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By Mike Kojima

Editor's Note: Since publishing this article, FordMuscle has recevied a number of questions and comments regarding the test methodology and also how the scores (on page 2) were derived. We have published those comments at the end of this article for your consideration. In addition, note that the the subjective ratings are based on the opinion and experience of the author. Mike Kojima is an engineer by trade, with considerable experience in the import-tuner segment. Mike organized the Wideband Shootout article with help from Westec Performance, Innovate Motorpsorts and EFI University. The opinions within are Mike's, however FordMuscle acknowledges that objectivity could always be improved, particularly through a test in which all manufacturers are present, or invited. We are working on a new comparison in conjunction with many of the manufacturers represented in this article. Stay tuned...

The art of tuning an engine is not new, dating back to the birth of the internal combustion engine over 100 years ago. For a generation or two, methods such as vacuum gauges, CO meters, and the black art of reading spark plugs were the main tools in a tuners arsenal. Due to the lack of accuracy of these methods, tuning was nothing more than subjective analysis and best left to the seasoned professional.

Later, as emissions standards tightened and as racing engines started to produce higher and higher outputs, the need to accurately determine air-fuel ratio became increasingly important. Technology improved and wide band air fuel ratio meters with embedded data logging equipment emerged. For many years this technology was out of reach for all but the most well heeled DIY tuner. The cost of accurate reference level wideband air fuel ratio meters was in the several thousand dollar range.

The affordable meters on the market, at the time, used conventional narrow band O2 sensors- the same type of sensors found in most early EFI cars. Such sensors are only accurate around the stoichiometric range, which is an air fuel ratio of 14.7:1. Accuracy in this range is useless for performance tuning where wide-open throttle ratios may drop as low as 11:1, and certainly in the 13:1 range for most naturally-aspirated engines.

The big breakthrough for the performance aftermarket occurred when Bosch made the LSU4 wide band O2 sensor available for a reasonable price, and the aftermarket responded by making affordable wide band air fuel ratio meters using this sensor. This is a boon to the DIY tuner as now there are many wideband air fuel ratio meters available on the market for a reasonable price.

Not All are Equal
Many questions have arisen since the widespread availability of wideband air-fuel meters.

First, since all of these meters use the same Bosch sensor, and since this sensor is factory calibrated, are they all more or less equal? The answer is no. There is significant difference between the controllers and circuitry used in the various meters. How the sensor's heater is controlled and how the pump current is switched and controlled, for instance, are critical for accurate sensor operation. Other questions also can be posed: Which meter is the best performing one? Which meters have the features I need?

With these question and few subjective answers to be found, we set out to determine which meters were the best. The task was a difficult one but we were determined to find the answers.

The plan was to take eight popular units and test them right out of the box using calibrated compressed gas. We'd then run them for an hour on a test engine, with leaded race fuel, to simulate wear on the sensor. Finally we'd test them again with calibrated lab gas. The compressed gas is from Scott Specialty Gasses and formulated to SAE standards for .8 lambda and .895 lambda (11.76 AFR and 13.15 AFR respectively). The gas gives us a control with which we can test each sensor without introducing variability - such as a change in rpm if we were to use the test engine's exhaust gas. To further control the study we used Westech's expensive ECM LambdaPro which read dead-on for both of the gas controls.

Sensors were tested using laboratory gas specifically formulated to yield 11.76 AFR and 13.15 AFR. This way each sensor sees the exact same "exhaust gas", letting us measure the accuracy and responsiveness of each meter.

After testing with lab gas the sensors were run-in for an hour with race fuel, on a test engine (Westech just happened to have a Chevy motor in the dyno room that day.) The run in simulates the wear and tear a sensor goes through with live fuel and heat conditions.

Nine bungs were welded into the exhaust; eight for the sensors under test and one for Westech's own meter. Datalogging was performed during the engine run-in to assess the capabilities of each meter.

A common power and ground supplied each meter to ensure no other variables influenced the testing.

During the dyno testing, we also logged data from all of the units. This gave us a chance to configure each unit's analog outputs, and to compare response time (latency) and accuracy under various loads, sweeps, and conditions. We also verified that the logged data matched the values displayed on the various gauges and displays. All the units shared a common and robust power and ground setup.

The chart on the following page summarizes our findings across four categories. Of particular note was the issue of re-calibration. All of the units certainly rely on the factory calibration of the sensor from Bosch. The manufacturers may even perform some sort of a calibration of the sensor to their units during their assembly process. However, as far as we could tell, only two units appeared to be capable of re-calibration to compensate for sensor wear. The Innovate unit is self calibrating, while the NGK requires the user to turn a knob until the display reads "CAL." Both measure the air-fuel ratio of free air to calibrate the sensor.

This raised the obvious question: If a unit is not capable of calibration, how does the user know when the sensor is going bad? We know from the Bosch data that the sensors themselves change as they age. Continue

(Air-Fuel Meter Shootout continued.)
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In This Article:
Air-fuel meters are fast becoming an ubiquitous item amongst serious enthusiasts. However, with so many meters on the market how does one begin to select the best one for their needs? We've compared the most popular ones in this article.

Also see:
Double Vision: FAST AirFuel Meter
Taking the Guesswork out of Carburetor Tuning
Super Tuning

From A to Z, we gathered the most popular digital wideband air-fuel meters for comparison. The brands are AEM, Dynojet, FAST, FJO, Innovate, NGK, PLX, Zeitronix.

Part of our analysis was to assess the ease (or difficulty) in getting each unit installed and operating. Wiring up eight units took some time, but fortunately on an engine dyno we didn't need to concern ourselves with a clean installation.


What is a Wideband sensor?
Standard "narrow band" O2 sensors operate between 0 and 1 volts, and are only capable of accurately measuring a stoichiometric air/fuel ratio (e.g. 14.7:1). A richer or leaner condition results in an abrupt voltage change (see Fig 1.) and thus is only useful for qualitative determination. Modern automobiles use this "switch" like sensing at idle and part throttle to make small compensations in fuel delivery to keep the air/fuel ratio near 14.7:1.
Wide band oxygen sensors utilize a more sophisticated sensing element which enable it to produce precise voltage output in proportion to the oxygen in the exhaust (see Fig 2.) As a result a wide band sensor can measure accurately from as rich as 9.0:1 to as lean as free air. Wide band sensors used to be cost prohibitive, however recently their wide spread use has resulted in lower prices.


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