michael2e

What is the actual O2 sensor voltage reading when in optimally tuned closed loop in your experience?

michael2e

Anybody? How about you guys with the SMT6? My research and trials suggests an optimal tuning results in 0.88 volts coming out of the O2 sensor during closed loop acceleration.

Bill

Optimally tuned during closed loop? This varries under operating conditions.

CONDITION

Part throttle cruzing under light load - The air/fuel mix should be optimal at 14.7 to 1. Your O2 signal will be 1.0 volts at 14.7 to 1.

Full throttle, heavy load - The A/F mix should be around 11.5/1. Your O2 signal will be around 0.8 volts.

Closed throttle, decelleration - The A/F mix will be around 21/1. The O2 signal will be around 1.5 volts.

The lower the O2 sensor voltage (.05) the richer the mixture. When you see low voltages, your O2 sensor is asking the engine management to lean out the mixture. Under full throttle/heavy loads/cold engine, the computer will ignore the O2. The higher the mixture (1.5) you have a lean mixture.

Jeremy Himsel

Please do not follow Bills advice, he is extremely misinformed about narrowband 02’s and if you tune based upon his direction you will pop a headgasket very quickly. Our O2 sensors operate on a 1V DC system so you should never see more then 1V. An output voltage of 0.2 V (200 mV) represents a really lean mixture, a reading of 0.8 V (800 mV) DC represents a ricehr mixture and stoich is about 0.45 V (450 mV) DC. Under load/boost shoot for a .88 v reading on your SMT-6.

Bill

The O2 readings I posted are the readings I see from my Zeitronics using a wide band O2 and not a narrow band O2.

Perhaps I confused the issue. I deffinately do not want to cause anyone engine damage. Thanks for your comments Jeremy.

Jeremy Himsel

That makes perfect sense.

Tom M'Guinn

On a stock narrow band sensor, .88v represents 12.8:1 I believe, which is a bit lean for "open loop" WOT, and is a bit rich for "closed loop" driving. At any rate, the problem with narrow band sensors is that they (and the circuits used to measure them) are just not accurate enough in real life when the mixture is not close to 14.7:1. For example, .88v (12.8) is probably too lean for WOT, yet .91v is probably too rich. That's a difference of .03v -- any number of things can affect the signal by .03v, such as a dirty connector, older sensor, state of charge, harness aging, ground quality, etc., etc. Wideband units operate from 0 to 5v and provide much better accuracy across a broader range of a/f ratios. If you are planning to tune based on an O2 sensor, it really should be a wideband. Otherwise, I'd use a dyno. I can log both by stock narrow band and my wideband, and based on that would never try to tune my car with the narrow band.

Tom M'Guinn

Just to further clarify, if these are wideband readings, then they are not being used by the engine management system (DME) on the typical 951. The DME uses the stock narrow band sensor which works just the opposite, producing a voltage from 0 volts (very lean) to 1 volt (very rich).

Bri Bro

The voltage will be bounching back and forth between 0.6 and 0.2 volts in closed loop. The engine controller (DME) is making the mixture a little rich then lean centered around 14.7/1 to allow for the proper operation of the cat.

Below is a graph that shows the amount of change in the output voltage of a NB with exhaust gas temperature changes. The changes are large in the rich side of the curve ( 10-14.7) were you want the AFR to be under boost.

fast951

Mike, I included a O2 voltage table in the SMT6 install which you should have. In closed loop, you will notice the AFR hovering between 14 and 15:1 AFR.
Tom, I'm not sure if you are logging the Wideband signal, if so, would you compare the results to the values in the O2 table?

Tom M'Guinn

I have not had the chance to pipe the wideband into the PowerPerfect but will do so in early July. I'll be on a long-needed vacation for a while. I'll send you a log once I get it set up to log both at the same time. Right now, I can log both, but they go to separate files (one SMT6 and one Zeitronix) that are not sync'd up.

fast951

Tom, Enjoy your vacation. Vitesse will be closed starting this weekend till early July with almost no internet/email access.