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Old 04-06-2010, 02:20 PM   #1
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Default 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.
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Old 04-06-2010, 02:30 PM   #2
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You're not going to cause damage to the engine at idle.

However, i'm surprised to **** 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?
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Old 04-06-2010, 02:36 PM   #3
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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.
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Old 04-06-2010, 02:38 PM   #4
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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.
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Old 04-06-2010, 02:39 PM   #5
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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.
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Old 04-06-2010, 02:44 PM   #6
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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.
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Old 04-06-2010, 02:46 PM   #7
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Are you idling open or closed loop?
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Old 04-06-2010, 02:48 PM   #8
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Open loop at idle, after 1500 I go closed loop. Even the Hydra gauge says I'm over 16.
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Old 04-06-2010, 02:51 PM   #9
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I idle best in the 14.5:1 range, but no issues at 15.5:1
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Old 04-06-2010, 02:54 PM   #10
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wooooooah
you guys are idling rich as ****

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.
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Old 04-06-2010, 02:56 PM   #11
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What spark timing are you guys running at idle?
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Old 04-06-2010, 03:04 PM   #12
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15-17* something like that.
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Old 04-06-2010, 03:27 PM   #13
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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.
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Old 04-06-2010, 03:28 PM   #14
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welcome to the club. My car did exactly teh same ****. 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
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Old 04-06-2010, 03:33 PM   #15
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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
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Old 04-06-2010, 03:34 PM   #16
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you can't figure out how to select: Min RPM & Max RPM?
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Old 04-06-2010, 03:40 PM   #17
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Quote:
Originally Posted by gospeed81 View Post
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.
Set the min RPM Noob!

Edit: should have kept reading.

Quote:
Originally Posted by Braineack View Post
you can't figure out how to select: Min RPM & Max RPM?
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Old 04-06-2010, 04:47 PM   #18
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I'm going back to a virgin map this afternoon to play around and see what happens.
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Old 04-06-2010, 04:55 PM   #19
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I idle pretty okay at 17.5:1... no issues.
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Old 04-06-2010, 05:18 PM   #20
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Quote:
Originally Posted by Braineack View Post
you can't figure out how to select: Min RPM & Max RPM?
Quote:
Originally Posted by wayne_curr View Post
Set the min RPM Noob!

Edit: should have kept reading.
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"

Rock on!
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