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Old 03-01-2009, 12:01 AM   #1
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Default Lean off throttle

I think this is perfectly normal, but I just wanted to run it by you guys to make sure before I go spilling a soup of 10w30 and motor chunks all over the road. When I let off the throttle, engine breaking, coasting to a stop, my wideband reads full lean (AEM, I just get the "---"). I also get some occasional popping, it actually sounds a lot like every modded SRT4 on the planet

When I datalog and run the ve analyzer it keeps wanting to pull more fuel out in the lowest map row on the table. Is it doing what it's supposed to? Should I be reading ~14-16 AFRs when I'm in those cells or is being super lean acceptable since the motor isn't under any load at all?

I know it's a stupid question, but I just wanted to make sure I wasn't screwing something up. The rest of the map seems to be tuning in really well.
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Old 03-01-2009, 12:06 AM   #2
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Could be your over-run fuel cut coming on. It cuts fuel at max vac when you're off the gas. It's adjustable.

I personally disable it and tune my VE table to run the engine like normal in these cells. Improves driveability A LOT. I used to do overrun but not anymore.

Oh, and no it won't hurt it to run lean at light load.
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Old 03-01-2009, 12:07 AM   #3
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There are two ways you can create this event in MS.
Lean AFR values in the lowest row of your AFR target table.
Overrun Fuel Cut

If your AFR values are really low in the lowest row of your fuel table then MLV will tune for those low values.

Overrun fuel cut can be setup to only cut fuel when engine braking, I use this method.

It won't hurt anything. I prefer to have it tune for 15:1 in the bottom row where it would be engine braking but when I actually am engine braking Overrun fuel cut cuts in.
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Old 03-01-2009, 12:15 AM   #4
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Thanks for the quick replies. I think the targets for those cells are something around stoich so it must be the overrun fuel cut kicking in. Good to know I'm not doing any damage, at least in that respect.
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Old 03-01-2009, 12:24 AM   #5
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1) overrun = no fuel squirts (your **** is fine)
2) if you think the popping noise is crazy, ride in my car
3) who's tuning your car?
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Old 03-01-2009, 12:38 AM   #6
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I kinda like the popping, I think it appeals to my inner ricerness.

I'm tuning it myself so far, just using a conservative spark map and for the most part letting ve analyzer do the air-fuels. I don't think there's a tuner anywhere locally that I'd trust more than I trust more than myself, which is pretty sad.
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Old 03-01-2009, 01:09 AM   #7
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Think about how an engine works. It's a combustion driven air pump. But when there is no need for combustion, it is a rear wheel driven air pump. No need for combustion means no fuel. This is why it's better for economy to slow down in gear than in neutral. Saves brakes too.

Quote:
Originally Posted by cjernigan View Post
It won't hurt anything. I prefer to have it tune for 15:1 in the bottom row where it would be engine braking but when I actually am engine braking Overrun fuel cut cuts in.
Then you're wasting perfectly good resolution. Let overrun handle the off throttle fuel cut. Take back the bottom row to help smooth out idle or cruise lean or something.
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Old 03-01-2009, 02:41 AM   #8
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Pretty sure my lowest row is like 16 kpa, it's well utilized for realz. I use overrun to the fullest extent. I haven't even looked at my MSQ in.... 5 months. That's saying something.
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Old 03-01-2009, 11:55 AM   #9
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Quote:
Originally Posted by pdexta View Post
When I datalog and run the ve analyzer it keeps wanting to pull more fuel out in the lowest map row on the table. Is it doing what it's supposed to?
Within the VE Analyzer window, set the "Min MAP" to be equal to or just slightly lower than the lowest row in the VE table. This way. MLV will ignore data for MAP values less than that and it will stop doing ridiculous things to the bottom row.

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