Hey! My b2600i 4x4 truck is running on a speeduino. I honestly haven't spent much time tuning it, I got it running better than it ever did on the stock ECU and have mostly just been driving it.

That said, there's one super annoying thing it does and I'm not sure why. Sometimes when cranking to start it, it will "kick-back", as if it's spinning the motor the wrong way and grind the starter, and the tach kinda jumps. Though most the time it just works and starts fine.

My suspicion is something with cranking timing, but curious if anyone has ever come across this or has any suggestions on where to start.

Thanks!

 

That is probably correct.

Check what timing you are using in the upper right section of the timing table.
That is very low rpm, but high manifold pressure. That is where it runs when waiting to ignite.
Also check cold temp timing advance and cold crank timing advance.
Maybe back them off

 

Does the timing wheel have only 4 nubs, like a stock Miata? If so, Reverant recommends-1 BTDC cranking “advance”.

 

If you go into tuner studio and go to Spark->"Spark Settings" you can adjust the cranking timing. I have pretty good results using 10 degrees on my Miata. I used 6 for a while in the past which worked, but I think (possibly all in my head) that the car starts easier at 10.

I assume you verified your trigger angle and base timing?

 

I'll start here, current cranking advance is 14*, and the transition to spark map (upper left hand corner on my map) where it's low RPM but ambient KPA it's targeting 14* as well. Thanks for the input though, it helps me know where to look. It makes sense that changing just the cranking value didn't seem to change much on this scenario, I might need less timing in that part of the map.

I did check cold temp advance and that was zero'd out, but I didn't find the cold crank timing advance setting. Not sure if I have that in my firmware.

To be honest I'm not sure timing wheel is inside the distributor. I was able to get it running using single channel spark, going low trigger, "Basic Distributor", with "New Ignition Mode" enabled. However, thanks for the info, I'll try much less cranking timing and see what happens.

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Thanks for the tips, yeah timing offset is dialed in and verified.

 

I may not have much to add but here’s Rev’s thread that was referred to above. Interesting concept but makes lots of sense.

https://www.miataturbo.net/megasquir...9-05-a-108062/

 

I adjusted the cranking timing to 6* from 14*, and the area in timing map where it would hit while catching/starting to the same 6*. All seemed good, until later on a fully cold start leaving work it did it again. I wasn't taking a log (damn it, next time I'll be sure to log my starts), but I was watching the timing map while it happened to see what timing values it was targeting. I saw while it was cranking, before it went into kickback that it spiked rpm signal to 4200 or so RPM and was using the ~31 value I had there, which kicked it back. So now I'm thinking it's a trigger pickup thing where it missyncs or something.

I changed one setting I saw that I thought could help, "Skip Revollutions(cycles) was set to 1, and I set that to 2 hoping it would have a bit more time to sync before firing in hopes that would help. I can deal with the extra cranking time if it fires nicely everytime. Maybe I'm way off on this, but I'm going to start logging cold starts that way if it happens again I'll catch it.

 

So far, Skip Revollutions(cycles) being set to 2 instead of 1 appears to have fixed the issue.

Now the car takes a wee bit longer to start though when cranking. That said, there's still room for improvement in my cold cranking/start settings, so hopefully I can get this to fire a bit quicker and still not have the kickback issue.

 

Your theory on that above makes sense. Maybe that extra cycle to get sync is what the ecu needed.

Forgot this was a distributor system. No experience with that, but glad that its working.