Air-Fuel Meter Shootout (continued)
As previously discussed, air/fuel data is most useful when
correlated with other key parameters like throttle position,
manifold absolute pressure, and RPM. And this sort of correlation
absolutely requires data logging. So, even though all of these
units feature useful real-time displays, the most important
parameters are response time and the quality of the logging
solution. Response time is critical because it's possible
to have accurate data, but, due to high latency/delay, the
data is essentially in the wrong
column of your fuel map.
Results - At a Glance
Listed below, from A to Z, are the eight meters we tested.
All use the Bosch LSU4 wideband oxygen sensor. There was a
surprising amount of variation between the various units,
in terms of both accuracy and response time. We also rated
the ease of use, display, and included software. The participants
were AEM, Dynojet, FAST, FJO, Innovate, NGK, PLX, and Zeitronix.
The AEM unit was accurate during our tests, but with no
real data logging capability, of limited usefulness for
actual tuning. It was average for response time.
The NGK unit exhibited low scores for accuracy, and it
was missing the required wire for analog output. It does
not have data logging capabilities. Considering NGK makes
their own wideband sensors, it is a surprise this unit
ships with a Bosch sensor.
The Dynojet unit was hard to set up, and the included
logging software was very limited. The Dynojet exhibited
the slowest response time tested.
The FAST unit had internal datalogging, but no separate
logging analysis software. This perhaps makes it less
useful for complex tuning, but is really "to the
point" for those wanting no-frills wideband tuning.
Setting up the analog outputs was somewhat difficult.
Display is nice and intuitive. More
on the FAST unit.
The FJO unit had tricky wiring for the sensor, the controller,
and the analog outputs. It was also difficult to setup
the analog outputs with the included configuration software.
The included logging software was counterintuitive.
The Innovate unit was accurate, exhibited the fastest
response time, and included very good analysis software.
Innovate claims to be the only truly digital unit, and
the high accuracy and low latency seem to support their
claims. Setup and wiring was complex and somewhat confusing.
The PLX M300 does not include logging software, and exhibited
accuracy at +/1 AFR (the worst tested). Note that PLX
has commented below, and believes we did not wire their
unit properly in that we used a common ground for all
The Zeitronix exhibited accuracy of +/- .54 AFR, and gradual
lean drift under some conditions. The included logging
software was relatively difficult and lacked features.
Note that Zeitronix indicated we may have reviewed an
outdated unit (see comments below.)
The only regret we have is that we couldn't effectively simulate
long-term sensor "aging." Aging is mostly due to
oxidation of the sensors internals and fouling of its ceramic
elements. Operating conditions and fuel type are big factors
in the aging process. Exposure to lead in race gas, metallic
elements in octane booster additives, oil or carbon fouling
and really high operating temperatures contribute to rapid
aging, and a resulting loss of sensor accurancy. Because of
aging it is important to have an air fuel ratio meter that
can be calibrated. The common type of calibration is called
a free air calibration. This is when the meter compares the
output of the sensor to what it should be when exposed to
a know oxygen content gas, air. If an air fuel ratio meter
is lacking the ability to calibrate, the sensor should be
replace at regular intervals. The trouble is when should the
sensor be replaced? It takes some experience to know when
this is appropriate.
We did try to emulate this idea using a variety of old and
damaged sensors we had laying around. With one of these sensors,
the Innovate XD-16 would show an error code indicating that
the sensor was bad. However, when we connected the same damaged
sensor to any of the analog gauges they read as much as 3
AFR off. Again, the obvious question is: If your gauge can't
tell you when a sensor is bad, how could you ever trust it?
Optimizing Wideband Sensor Usage
Other things to keep in mind to ensure proper sensor function
and longevity are exhaust back pressure, rich mixtures, and
high exhaust backpressure forces more exhaust into the sensors
pump cell which can cause an air fuel ratio meter to read
richer than what the engines really running. Turbo engines
run a relatively high amount of backpressure in the exhaust
manifold before the turbine, making them a poor place to locate
Missfires due to a malfunctioning or underpowered ignition
or an extremely rich mixture can cause false lean readings
because unburned liquid fuel in droplets block the small hole
leading to the sensors pump cell.
A wideband sensor should not be placed in the exhaust stream
and left unheated. The hole to the pump cell can quickly become
clogged and contaminated by exhaust byproducts, especially
during a start cycle from a cold engine. The sensor can also
be damaged by exposing it to temperatures above 700 degrees
C, like those typically before the turbine in turbo engines.
You never want to place a sensor there anyway due to the aforementioned
issues with sensor accuracy and backpressure. Lastly you don't
want to place the sensor so far away from the engine that
its 10 watt internal heater cannot keep the sensor hot enough.