '0'/TDC.

Just to try, the engine will sometimes try to catch, then sometimes backfire thru the throttle body, to me a good indication what I'm seeing is not just crappy timing light. I've tried 2 lights, both simple non-dialback, and same results.

Anyone have ANY ideas? I put my coils in test mode and get dead on consistent timing strobes from the light, so I believe the wiring is right.

Here is a YouTube video link of the fixed timing at '0' and you can see it doesn't flash consistenly, especially when first cranking, then misses a pulse in there. I can take a longer video if needed as well

https://youtu.be/TnKE-b6KkMY

Attaching my tune and a composite log if that helps. If another log will help, please let me know the parameters and I'll gladly set that up for capture.

Thanks in advance for any help you can provide!!

[billr]

What kind of ignition coils? I see your dwell is set to "fixed" with a duty-cycle of 50%. I'm not familiar with how that works, but it sounds like it is a lot of dwell while cranking. Some LS-variant coil type is sensitive to "over-dwell", will fire prematurely.

[jsmcortina]

LS coils need real dwell. Using "Fixed dwell" may damage them.

James

[twelvexs]

@billr

Thanks for the reply. I'm using LS2 coils and configured as shown in the MS3XV357 manual, section 5.3.2 Logic coils. I didn't see (or missed) any setting about 'fixed' duty, however that makes sense if it's a 50% dydte cycle regardless of the dwell time period specified. I was following the Megasquirt3 Setting Up-1.3 manual where it says in seciton 2.12.5 "Each setting needs to be reviewed and set appropriately, however, if unsure, leave alone!", so I left it alone!!

@jmscortina

Thanks for the input. So just to confirm, I should use 'Standard Dwell' or which of the other pull-down options for Dwell Type; this will utilize the dwell setting specified in the boxes above?

From my reading, about 3-3.5mS of dwell is probably quite enough once I get things moving in a different direction. Does that sound about right?

I started with the published Mustang MSQ tune from diyautotune-I'm guessing this might be where the 'fixed duty' came from. I'm not using the TFI distributor/spark control at all.

Thanks guys for the pointers. Will give it a crack tonight when I get home.

[twelvexs]

@billr and @jmscortina

Guys, thanks for the pointer here. Made that one change and completely fixed the situation. Engine timing was spot on after that, it then stumbled to life, and warmed up great after that.

Now it's off to learn how to tune.

Thanks again!!