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
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
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
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