The Autometer gauge below which I originally had fitted was connected to the narrowband lamda probe that fed the ECU. All the narrowband lamda probe needs to tell the ECU is if the mixture is rich or lean. When this signal is fed to a display the result is less than ideal. Most of the time the lights simply bounce around from one extreme to the other as the ECU adjusts the fueling. Therefore I fitted this AEM gauge. This uses a new lamda probe which is a wideband and accurately displays the Air/Fuel ratio. The downpipe had to have a new lamda boss fitted just behind the engine and the wires fed into the passenger compartment.
The Gauge allows you to monitor Air/Fuel ratios in real time without the use of a laptop. This gauge includes a 0-5 Volt analog output to interface with most data-loggers or aftermarket engine management systems, and includes an RS 232 serial data output port for data logging without an engine management system. The gauge is calibrated to work with AEM UEGO sensor controllers ONLY. These units display to 0.1 AFR, feature 24 color-coded LED display lights for immediate reference to engine AFR, and have an integrated three-digit real-time display for AFR.
The kit comes complete with both a black and silver bezel and a black and white face which can be interchanged to match the other dashboard instruments.
The guage is a standard 52mm so I could mount it in the same location as where the Autometer gauge fitted.
There are various models in the Autometer range. I purchased this particular model as it has a plain black background which matches the other dials in the car perfectly. Around the outside of the gauge are 20 leds. 4 red ones for lean mixture (0.05 to 0.249V), 10 yellow ones for stoichiometric mixture (0.250 to 0.749V) and 6 green ones for rich mixture (0.750 to 1.0V). I was originally going to mount the gauge in an extra pod in the A pillar but realized this would be too much in your face when driving so instead I cut a hole in the dashboard just below the main dials and behind the steering wheel. I used a regular hole cutter attachment to a drill to cut the hole in the plastic dash. The gauge is 52mm and the closest hole cutter I could find was 51mm which was okay. If you take this approach then be sure to position the gauge high enough up that you can see it clearly though the steering wheel and that there are no wires behind the dashboard where you are drilling. It won't be the easiest of places to get to should you need to solder wires back together.
The gauge comes with three wires, black for earth, red for switched live and purple for the lamda probe input. The lamda probe wires from the probe to the ECU are sheilded and I didn't want to break the shielding to connect up the lead. Instead I dismantled the ECU and soldered the lead directly onto pin 10 on the circuit board which is where the lamda probe input ends up.
In operation at engine idle and part throttle the leds on the gauge bounce between lean and rich which is perfectly normal as the ECU is constantly adjusting the mixture. On wide open throttle (WOT) the green leds light up indicating that the mixture is rich which is the desired safe reading.
Although the gauge is not as acurate as the wide range Lamda probes used by the rolling roads it does give you a rough guide as to whether the engine is running rich or lean at WOT.