Calculating A/F Ratio from precat O2 sensor
 

Hi, I was wondering if anyone knowledgeable can help me with this question.

Background: My stock 02 Protege ES seems to be running really rich at WOT. It seems to be just dumping fuel, especially more so after installing an aftermarket intake. I'm about to A/F tune my RX-8, but I wanted some experience with my beloved Protege first. So I got an OBDII scan tool to really see how rich my car is running. It turns out the scan tool only picks up the voltage from the two O2 sensors. I tried looking around for an equivalence ratio (lambda) multiplier for the precat O2 sensor voltage readings with no luck.

Question: Can someone tell me how I can convert the precat O2 sensor voltage into lambda or A/F ratio?

Thanks in advance!

honestly that narrowband 02 isnt worth crap at calculating a/f ratios....it isnt very accurate

macdaddyslomo,
I appreciate the frank answer.
So how are folks doing the ECU tuning? Replace the current sensor with a wideband sensor (is that compatible with the stock ECU)? Or drill another hole and stick in a wideband sensor next to the stock sensor and attach this to a voltmeter or AFmeter?

they arent tuning at all with the stock ECU...it's next to impossible...with aftermarket ECU's they are using a wideband or an EGT gauge to tune

Ah~ I see.
So even open loop tuning is tough, huh?
Thanks so much for the info. I sincerely appreciate it.

yes. the Mazda ECU's are practically un-hackable...to do any tuning you would need a full aftermarket controller, like a Haltech E6K