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Dudeland

My baby loves being rich.

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I have searched, and I cannot come up with a reason why my motor will only idle rich.  I converted it from carb to a Holley EFI, but both setups only worked if my idle AFR is at 12.5 or lower at idle. Completely different instrumentation in both cases, so I tend to believe the numbers.   

 

Also the bonus question for keeners

 

Why when I set an AFR target of 13.5 it will struggle to get to 12.5, and when I set it at 12.5, it struggles to get to 12. 

 

Is my cam off by a tooth?   It isn't burning oil, but the P.O f'd with everything. Maybe wrong pistons. I am looking for any guidance. 

 

 

 

 

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This may or may NOT be relevant to your mixture issues, but I've been using an AFR gauge / wideband O2 sensor set-up on my tii and have found that the ideal idle mixture based upon summer formulation fuel is 12.9 for my own car (10:1 Mahles, bone stock injection, valves at .007", timing roughly at 6-8 deg BTDC @850 rpm - I forget honestly, as I only worry about maximum advance numbers at 32-33 BTDC / 3500 rpm usually). Any leaner and I get the classic "tii surging idle". It seems happy as a clam at 12.9 and any leaner causes a wee bit of hesitation off-idle as well. 

 

Unless I have some other issue or cause to drive myself batshit crazy, I'm content to blame it on modern Ethanol fuel vs 1972 fuel formulations. At 12.9 the exhaust isn't eye burning or terribly obnoxious and my cruising AFR is about 13.9 with WOT at 5000 rpm at around 12.8 or so - which makes me happy. 

 

What is your ignition timing at idle - or for that matter, at 4000 rpm? That'll affect mixture for sure!

 

With that said, I have witnessed quite a difference with winter blend fuels here in the wilds of Pennsylvania, two months ago - where my AFR leaned out considerably during a 4 hour road trip. Bumped up at least 2+ whole points. I'm not going to mess with it again till the summer fuels are back and the road salt is gone. YMMV!

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Granted I'm carb'd DCOE, but Brunhilde also idles best at around 12.5ish, any leaner and it roughens up and affects the idle transition. 

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12.5 doesn't sound too rich for M10 idle; I think I usually run somewhere between 12.5 and 13.0 idling, and anything above 13 it starts to get rough.  Remember ignition timing also has a large effect on idle too, aim for mid-teens, and try to verify with a timing light.  (Your 123 still at 12 degrees at idle?) Lastly, it's easy to check the cam timing, just pop off the valve cover, line things up at Cyl#1 TDC, and make sure the little notch on the cam sprocket flange lines up:

 

I really think though it's pretty tough to get the timing chain off by a whole link and drive the car around without realizing something's wrong. . . so I doubt this is your issue.  But easy enough to check!

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Wow!  this is great news.  So I am not that far off at 12.5 (ish).  I figured with better metering and computer control it would idle in the mid 13's.  I do get it surging if I go to lean.  I tried to tune it out, but no go.  My timing is at 8-10 degrees at idle.  Now that I am in the ballpark,  I will push and pull around the timing and fine tune the mixture, but I think  I am going to see some light at the end of the tunnel.

 

Right now I am trying out an unconventional tuning method for the Holley.  Basically, you clamp down on CL compensation and learning,  close off the IAC valve and get it working kinda like a glorified carb,  tune your idle with the adjustment screw, bring your AFR in range, then take the tape off the hole going to your IAC and sort out the  cold start high idle and start mixture. 

 

It just may work after all. 

 

Regards 

 

 

 

 

 

 

 

 

 

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(edited)
49 minutes ago, Dudeland said:

Basically, you clamp down on CL compensation and learning,  close off the IAC valve and get it working kinda like a glorified carb,  tune your idle with the adjustment screw, bring your AFR in range, then take the tape off the hole going to your IAC and sort out the  cold start high idle and start mixture. 

 

Everybody else's system is tuned that way. You are doing good.  The hot idle should be where you want it without much if any help from the IAC.   IAC is there for cold engine/oil condition idle speed control.

 

On the subject of your idle A/F - if you have the capability to disable (turn off) the O2 correction loop at idle speed  (just above idle) and tune for best idle smoothness, it may help.  What usually happens is the A/F feedback control loop is fast and the injector gets a command to change the fuel amount.  At idle it takes time for the changed fuel amount to make it's way to the cylinder, be combusted and the gas to reach the O2 sensor.  The time for the sensor to see the change is longer where the injector is farther from the intake port as with the Holley on the long runner manifold.  So the control loop might be making more correction before the first change is sensed.  This delay and over reaction of the control loop happens at idle when very little air is used.  At higher loads all can be fine.  I'd say to give it a try, you can always revert to O2 control at idle.  Also some systems allow the PID control or sample rate time to be changed at low speeds to slow down the control loop response time.

Edited by jimk

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I **LOVE** this! Between old weirdos like me, and their 1840s technology / mechanical injection  (*wink*)  and the cool wave folks brave enough to jump in to high tech injection control (I'm too skeer'd), we may just get this fella where he needs to be! 

 

 

Keep us posted!

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On 1/10/2019 at 9:46 AM, jimk said:

Everybody else's system is tuned that way. You are doing good.  The hot idle should be where you want it without much if any help from the IAC.   IAC is there for cold engine/oil condition idle speed control.

 

On the subject of your idle A/F - if you have the capability to disable (turn off) the O2 correction loop at idle speed  (just above idle) and tune for best idle smoothness, it may help.  What usually happens is the A/F feedback control loop is fast and the injector gets a command to change the fuel amount.  At idle it takes time for the changed fuel amount to make it's way to the cylinder, be combusted and the gas to reach the O2 sensor.  The time for the sensor to see the change is longer where the injector is farther from the intake port as with the Holley on the long runner manifold.  So the control loop might be making more correction before the first change is sensed.  This delay and over reaction of the control loop happens at idle when very little air is used.  At higher loads all can be fine.  I'd say to give it a try, you can always revert to O2 control at idle.  Also some systems allow the PID control or sample rate time to be changed at low speeds to slow down the control loop response time.

I had the closed loop gated to 1300 RPM.   With the most recent tune, I don't need to.  I have it pinned down to 2% change, and that seems to help smooth out the idle.  The balance of the tune not at idle is at 5%,  we will see how it goes.  This is something that I will keep my eye on. 

 

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The more you drive it, the better the tune will become.  The correction map will go almost to zero changes (until you decide to change something in the air/exhaust system, then it will fix things again)

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It is more than eager to learn.  I have been holding it back. 

 

1) It seemed for a while that it wouldn't or couldn't meet the target afr's 

2) I was having a problem it overshooting the idle. 

 

Now that I am throwing more fuel at it, both seem to be under control.  I will drive it for a while before any other changes are made. 

 

Take a look at my blog comment today and let me know what you think. 

 

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I love the fact that hotrodding has evolved the way it has. What former WWII bomber pilots were doing with cars in the 50s, using aircraft parts, YOU GUYS are now doing using computers and sensors.

 

That.Is.So.Cool. 

 

Much of it is alien and a completely different language to me, but it's fascinating. 

 

*goes and hugs the springs inside his distributor*

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