Cobb AP: AFR range?

[08MicaMS3]

What's the accurate range of the onboard oxygen sensor? I think something is up with my Cobb AP readout- the data log shows multiple times where my AFR is as high as "29.25".

Seconds (sec) RPM (RPM) Knock Retard () Throttle Position (%) Vehicle Speed (mph) Actual AFR (AFR) Boost (PSI) Spark Adv. ()

75.34 2294 0 3.9 27.96 29.25 -11.75 10

Normally I thought AFR ranges were limited to as low as 9.0 (some sensors) to as high as 17-20.0 (some sensors).

Is this a fluke or a real number?

 

[ReNaToMS3]

Your car is gonna blow-up!


Nah, just kidding. Once you let off the throttle, the injectors are shut off, otherwise you would keep accelerating. It takes fuel outta the mixture. All normal.

 

[8.5MS3]

AAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHHH

your fine. the injectors close during overrun, so no fuel is injected, hence, afr goes to infinity, but the scale ends at 30

 

[08MicaMS3]

Your car is gonna blow-up!


Nah, just kidding. Once you let off the throttle, the injectors are shut off, otherwise you would keep accelerating. It takes fuel outta the mixture. All normal.

I understand how that works, what I'm saying is I don't understand how it would show a 29.25. Is the range on the OEM sensor that large? Every aftermarket sensor and so on only makes a distinction between 10.0:1 to 17.0:1. That's what I'm referring to. I know that off the throttle fuel cuts out... does anyone know the real range of the sensor? (How rich and lean it can sense?)

See the attachment:

 

[8.5MS3]

AAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHHH

your fine. the injectors close during overrun, so no fuel is injected, hence, afr goes to infinity, but the scale ends at 30

 

[08MicaMS3]

but the scale ends at 30

Where's it say that, and where do you get that information from?

 

[8.5MS3]

i have the mazdaspeed3 tech manual

 

[08MicaMS3]

i have the mazdaspeed3 tech manual

Thanks. Nice pickup BTW, what's something like that cost? I assume you have the hard copy?

So apparently with the DISI, the AFR sensor is just extremely sensitive... I gather

 

[8.5MS3]

Thanks. Nice pickup BTW, what's something like that cost? I assume you have the hard copy?

So apparently with the DISI, the AFR sensor is just extremely sensitive... I gather

i have both (hard and electronic), i got mine off a local who sold his MS3 for free. typically they sell for 75 bucks or somewhere around there.

yes the sensor is extremely sensitive, it has to be with DI since the car is running on the brink of knock all the time

 

[hugador]

i have both (hard and electronic), i got mine off a local who sold his MS3 for free. typically they sell for 75 bucks or somewhere around there.

yes the sensor is extremely sensitive, it has to be with DI since the car is running on the brink of knock all the time

+1 I don't have an aftermarket rmm so when I don't do a smooth shift and the car buckles, I will see KR.

 

[matsuda]

I understand how that works, what I'm saying is I don't understand how it would show a 29.25.

1) The AFR reading is derived from a standard "OBD" PID for equivalence ratio (lambda).

2) A lambda value of 1.00 = stoich (14.64:1 AFR).

3) According to the OBD spec, the ECU gives a 16 bit value (0~65535) for lambda. which corresponds to a lambda value of 0~1.999.

4) When the injectors are shut off, the ECU will report that the lambda is 1.999 (the maximum value), when in fact it is infinity.

5) 14.64 * 1.999 = 29.26