Lean idle question
 

Is it possible to be too lean at idle? I've always maintained an idle in the high 12s at around 1100 rpms with RC 750cc injectors and it would occasionally flip out when the fan would come on. Just never spent the time to get it right. That is until yesterday, I started to lean it out a bit and got the best idle with an afr of 17-18 at 900 rpms with my 750cc injectors. The fan would come on and it wouldn't flip out or anything. Since there isn't much load on the engine, I wouldn't think it would be a problem, but I would rather ask then risk damage.

You're not going to cause damage to the engine at idle.

However, i'm surprised to shit that your car idles that lean. My car idles best at 13.3:1. Anything over 14 it starts poppin and spittin. Does your car run lean overall?

I usually like to keep it pretty rich overall, but I've been experimenting a bit lately. Did some pulls yesterday at 19# and had it as lean as 12.0 while I was getting it dialed in just to see the change in my injector duty cycle. It's back down to 11.5 now. I also finally installed a wideband, besides the one that the Hydra uses. Since idle and cruise is about the only time I will actually look at that thing I figured this would be a good place to start.

Hmm. When my car idles smoothly with numbers like that I know I have an exhaust leak letting air in thus giving me lean AFR numbers.

If it works for you that lean i'd say run it.

With 750cc injectors, my car is pretty happy at 13:1 at 750rpm right now. I might go down to 12:1 if I can't get some idle stalling problems fixed, but I don't realize any more benefit going below that.

Like Wayne said, that's amazing it will idle that lean.

The sensor on the Hydra isn't the best at low flow rates, so I'm going by what the plx sensor is telling me. I'll put in the spare sensor and see if it does anything different. I did also just change out the exhaust cam, not sure if it would affect things much, it's pretty mild.

Are you idling open or closed loop?

Open loop at idle, after 1500 I go closed loop. Even the Hydra gauge says I'm over 16.

I idle best in the 14.5:1 range, but no issues at 15.5:1

wooooooah
you guys are idling rich as fuck

I usually try to get the idle AFRs down into the 16s and 17s, occasionally it will have to be a little richer if its unstable that lean, but its usually no problem at all.

What spark timing are you guys running at idle?

15-17* something like that.

You guys are all over the map.

My car pretty well hates anything below 13:1 at idle, or over 16:1. Mine is always changing though, I need to figure out how to keep MLV from changing those cells.

welcome to the club. My car did exactly teh same shit. still can't figure out how to fix it.

In fact I made a thread EXACTLY like this a little while back. almost word for word lol

I fixed my idle issues. 14* timing, AFR reads 14.3-14.8 at 750-800 RPM in closed loop

440CC RC injectors.
HydraEMS 2.6

you can't figure out how to select: Min RPM & Max RPM?

Set the min RPM Noob!

Edit: should have kept reading.

I'm going back to a virgin map this afternoon to play around and see what happens.

I idle pretty okay at 17.5:1... no issues.

Just found all this, thanks for prompting me to look.

http://www.ideasandsolutions.biz/Meg...eAnalysis.html

Third of the way down this page, apparently I need to "Show Advanced Settings" :idea:

Rock on!

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?

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.

this eeeeprom of the stock 1.8L timing suggests it idles at 10*

http://www.boostedmiata.com/gallery2...ck18timing.JPG

Wait...what is load in? Inches vacuum?

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.

.

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.

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.

Brain,

Is that 1.8 map from an OBD-I or OBD-II car??

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.

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

I'd also like to know what the load axis relates too 0-15?

Brain?