I just made a WOT pass and logged my O2 sensors and knock retard. At WOT my O2 sensor values stayed at about 930 mv, approximately what A/F ratio am I looking at with these values? Is it too rich?

I also got 6.6 degrees of KR at some point, but I forgot to log the rpm's also.

 

The stock PCM programming targets an A/F ratio generally in the area of 11.7:1. That roughly corresponds to 930mV. But the key word here is "roughly". The stock O2 sensors are "narrow band"... they are only intended to function, and to be accurate at 14.7:1 used for idle and low load/part throttle operation. You can not use them for WOT tuning. A smalll change in operating temperature of the sensor can cause a larger mV change than a large change in A/F ratio.

As a rough guide.... your 930mV seems to be very typical for the stock PCM tuning, and you might see more power/torque with a leaner A/F ratio.... say in the 12.8-13.2:1 range. But you need a wide-band sensor to accurately measure those types of A/F ratio.

 

What Fred said, just one thing to add. The hp gain going from stock programming to ~13:1 (where a stock motor will make the most hp) is small. On the order of 5-10rwhp at most. And you have to keep in mind that while being a point rich cost a couple of hp, being a point lean can cost thousands of $$$.

If you do tune with a WBO2, you also have to consider the tuning conditions v. the conditions you are likely to encounter while driving. If you tune on a hot humid day with low barometric pressure, the car can be much leaner on a cool, dry day with a high barometer. A factory tune is probably a bit too lean, but be careful when going leaner as it's that way for a reason.

Rich Krause

 

Thanks for the responses. I knew this method wasn't very accurate to get an A/F reading, I just wanted to throw out my numbers. The next time I have my car dyno'd I'll try to get a WBO2 readout also. As of now I don't have any plans to program my computer, 5-10 hp isn't worth it to me.

 

I was told that the GENERAL rule is to be .900+ to be safe. By the way, what program are you using?

 

I'm using this software:

http://www.obd-2.com