Bad30th

iTrader: (13)

"How lean is too lean" ? From what I've read it's subjective to RPM, load and ECT, correct ? (Oh, and please consider I'm FI, but let's also discuss N/A).

What AFR would cause mechanical damage at idle ? What about part throttle ?

What about under load, does that change the AFR requirements at lower RPMs ? Obviously fuel economy comes into play but I'm more concerned about hurting something mechanically while tuning...

Stoich or close to it should be fine at any RPM up to close to WOT at a low load, right ?

Most of the time when we talk about AFR it's WOT AFR, and everyone has a pretty good idea of what lean/rich is for their particular WOT application, but I can't find much info on what to command/dialing in AFR for idle and part throttle.

I'm asking because my startup AFR is wandering pretty good (sometimes into the 16's-17's) but it seems OK and idles fine. Once it's warmed up the AFR is getting very close to commanded (I'm still tuning VE in SD). Hope to turn the MAF back on tomorrow and start logging AFR error % to dial in the MAF table.

Thanks,
Rob (Bad30th)

horist

13.0:1 w/no KR is as lean as I would go on an NA application... people have run leaner than this (some i've seen go as lean as 15.0:1) w/out blowing hte car up... but it's just a matter of time if the AFR is that lean

Plus ... lean = power to a certain extent... 12.8-13.0 seem to be ideal for max power


(above is WOT)

For part throttle... I believe something like 15.4:1 is ideal for fuel economy (but not for emissions) ... any leaner and it's not helping any


do you still have your AIR Pump and/or EGR enabled? If so that could be causing false lean conditions during startup I believe....

Bad30th

iTrader: (13)

I do still have AIR and EGR and I thought of that. The wandering AFR happens on warm/hot starts too - doesn't the air pump only run on cold starts (or could that be it ?).

I am also just interested in learning how lean or rich is 'bad' and mechanically what can happen - I know at low load/low RPM cruise like you said you can save fuel economy by having a lean AFR (up to say 16 or so) but that same 16:1 AFR would blow my stock pistons in my FI engine to bits at WOT. That's kind of the gist of what I'm wanting to discuss...

Thanks !
Rob (Bad30th)

Dave F

you will not hurt your car running lean at idle or low-throttle driving, unless you have horrible knock. There is not enough fuel, ie heat, to do any damage at low-load.

technical

The comparison is not AFR vs. RPM, but AFR vs. Load or MAP. Even at high rpms you can run lean with no damage. As load increases AFR should richen.

Bad30th

iTrader: (13)

This is exactly the info I was looking for, and kind of what I was thinking when I made this post !

So, let's say 4000 RPM at 70kpa could be OK with 14.6:1, but when MAP/load increases to 105kpa, a safe AFR needs to be richer (let's say ~11.5:1 for FI, 12.8:1 for N/A) ?

Same goes for even idle RPM range, right ? 2000 RPM, 70kpa, 14.6:1 but 2000 RPM, 105kpa needs richer AFR as described above ?

It's all starting to make sense...

Thanks !
Rob (Bad30th)

WS6FirebirdTA00

iTrader: (33)

if you look at the g/cyl you get that can tell you more. high values here mean you want it to be richer, ie more load. looks like you are understanding from your last post. i run about 13.2:1 WOT, from waht i have seen 13.4:1 is the high limit on wot n/a. i heard the same thing that horist said about the afr for best power as well as best torque, but my car feels like a slug being rich like that, wont even break the tires loose on accel.

im curious on your startup issues you are having. didnt you say the olfa table was set to 1.00? im curious if timing corrections play a role in this as well as your air pump and egr. did you put your air enable temp very high? thats just odd...