SMasterson

When I have my bin file constants set to 14.50 in the 'Stoichiometeric Air Fuel Ratio' in Tunercat anytime I wasn't in PE mode and while scanning my engine with the beta version of Datamaster it almost always reports the a/f ration as 14.50.

If I change the constant to 14.69, burn another chip and scan with Datamaster it almost always reports it as 14.69. Exceptions are when i PE mode, or heavy decel. All cruise a/f ratios are reported as whatever I set in Tunercat.

I find this odd, unless the commanded a/f ration is included in the data stream somewhere, which I did't think it was.

What I find odd about this is I didn't think the O2 sensor was that accurate. Is it just a fucntion of the ECM doing the math to report a resulting number, or does it know before it calculates it what the a/f ratio is supposed to be?

Any help understanding this is appreciated! I'm actually having a hard time tying to figure out how to word this question.

BTW, I'm using a '730 SD ECM with a heated O2 sensor in the header collector.

Thanks, in advance. . .

Grumpy

It's commanded AFR.
Not actual.

Commanded is what the AFR averages out to. The ecm toggles across Stoich, it goes rich and lean, to keep the converter working properly.

SMasterson

I understand that. What I don't understand is if Datamaster is calculating that value from the data it's receiving from the ECM through the sensor, pulse widths, etc., or does it have a way of actually knowing what value is set in the PROM?

Maybe another way to ask is; Is that the value is *supposed* to average out to, or the value it actually *is* averaging out to?

Here's what I'm talking about:

RBob

iTrader: (1)

The commanded AFR is sent out the ALDL as one of the datastream parameters. This is what is being displayed.

RBob.

scorp508

Be happy you can see it!! I use EASE and it does not display commanded AFR. Oh well <shrugs>

What ECM are you editing that gives you the ability to set that in Tunercat?

SMasterson

That's the conclusion I came to but wanted to verify it. There are just too many variables going on for that value to remain as steady as it does. I looked through the basic code of CM's data logging program but still didn't find what I was looking for.

BTW, the beta version of Datamaster 8D shows this value. The 3.4.1 version show a number of about 470 instead of 14.??.

I don't ask too many questions since most can be answered with a *Search* but this one had me stumped.

Thanks a lot,