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Old 07-25-2000, 12:18 AM   #1
Scooby Specialist
Member#: 80
Join Date: Jul 1999
Post O2 sensor readings for MY99s

Hi guys,

I finally got a Jumptronix A/F meter installed in my car during NESIC's recent garage day. It's hooked up to my first O2 sensor (this is a NA MY99 with intake&exhaust) After watching it dance around for the past couple of days, I've got the following observations/questions:

* boy, it dances around a *lot*. The only time it settles down to a value is at WOT. Is the sensor noisy or something? Or is this normal? I admit I don't know much about what the O2 sensor is for.

* I've done some searching and found that people are seeing readings around 0.8v at WOT. I'm reading 0.86 to be exact. Are the others out there just using gauges that can't show more accurate readings (down to hundreths of a volt), or do I really have a different reading than other people?

* what readings should I be worried about? 0.6V? 0.5V? I intend to eventually turbo the car, hence my having the meter in the first place.

* does turbocharging the engine change O2 readings?

Thanks in advance!

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Old 07-25-2000, 12:24 AM   #2
Eric SS
Sooby Guru
Member#: 1914
Join Date: Jul 2000
Chapter/Region: SWIC
Location: 2014 Q60S, 2016 Chevy SS
2000 2.5RS w/ EJ22T
swap and N20. gone. : (


To be perfectly honest bud, unless you get a Wideband O2 sensor, your A/F ratio meter is pretty much worthless, especially at wide open throttle. Shortband O2 sensors can't read O2 counts under WOT very good at all. I would be very cautious of tuning your car from what your O2 sensor tells you. Just my $.02

MY00 Aspen White
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Old 07-25-2000, 12:27 AM   #3
Scooby Specialist
Member#: 607
Join Date: Dec 1999
Location: SF Bay Area, CA


The voltage will jump around a lot. This is called closed loop. The only time it will go open loop (no jumping) is during cold start, high rpm, or WOT. During closed loop behavior, the ECU is constant trying to "zero in" on the desired a/f ratio targets.

The voltages coming from your narrow band o2 sensor aren't exceptionally accurate for a/f ratios above or below 14.7:1 but .86v sounds good for WOT. If it gets much lower, you are experiencing lean run.

Turbocharging will affect o2 readings in a big way. Hence, the importance of good fuel (and ignition) management.

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Old 07-25-2000, 07:05 AM   #4
Scooby Specialist
Member#: 80
Join Date: Jul 1999

Oh, I definitely plan on having more instrumentation than just a A/F meter to tune my car. I just wanted to understand the readings I'm seeing. Thanks for the info.

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