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.

AEM 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.	AFX (NGK) 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.
Dynojet The Dynojet unit was hard to set up, and the included logging software was very limited. The Dynojet exhibited the slowest response time tested.	FAST 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.
FJO 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.	Innovate 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.
PLX 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 units.	Zeitronix 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 under/over heating.

A 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 the sensor.

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.