AFR lean at idle

[forwheeler]

I have an LM2 which I used to trace some runs. I don't have any rpm logging so you can't see everthing from this graph. It doesn't look too bad but it gets way
too lean at idle. The graph doesn't show the idle but only crusing in 2nd gear with one boost run. At idle it leans out to almost 17:1.

I assume that if I richen it some then the boosted afr will be too rich.

[DonE]

Don't worry about idle AFR. As long as it idles without missing or bucking, you're OK. At idle, you're not going to run into detonation - retarded timing, low RPM and low compression. As long as the AFR is good at 80 kpa to 200 kpa, you should be good.

[mark houghton]

For the idle, you can adjust the mixture at the fuel head, deflecting the control arm down just a hair (we're talking like a scant turn on the screw). That'll fix your idle and have just a very mininal effect on midrange and really no effect at all on boost. I adjusted mine last weekend after seeing my AFR's at 14.0 @ idle....I wanted closer to 14.7. Ended up with 14.4 (so now we're splitting hairs, I know). It did result in higher AFR's during steady no-load cruising (which is what I was after) but under load and on boost, no impact.

[forwheeler]

Originally Posted by mark houghton

For the idle, you can adjust the mixture at the fuel head, deflecting the control arm down just a hair (we're talking like a scant turn on the screw). That'll fix your idle and have just a very mininal effect on midrange and really no effect at all on boost. I adjusted mine last weekend after seeing my AFR's at 14.0 @ idle....I wanted closer to 14.7. Ended up with 14.4 (so now we're splitting hairs, I know). It did result in higher AFR's during steady no-load cruising (which is what I was after) but under load and on boost, no impact.

I am concerned about the 16+ afr at idle. 14.7 seems very good to me.
It does miss at idle so I want to richen it up some.
I don't know how to adjust the control arm unless it is the allen screw next to the fuel head that you turn clockwise to richen.

[beepbeep]

Are you using sniffer sensor mount? If you do, it will display lean even if AFR's are rich due to extensive "puffing" of gases out of tailpipe. It will draw in fresh air between all "puffs". When revs rise, it will flow more evenly so this error disappears.

[mark houghton]

Originally Posted by forwheeler

I am concerned about the 16+ afr at idle. 14.7 seems very good to me.
It does miss at idle so I want to richen it up some.
I don't know how to adjust the control arm unless it is the allen screw next to the fuel head that you turn clockwise to richen.

Here's a thread on the topic:

mixture control

Reach back across the top of the air cleaner assembly, back to the fuel head. Depending on what year your car is, there should be a spring-loaded post that you can turn with your fingers, but it won't do anything unless you first depress it to "engage" it with the adjusting screw inside the head. You need an allen wrench to turn it once it's depressed (you'll feel it engage). Turn clockwise to richen just a small amount (like less than 1/8 turn to start with). Depending on where your wideband O2 sensor is located, you may or may not get accurate idle CO readings at idle.

[forwheeler]

Originally Posted by beepbeep

Are you using sniffer sensor mount? If you do, it will display lean even if AFR's are rich due to extensive "puffing" of gases out of tailpipe. It will draw in fresh air between all "puffs". When revs rise, it will flow more evenly so this error disappears.

I am clamping it to the tailpipe with my own home made mount and it puts it inside about 11". It was poping during idle so that seems too lean to me.

[forwheeler]

Originally Posted by mark houghton

Here's a thread on the topic:

mixture control

Reach back across the top of the air cleaner assembly, back to the fuel head. Depending on what year your car is, there should be a spring-loaded post that you can turn with your fingers, but it won't do anything unless you first depress it to "engage" it with the adjusting screw inside the head. You need an allen wrench to turn it once it's depressed (you'll feel it engage). Turn clockwise to richen just a small amount (like less than 1/8 turn to start with). Depending on where your wideband O2 sensor is located, you may or may not get accurate idle CO readings at idle.

Yes that is where I adjust it so we are talking about same screw. Thanks.

[forwheeler]

Do I need to worry about changing the mixture with altitude changes or will the WUR compensate?

[beepbeep]

Originally Posted by forwheeler

I am clamping it to the tailpipe with my own home made mount and it puts it inside about 11". It was poping during idle so that seems too lean to me.

Sniffer pipe is known to be inaccurate and err on the lean side at idle. Thus I would only trust CO-meter when it comes to adjusting the idle CO.

[mark houghton]

I don't think the WUR is made to compensate for large swings in atmospheric pressure...such as from sea level to say 8000 feet, a peson may have to re-set the control pressures. And I would agree with Goran that probaby the best means of confirming your CO is with a CO tester. I use a Gunson and ram it up as far into the exhaust as I can.

My wideband O2 sensor for my cockpit AFR gauge is mounted even closer to the exhaust tip than yours (maybe 8 inches in), and it tends to read 16 AFR at idle...but it only takes raising the rpms up to maybe 1800 and they settle back to around 14.2. Just get some exhaust moving at a velocity above idle and you'll get hopefully a closer read to actual. Either way, it's all relative. If you make an adjustment to your idle mixture screw, you should see a relative change in the AFR's. In the absence of a CO tester, if your car is running a smooth idle and your eyes are not watering from being overly rich, then call it good.

[forwheeler]

I guess I need to check into a CO meter then. Thanks