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Old 07-16-2014, 02:13 PM   #1
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Default Let's discuss AFR safety system

MS3x gives the ability to have the engine cut fuel and / or spark if AFR is high by certain amount. Below is a picture of how it is set, with my settings:



In getting this set up, I discovered that I had inadaquate WUE as when I was at CLT of 165*F, and 90kPA, it would trigger.

I got that sorted out, but it caused me to think further into the pros and cons of this system. If you notice, fuel is killed until some action is taken (typically, lift the throttle). OK. But, if one is merging into traffic, hitting a good power, and this kicks in, we may be saving the engine, but causing a rear-end collision.

Even though it says no warning output, the CEL actually lights until raising the throttle resets the fault.

Who uses this? If so, why and how set. If not, why not?
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Old 07-16-2014, 02:19 PM   #2
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Wanted to use this on my prev ms3, never got around to it, in for results/feedback as I'm sure I'll be using it on my next MS

*edit: I wasn't even going to bother with the sub 120kpa rows because even if you were stoich it in those for a second or two you likely wouldn't damage things.
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Old 03-23-2015, 08:27 PM   #3
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Default Update

Update:

I'm not sure what I did, but I now no longer get the CEL warning. I do get a warning annunciator in TS, however.

Here is my latest set-up:


I moved the wait for from 0.4 to 1.0. This I did to stop transient triggers still.

These observations:
1) I can get lots of warnings, and an occasional trigger on the first hard pull of a run cycle. This is true even if I wait until things are fully warmed up. Then all subsequent pulls are no problem. I don't think this really has anything to do with this system, but rather some interesting tuning thing, like cold IM, that results in lean mixtures the first time in boost.
2) Occasionally I will (in TS) get the warning but no trigger, and the warning light will stay on until I accelerate again. It's like some of the UNTIL'S get hung up and hold the warning light on.

I'm not really sure that I'm using this correctly, and that perhaps I should set the timer to 5 seconds, so that only long term issues cause problems. Or possibly leave it short, but set the limits a little looser (not 0.3 up top).

Again, open to thoughts on the value / virtue of this system.

How many cycles of lean can an otherwise well tuned stock, boosted engine run before cylinder temps get high enough to begin knock? Is that known?

Oh, on my list is to hook up a LED to flash when warning takes place. When that is in place, it still makes sense to utilize this function with tight AFR settings, but long delay to fuel cut. It will also flash with knock sensed timing retard.

*EDIT: I just now saw Vlad's edit. Thanks, an input point. Effectively, I'm doing that with big error allowances.
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Old 03-23-2015, 09:08 PM   #4
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I'd like to run a restrictor rather than a thermostat and run a car on a dyno at a fixed load and rpm and watch egt and water temp as timing and AFR is changed.

In terms of a normal car on the street I imagine that a single gear pull at 20psi and 15:1 AFR would survive just fine with the presence of knock.

Dann

Last edited by nitrodann; 03-23-2015 at 09:38 PM.
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Old 03-23-2015, 09:25 PM   #5
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Quote:
Originally Posted by nitrodann View Post
I'd like to run a restrictor rather than a thermostat and run a car on a dyno at a fixed load and rpm and watch egt and water temp as timing and AFR is changed.

In terms of a normal car on the street I imagine that a single gear pull at 20psi and 15:1 AFR would survive just fine with the a sense of knock.

Dann
OK that would be info. What is the end of the last sentence supposed to say? I don't think it translated correctly.
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Old 03-23-2015, 09:38 PM   #6
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edited.
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