tveltman

Okay, first things first: I know AFR gauges are vital, no dispute there. However, it seems to me that what you care about is an AFR gauge that tells you when the car is *consistently* running lean (like over a period of a few seconds or more), not one that gives you the instantaneous AFR. You would have to watch it like a hawk to get anything useful out of it. So my question is this: what sort of time scale do you think you could get away with to take the average AFR and still have it be meaningful with respect to the workings of the car. It seems to me that if you took the average AFR over the course of two or three seconds, you would still find consistent lean/rich conditions, but you wouldnt have to stare at a whole crapload of noise. Does the list think this is valid?

EDIT: I think you could average over as little time as a half second and you would still debounce the signal without degraded performance

danglerb

Without tracking rpm at the same time, load, etc. all you get from an AFR meter is a fancy warning light thats fun to watch, not really a tuning tool.

mark kibort

its not the lean that kills the motors, its the running the motor at Stoich. (14.7:1) however, if you are normally running WOTat 12.5 and suddenly you see you are at 17:1, what you worry about is what happened if it passed through 15:1 fairly slowly. as you say, very hard, if not impossible to tell. the engine can be damaged in a few seconds and possibly even shorter. so, the gauges are really for seeing if you have a problem with mixture.you could never follow one,expecially when you are WOT, you are too busy driving .However, on the track, if I dont see the bright blue lights of 12:1, i might just pull over and check. They are really a tuning tool, and not much more.

ptuomov

Here's a related question: Is lean condition (defined as the hottest burning mixture, not literally leanest) a real threat except when the car is running WOT (and/or with boost)?

I've been thinking about various alert conditions, and if I simply make the system sound an alert every time the mixture is lean, the car will start sounding like my BMW which always has some sort of warning sound coming from it, if for no other reason because it's out of gas.

I was thinking that I'd only trigger an alert condition if both WOT switch is on and the mixture is lean. Both need smoothing, both signals sent thru an ewma filter, say with a 1/4 second half life. I've never done anything like this before, wondering if this makes sense.

tveltman

Well, what I was thinking about was modifying the integrated boost gauge in the integrated 944 tach to read AFR instead. Basically I could use the same microcontroller (or an additional one to save computation time) to monitor the MAP sensor and calculate AFR, and translate the signal to 0-5V for the boost gauge. Then simply have a switch which the microcontroller would recognize, and then you could toggle between boost and AFR, and then remap the gauge face for AFR as well. You could even implement an idiot light so that if you were in boost mode and the AFR went wonky, the light would turn on. I think that it would be a very simple implementation, the trouble is what level of resolution is acceptable. For tuning, I would definitely use a digital meter, but for those that keep the AFR gauge on all the time, that would seem to be an attractive option. Hell, you could even delete the boost portion and switch it over to an "analog" AFR gauge, for those interested.

mark kibort

I dont think you care about mixture under any other condition, but WOT and down to 75% throttle max.
after all, at any other condition you are trying to get the most complete burn possible, and that is at Stoich. actually, going even leaner in those conditions gives better fuel mileage with no ill effects, actually, cooler EGTs and CHTs too. (just before the engine starts running poorly)

so, you would care about lean or going leaner than what it should be, and an alarm that buzzes, or a light that goes off under 75% full throttle condition and higher, when things start to go lean, is not a bad idea. I think a light that goes on when the knock sensors are being hit would be best.! Hey, there is an idea!!!

AO

I have a couple AFR gauges. When I'm tuning, I pulg in my Innovate XD-16 which I can program to display a few different monitored parameters. When using it fro AFR, I can set alarms if it goes beyond certain ranges. So let's say I'm at WOT, and AFR goes leaner than 14.0 it blink like crazy. Hard to ignore that.

I know some guys who have it mounted as their permanent AFR gauge, but I have a digital gauge that I use as my regular gauge.

I highly suggest you check our Innvate Motor Sports. They have a pretty good forum where you can get a lot of additional information.

danglerb

Peak EGT is at stoichiometric isn't it?

zoltan944

AFR can also help in diagnosing problems. Ive had 2 fuel pumps go bad that I already knew was more than likely fuel pumps by the gauge, confirmed by the fuel pressure gauge under the hood.
Those that have em can use them for diagnosis as well as tuning.
Yes 'lean condition' is sort of a mislabel as this is a condition that allows the motor to run and break.