I have an Auto X-ray scanner and from what I can tell it does not show me the air/fuel ratio. Is there any way of computing the ratio from the data retrieved from the Auto X-ray scanner?

 

The PCM does not measure A/F ratio directly. It will tell you what the "target" A/F ratio is that the PCM is using for its calculations, but not what it is actually achieving. And even the target data is typically only retrieved by some of the softwate scanners or a high-end hardware unit like the Tech-2 that the GM mechanics use.

You can "impute" A/F ratio from the O2 sensor readings, but they are not very accurate at anything other than the 14.7:1 stoichiometric A/F ratio that is used in closed loop. When the PCM goes into power enrichment mode, and targets richer A/F mixtures (typically around 11.7:1 with stock programming), the O2 sensors are operating at a point where very large changes in A/F ratio produce very small changes in O2 mVolt output... and these changes are easilly masked by larger changes that are produced by the sensor's high sensitivity to operating temperature.

 

Thanks for the reply, but I have one more question. How can I find out if my car is running on the rich side and how do you know how to lean the mixture out at WOT to get max HP?

 

You need to use a wide-band AF meter. The most efficient way to do this is on a chassis dyno. But beware of making it leaner without taking into account the conditions. If you dyno on a day with really "bad" air (hot, high humidity, low barometric presure) it will run much leaner on a cool dry day with a high barometer. You need to build in a cushion. That's one reason the factory calibration is a bit on the rich side. I will add or subtract fuel at the track depending on the "density altitude", which takes into account the barometer, temp, and humidity.

Rich Krause

 

Hey thanks!!! That is what I needed to know. I haven't purchased LT1 edit yet, but I plan to in the near future. I was wondering, how much can be gained from leaning out the mixture on an LT1, which only has a few mods (CAI, 160 thermo, Air Foil, no cat, and cat back exhaust)?

Thanks for the help, I am just trying to learn all I can.