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The modified Autometer A/F gauge is sold by: ww.gadgetseller.com An existing Autometer A/F gauge can be modified, and re-calibrated for about $25, plus postage, on a one day turn-around. There are some other brands of A/F gauges that can be similarly converted. Basically, the conversion increases the resolution of the gauge by a factor of 5, but only displays the 0.2V range of most interest near WOT. A calibration sheet is provided with the modified gauge. The problem with an ordinary Autometer narrow band A/F gauge is that the full 0-1.0 volt scale is represented by 20 flashing LEDs. It covers the full range from very lean to very rich. Not much sense can be made from the blinking LEDs in the critical area near WOT, where one LED might represent a significantly large A/F ratio change. For tuning and monitoring purposes near WOT, there is not much need for A/F ratios at, or leaner than, stoich (14.7/1), which is about 4/5 of the oxygen sensor's total voltage range. TUNING: The hard part is to assign A/F ratios to what is seen on the gauge. A specific A/F ratio can be estimated by using other inputs. A portable wide band oxygen sensor would be best. But, the A/F ratios from the OEM oxygen sensor on UTEC data logs can be used to establish some data points, as can the OEM ECU in closed loop fuel trim mode. With a few data points, and some subjective interpolation, an estimate can be made relating voltages to A/F ratios to the curve published with the original Autometer gauge instructions. For example, it is possible to assign voltages (specific LEDs) to estimated A/F ratios. My voltage of 0.85V, near the mid (#8) yellow LED equates to an A/F ration of about 13.5/1. The rich area from 0.90 to 0.95V is about 12.5/1 and 10.5/1, respectively. Now, when the UTEC logs show "rich", it is possible to estimate just how rich, with at least some confidence with the modified gauge. MONITORING: Most tuners only use a wide band oxygen sensor just while actually making tuning runs, and not as a full time monitoring gauge. The wide band sensor is very expensive to replace as it ages because of continuous use. This is where the modified Autometer A/F gauge really shines. It is there all the time and has the sensitivity to detect small changes that might not otherwise be noted, much less than those that would trigger a CEL warning. If there are very small changes in the fuel delivery, such as fuel pressure variation, or changes in the air flow downstream of the MAF sensor, it will show up on the higher resolution modified A/F gauge. BOTTM LINE: No, it is not a subsitute for a quality wide band A/F gauge for tuning, although it is possible to make some reasonable tuning adjustments based on what it displays. But, it works really fine as a safety monitoring device, and it is a very cost effective alternative compared to having no useful, real time A/F information.
This in depth summary was written by my good friend Bob Kanan who was the first in North America to alcohol inject his wrx. Each LED represents .1 and range from .79-.99 volts to ensure extremely accurate readings, especially during WOT.
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Linear Mode
