Target AFR in MegaSquirt - Fuelly Forums

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Old 06-22-2007, 12:27 PM   #1
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Target AFR in MegaSquirt

I finally have MegaSquirt basically running now on my Metro. I still need to tune it but it is pretty much ready to be permanently installed now. One of the things I would like to set before actually tuning it is the target afr table. It lets you set whatever you want for the air fuel ratio. I have a LC-1 wideband so I can pretty much get away with anything on the table.



This is what it looks like with the default settings. I figure I can do a lot better then that though. Anyone got any suggestions? I am thinking of basically raising the entire thing by 1 so it would have a target of 14.6 at idle instead of 13.6. I am not sure how much my car can tolerate pushing the limits since it is at 10.5:1 compression ratio it might knock a lot easier running lean.

Also as soon as I get it installed and running well I will put a full writeup on here. It should be real soon now since I have a week or so with nothing else needing done.
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Old 06-22-2007, 01:36 PM   #2
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That's beautiful. I'm getting a little tear in my eye.

I like having a +1 everywhere. I might leave a little patch down near idle at the stock level so it idles nicely, and leave wide open throttle at stock as well.

To me, the place where I would want to be lean is at lower throttle openings, and middle rpms. Kind of a lean patch in the place where I spend my cruising time.

What kind of indicators will you have that you have gone too far? Are there temperatures that you can monitor? I would not want for pinging to be my only warning sign...
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Old 06-22-2007, 01:58 PM   #3
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If my daughter didn't need braces and the backyard relandscaped, etc, etc, I would have the Megasquirt for my CRX HF. But any way . . .

Considering that is an 8x8 table, I'm assuming that is an MSI, not an MSII. I'm not sure if an MSI will do this, but an MSII will allow you to set a target AFR ratio in closed loop. It also allows you to set a throttle or map sensor setting when to change to open loop. What I was going to do was set a lean closed loop ARF and a low throttle setting where it would shift to open loop. This would allow the car to run in a "lean burn" setting at low throttle settings, then when you hit a hill or need to accelerate, the car would go into open loop where the tables take over.

I'm also planning on getting an exhaust temp guage to monitor the exhaust temperatures and compare these to the stock ECU. This would also allow tuning the ignition advance in an attempt to keep the exhaust temps down as the car gets leaner.

Water injection is not a bad idea, but since most of these systems are designed for turbo engines when they are at boost, it might take a little enginuity to get a system that can supply what little water a small N/A engine at 1500-2000 rpm would need.
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Old 06-22-2007, 03:32 PM   #4
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Since I have the wideband it will always maintain target AFR so I don't have to worry about open/closed loop settings. If I want lean burn somewhere I can just set it in the table and it will do it

I am running the megasquirt and spark hires software. The regular ms&s didn't have enough resolution on the injectors at idle to adjust it properly. So far I have it idling dead perfect at up to 15:1 but I am thinking I might be better off waiting and adding an exhaust temp gauge to the car before I try for the super lean running. I am probably just going to add +1 to everything below 67Kpa and maybe go 16:1 at 28-3600 at 15Kpa
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Old 06-22-2007, 06:40 PM   #5
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Well I decided to play it safe and not really get carried away with the AFR just yet.



Hopefully that won't melt the pistons
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