MSII: PWM Converter Board w/ CL Idle on NB Miatas
11-12-2009, 06:23 PM
#41
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Join Date: May 2007
Location: Columbia, MD
Posts: 248
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Alright, whatever is going on during "strange idle" is not the idle code... That's due to your overrun fuel cut settings. You have it set to 0 seconds delay, above 90 degrees, below 24kPa, and your engine is actually hitting those conditions. So you need to retune that for sure, and it has nothing to do with the idle code. You could probably avoid getting into that situation as well by setting the cranking duty table to a lower duty at the temperatures you're talking about.
The idle after settling bouncing around a bit also isn't the idle code... if you look at the PWM duty it's stable and not moving around. However, your AFR is in the 15's close to 16, and oscillates in time with the engine RPM... I would suggest making the idle a bit richer (14.7 at the leanest, maybe a bit richer).
This will make it easier for the idle to recover from sudden load increases, as well as making it harder to get into a state where it's oscillating. The fact that the PID code isn't responding to the change in RPM is because you've had to set your P term very low to keep it from fighting with the AFR and timing changes. If you can get rid of those AFR and timing changes and richen it up a bit, you should be able to lower the idle a bit and dramatically increase the P term to help it respond to sudden load changes.
On my rx7 (granted, it's a rotary so I have to run a lot richer than a piston engine) I run 12:1 and 5 atdc timing at the lowest loads that I see during idle. The rotary likes to idle at those settings, and it's super smooth. I have my P-term almost at 100.
On the corolla, I idle about 13.8-14.1 and have similar PID settings to the rx7. On that engine the largest sudden load occurs when the fan comes on, and even then the engine drops from 800 rpm to 650 then recovers in about a second.
If I run the rx7 leaner on idle, it starts misfiring and oscillating and then the idle code starts trying to correct for the oscillations.
If I run leaner on the corolla, I have to run about 15-15.5:1 before I have major issues maintaining stability, but anywhere above about 14.5 starts causing small oscillations unless I'm REALLY careful about getting the idle AFRs to be stable all around the idle load and RPM ranges.
Ken
The idle after settling bouncing around a bit also isn't the idle code... if you look at the PWM duty it's stable and not moving around. However, your AFR is in the 15's close to 16, and oscillates in time with the engine RPM... I would suggest making the idle a bit richer (14.7 at the leanest, maybe a bit richer).
This will make it easier for the idle to recover from sudden load increases, as well as making it harder to get into a state where it's oscillating. The fact that the PID code isn't responding to the change in RPM is because you've had to set your P term very low to keep it from fighting with the AFR and timing changes. If you can get rid of those AFR and timing changes and richen it up a bit, you should be able to lower the idle a bit and dramatically increase the P term to help it respond to sudden load changes.
On my rx7 (granted, it's a rotary so I have to run a lot richer than a piston engine) I run 12:1 and 5 atdc timing at the lowest loads that I see during idle. The rotary likes to idle at those settings, and it's super smooth. I have my P-term almost at 100.
On the corolla, I idle about 13.8-14.1 and have similar PID settings to the rx7. On that engine the largest sudden load occurs when the fan comes on, and even then the engine drops from 800 rpm to 650 then recovers in about a second.
If I run the rx7 leaner on idle, it starts misfiring and oscillating and then the idle code starts trying to correct for the oscillations.
If I run leaner on the corolla, I have to run about 15-15.5:1 before I have major issues maintaining stability, but anywhere above about 14.5 starts causing small oscillations unless I'm REALLY careful about getting the idle AFRs to be stable all around the idle load and RPM ranges.
Ken
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12-22-2009, 11:30 AM
#48
Senior Member
Join Date: Nov 2007
Location: Belgium
Posts: 999
Total Cats: 73
Customs decided to release the kit and charge me $76 in the process. How they came up with the number is a mystery, but I'm glad it's here so I can start building 
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Last edited by WestfieldMX5; 12-27-2009 at 05:31 PM.
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