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PID Idle Closed Loop Idle settings in MSII
https://www.slantsix.org/forum/viewtopic.php?t=68424		 Page 2 of 2
Author:  Greg Ondayko [ Mon Nov 24, 2025 9:29 am ]
Post subject:  Re: PID Idle Closed Loop Idle settings in MSII
Quote:
I'll need a log of the oscillation to see how that tune is working in the real world, but my prime suspect right now is that abrupt jump in the fuel table between 44 and 48 kPa. Also, that's not very much timing at full throttle.
Thanks, Matt.
I will see about getting a log. Last few starts have been sublime - Either at full cold <50° F or full hot without heat soak >195°F

I think the low full throttle timing is there to avoid the ping with a stock 1979 Cam and ~9.5:1 Compression. Short duration / low overlap stock cam bumps up the DCR a bit is my guess here.. I will see if I can get it to log and visit the oscillation nation.
Author:  Greg Ondayko [ Tue Feb 17, 2026 5:46 pm ]
Post subject:  Re: PID Idle Closed Loop Idle settings in MSII
Here is a Startup Log.
The O2 Does not send any data until about ~25-30 seconds in to the log as it takes time to warm up and reports an AFR of ~7.XX which is not accurate.

Thank you, Greg
Author:  Greg Ondayko [ Wed Feb 18, 2026 3:17 pm ]
Post subject:  Re: PID Idle Closed Loop Idle settings in MSII
2/18/26

2 More Logs to toss on the fire... Keep warm.
Cold Start CLT = ~56°F
Warm Restart CLT = ~195°F No oscillating here.

Greg
Author:  Greg Ondayko [ Thu Feb 19, 2026 1:05 pm ]
Post subject:  Re: PID Idle Closed Loop Idle settings in MSII
2/19/26:

4 logs for the fire today.
Cold start Morning
Hot Restart Morning

Cold Start Afternoon
Hot Restart Afternoon

No Oscillating on any of them.

I will not post more logs until I can capture a (hot restart) Oscillation.
Author:  MadScientistMatt [ Sun Feb 22, 2026 5:40 am ]
Post subject:  Re: PID Idle Closed Loop Idle settings in MSII
One thing I can see is that sometimes when it starts idling poorly and pulling low vacuum, you run into the very low timing area of your spark table, which makes it run worse - a bad feedback loop. Try making the spark advance a uniform 12 degrees at all 400-900 RPM points in the table and see if that helps.
Author:  Greg Ondayko [ Sun Feb 22, 2026 7:52 am ]
Post subject:  Re: PID Idle Closed Loop Idle settings in MSII
Quote:
One thing I can see is that sometimes when it starts idling poorly and pulling low vacuum, you run into the very low timing area of your spark table, which makes it run worse - a bad feedback loop. Try making the spark advance a uniform 12 degrees at all 400-900 RPM points in the table and see if that helps.
Thanks Matt, That is easy to do. Getting snow again here now for a few days, so when the salt and snow goes away I will get to test the changed timing.

Greg
Author:  lgu32 [ Sun Jun 07, 2026 9:37 pm ]
Post subject:  Re: PID Idle Closed Loop Idle settings in MSII
I have a Maxxecu both in my slantsix car and turbo-Sporster. A slantsix has an idle valve but Sportster dont. For the Sportster I have only the idle timing to get idle speed controlled. However it will need quite wide are of timing to get the target rpm on. And because this timing variation of ignition will cause afr changes the idle PID will modulate the afr PID. It was a nightmare to get working smooth. With lightened crank the engine stalls easily. So I left closed loop and did for the idle just a table like this:

Image

There is several columns for ignition degrees compared to rpm and rows for getting the engine temperature together. All is open loop. It keep the idle within 100 rpm but does it so smooth that the AFR PID doesnt disturb. A Maxxecu ECU is nice to do things you develop yourself.
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