AC Idle up

Tuning, troubleshooting and the nitty gritty of using rusEFI to make your engine run nicely!
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Kristian
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Joined: Sat Apr 09, 2022 10:34 pm
Location: New Xiland

AC Idle up

Post by Kristian »

Hi guys, please forgive my upload for Sharron's roadster, I have a bit of a question around idle up of the AC. I have been reading the idle explanation and I can see that I still have a bit of work to do around tuning that. So tonight I went out and tried to hunt down the issue of why the car rockets up to some 2500rpm when the ac compressor comes on. and when it goes off, it sometimes jumps to 3000 and just sits there, as if the changes applied to compensate for the load are still occurring, but there no load to pull it back down. I've been screwing around with the openloop and close loop idle settings to see which one might make it transition a little better, but I couldn't get it to dial back to ~1200RPM. Reading the post about setting up for a rock solid idle with no load and then some load, got me thinking that I might have to go back to the drawing board and have another crack at getting that a little more stable. I'm not sure if I've seen the AC run at a stable ~1200 RPM, so unsure if this is another setting that I've simply overlooked.
I've added the tune and log file to online. https://rusefi.com/online/view.php?msq=966

Thanks in advance

The car is a 91, normally aspirated M5, relatively stock with an AFM delete. its running mid grade 95 RON (which might be your 89). Side note, for comparison most cars in this part of the world run 91 RON (lowest) and most stations sell 91, 95/98 and 98 with 10% ethanol.
1991 1.6 Mazda Eunos Roadster, 5sp, Normally Aspirated
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Kristian
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Joined: Sat Apr 09, 2022 10:34 pm
Location: New Xiland

Re: AC Idle up

Post by Kristian »

I made some changes back to more stable figures within Idle control. noticed a couple of interesting things.
1. the idle up that I had noticed wasn't AC, but fan 1, obviously, becuase AC turns Fan1 on, I hadn't noticed the less obvious connection. When testing the Fan1 output from the base engine tab, with AC off, the RPM would rocket upto 3000 odd RPM, removing the association with the AC meant the engine didn't spool up, rather loaded down and nearly stalled when AC was turned on. When Fan 1 comes on, the idle valve position goes from, say 17, to 40, then oscillates quite rapidly between 40-100%.

the second interesting thing I discovered was a let-off table that in the idle tab that I thought was disabled (I had turned open loop idle to on, which greyed out this option, but left on true) it seemed to follow this table (which was 40% for all values.) modifying these down to 30, caused idle oscillations to occur, so even though the option was greyed out because of openloop idle, modifying this table had an impact on the car. I could also swear that as I was driving a long, small power surges could be felt after a gentle press of the gas peddle. I went to the enrichment tab and found a lot of it greyed out. However I suspect it may it might still be using some of the figures.

So from here, still a bit of work to do understanding how this works, when tables are being used and when not, and try to understand the link between fan 1 and the mystery 3000 RPM 'idle" (even thou the idle tab shows a 100rpm increase for fan 1)
1991 1.6 Mazda Eunos Roadster, 5sp, Normally Aspirated
mck1117
running engine in first post
running engine in first post
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Re: AC Idle up

Post by mck1117 »

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image.png (22.85 KiB) Viewed 2091 times
These settings say:

- Set idle position to 28% * CLT adjust table
- Add 5% if AC is on
- Add 100 RPM to the closed loop target if AC is on
- Add 100% if fan 1 is on (?)

That last one doesn't look right to me - do you really want to add 100% (ie, max the idle valve fully open) if the fan is on?
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Kristian
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Location: New Xiland

Re: AC Idle up

Post by Kristian »

Good spotting batman! I completely missed the % and read it as RPM as above. That kinda makes sense why it could have been switching to the coast down table, (even if i had changed to openloop and had assumed it was no longer in use.)
1991 1.6 Mazda Eunos Roadster, 5sp, Normally Aspirated
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