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Old 04-06-2010, 05:25 PM   #21
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I don't want to come across as a fear monger, but idling at 17:1 is likely producing significant amounts of NOx and poisoning us all.

get your car idling between 14.3 and 15 AFR.

though I also have to wonder if you're really idling at 17:1 due to the inability of the wideband to measure at low gas volume flow rates. anyone ever check it with a narrow band?
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Old 04-06-2010, 06:37 PM   #22
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AFAIK cars are basically designed to idle at around stoich or a tad leaner. Certanly wont hurt anything.

I always found that richening things up a bit made for a smooth idle, but other than maybe a slight change in perceived NVH, no reason to run it rich at idle. I cant beleive people are ideling at 13:1. Dont most OEMs try to run like 20+ degrees of timinmg at idle too? Its much more efficient to run at stoich with around 20 degrees advance in term of fuel consumption. Your best efficiency in just about any situation is when your peak cylinder pressure is at 14 degrees ATDC. So running the minimum amount of fuel to keep the enigne turning at say 900RPM by using that timing is the way to go.

Y8s has a good point too. I wonder if a narrow band reading would be like .75V in this case.
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Old 04-06-2010, 06:40 PM   #23
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this eeeeprom of the stock 1.8L timing suggests it idles at 10*

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Old 04-06-2010, 06:43 PM   #24
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Wait...what is load in? Inches vacuum?
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Old 04-06-2010, 06:48 PM   #25
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Quote:
Originally Posted by Sparetire View Post
AFAIK cars are basically designed to idle at around stoich or a tad leaner. Certanly wont hurt anything.

I always found that richening things up a bit made for a smooth idle, but other than maybe a slight change in perceived NVH, no reason to run it rich at idle. I cant beleive people are ideling at 13:1. Dont most OEMs try to run like 20+ degrees of timinmg at idle too? Its much more efficient to run at stoich with around 20 degrees advance in term of fuel consumption. Your best efficiency in just about any situation is when your peak cylinder pressure is at 14 degrees ATDC. So running the minimum amount of fuel to keep the enigne turning at say 900RPM by using that timing is the way to go.

Y8s has a good point too. I wonder if a narrow band reading would be like .75V in this case.
I've played around with my OBD-II scanner/live data tool on a few late model cars (Jeep GC, BMW) to look at "factory idle". Startup is open loop, then cars go to closed loop in under a minute. Ignition timing is "dithered" up & down (delta can be as high as 10 degrees at idle) to maintain target idle speed within about 25 RPM. If you can get a boosted Miata to idle smooth at stoich, there is no reason to go any richer. As Y8s notes, going leaner than stoich (some combinations will idle OK leaner than stoich) is problematic because it significantly raises emissions levels and will save very little fuel.

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Old 04-06-2010, 06:50 PM   #26
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Huh. You learn something every day. Good to know that they start in open loop. Makes sense I guess since the sensor is not really ready to go untill it heats up. They must run those heater elements in order to get them to closed loop sooner for emmisions.

The map looks like Mt. Fuji. Except not really.

I think it would be baddass to design a setup such that the fuel or spark map looks like Elvis or something. But you would need some really good resolution in your mapping to do that.
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Old 04-06-2010, 07:18 PM   #27
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you guys are crazy idleing below 13:1. way too rich, besides washing the cylinder walls down with fuel, the unburned gas is contaminating you oil prematurely. smell you dipstick, does it smell like gas? not good. my car idles great between 15-16:1 afr. 14.7-15.2 is the norm for stock vehicles. (that's the range of the narrow band o2 sensor usually also)

best compromise at wot when i run trackdays is 11.7-11.8 afr. 11.5 and below is too rich, power loss and and low mpg are not necessary.
above 12.0 doesn't leave any safety cushion.
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Old 04-06-2010, 07:46 PM   #28
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Brain,

Is that 1.8 map from an OBD-I or OBD-II car??
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Old 04-06-2010, 09:16 PM   #29
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After a fresh start this afternoon I made some progress. Found out that my IAC was sticking open and even though it allowed me to idle leaner than usual it created other issues. It now idles in the high 13s with no load and it rises to mid 14s when the fan kicks on. This is at just over 1000 rpm and is about the smoothest it has ever been with 16* of timing. I think I'll leave it like this for now.
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Old 04-06-2010, 11:00 PM   #30
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On my old VE table and spark table my car used to surge a little at idle and run in the 13's and 10* spark 800ish rpm. Now after getting my maps straightened out it idles pretty darn smooth at 14.5-15 afr 19* spark and 1000rpm
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Old 04-29-2010, 06:06 PM   #31
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I'd also like to know what the load axis relates too 0-15?

Brain?
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