Curious about Idle Timing Control after switching to a 36-2 trigger wheel

[castillaricardo]

Hi all,

Is it common or expected to lower the proportional and derivative gains of the idle timing control when switching to a higher resolution trigger wheel? Since I switched from a 4 tooth to a 36-2 trigger wheel in my MX-5 I noticed that the idle timing control became very erratic with constant jumps to max timing. I had to lower the control to P=0.4 and D=0.07 to make it behave close to how it used to work with P=2, D=0.5 with the 4 tooth wheel. So is this fine, or do I have an odd issue showing up this way?

Logs: https://1drv.ms/f/s!Amu_1gWOWFlvmzvylI-WYSu8K6wN?e=NxtOGx

Tunes: https://1drv.ms/f/s!Amu_1gWOWFlvmziL60snegeHxf7M?e=OC9nSc

Ricardo

[Vaughan]

From memory I wasn't running ignition idle control but I found I could remove all the transient ignition trim when moving to a 36-2 trigger wheel so it definitely does affect timing drift especially on highly varying engine speed

[Adamw]

The ecu can only see a change in RPM everytime it gets a crank tooth so the idle ign function will see a change in RPM much quicker when you have 900% more teeth.   

Dont be alarmed of the timing bouncing around though, that is pretty normal and it sounds like you probably just had less than normal with the old set up. I normally set D to 0, increase P until you either feel/hear the engine get noticeably harsher or sometimes you start to see the dwell get erratic first, then back it off a touch from there.  I usually leave D at 0.  If the dwell gets erratic it means the crank speed is getting too erratic for the ecu to predict position accurately.  Probably something like +/-10% dwell is what I would consider "erratic".   On all of my cars the derivative doesnt seem to help at all, I can usually feel a little more vibration come in whenever I have tried adding D.    Our subaru with 36 teeth has P=1.0, D=0.  A snip of a log below from that car just to give you an idea what I typically see in terms of how much idle ign is bouncing around and what I mean by stable dwell.  The min clamp is 0 and max clamp is 35deg and I can see a range of about 0-20deg in this short snip.

 

[castillaricardo]

4 hours ago, Vaughan said:

From memory I wasn't running ignition idle control but I found I could remove all the transient ignition trim when moving to a 36-2 trigger wheel so it definitely does affect timing drift especially on highly varying engine speed

Good to know! I haven't been using transient ignition trim either and only saw one instance of knock at the track during a big downshift, so I left it alone. I guess with the new trigger this should be all gone now.

 

@Adamw Thank you for sharing an example and giving details on each aspect. It certainly helps to know what to expect as normal. What made me look at the idle ignition was that the engine felt different and there were more vibrations at idle. I'll try D=0 and increase P as you said, but I feel better knowing there isn't an issue caused by the new trigger. 900% more resolution?! I hadn't thought about it that way, but going from 90 degrees per tooth, to ~10 degrees is a big jump.

Cheers! Thank you both!