Smart Mixture Meter, Part 3

As we’ve covered in the two stories that we’ve already run on the new Smart Mixture Meter (Smart Mixture Meter, Part 1 and Smart Mixture Meter, Part 2), the design uses a lean-out alarm. This warns you if you have your foot down and at the same time, the mixtures are lean. It’s invaluable because it protects you from a catastrophic lean-out condition of the sort caused by a faulty fuel pump or something similar.

The lean-out alarm works by watching both mixtures and the load signal coming from the airflow meter. If the airflow meter signal is high (ie so is load) and the mixtures are too lean for that load, the buzzer will sound. But what if you have a car without an airflow meter? Or a car where the airflow meter works only for low loads? The answer is to use the throttle position sensor instead of the airflow meter.

Doing It

This supercharged six-cylinder Toyota Crown, which uses the 1G-GZE engine, runs airflow metering. However, as we found with the four cylinder 4A-GZE (see The Fueltronics AMFC), the airflow meter is really only used at light loads. When the blower is engaged, the car appears to swap to throttle position as its load input.

The Smart Mixture Meter’s ‘load’ input therefore needs to be connected to the throttle position sensor’s output signal. This wire is easily found by measuring the voltage on each of the throttle position sensor’s connecting wires until one is found which has a voltage output that varies with throttle position.

The load input of the Smart Mixture Meter is then connected to this signal output wire.

As can be seen here, the Smart Mixture Meter was installed in this car with the LEDs remote mounted, rather than soldered directly to the printed circuit board as is provided in the kit. In addition, the two red LEDs showing load and leanness were also mounted so that they were clearly visible (arrow).

This pot on the circuit board adjusts the lean mixture level for the alarm. In this case the LED was set to light only when the mixtures were so lean that they were off the normal LED scale.

The arrowed LED is now on, indicating that a lean condition has been sensed.

The load adjustment was made next. This LED was set to light when the throttle position was above about half.

So when the throttle is more than half open and the mixtures are so lean that they’re off the normal scale, both LEDs light and the internal alarm then sounds.

If required, the sound output of the internal buzzer can be increased by mounting it outside the box or by using a louder design (a current draw of up to 60 milliamps is fine).

Smart Mixture Meter- AutoSpeed Shop [Smart Fuel Mixture Display for Fuel injected Cars - Pre-Assembled and Tested]

The Other Gauges? In addition the Smart Mixture Meter, the Crown boasts some other new instruments and gauges: (1)     Outside air temperature gauge – available now from the AutoSpeed Shop at Thermometer Module with Alarm for AUD$39.50. The probe has been extended (as covered at LCD Temp Display!) and is mounted behind the radiator grille. The button battery has been replaced with an AA-size alkaline that allows the display to be on continuously. (2)     Digital injector duty cycle meter, a kit that will be available later this year for AUD$54.95. It reads out in real time the injector duty cycle – as you can see, at idle in the Crown it’s 3 per cent. The design also incorporates a relay that can be triggered at whatever duty cycle you want, allowing the easy implementation of load-based switching of devices or an over-high injector duty cycle alarm. (3)     Smart Mixture Meter, with the LEDs remote mounted from the printed circuit board. The Smart Mixture meter is available from the AutoSpeed Shop in either built ( AUD$75.96) or kit versions (AUD$27.95) – see Smart Fuel Mixture Display for Fuel injected Cars - Pre-Assembled and Tested and Smart Fuel Mixture Display for Fuel injected Cars . (4)     K-type thermocouple display, a kit that will be available later this year for AUD$69.95. Here it is being used to measure intake temperatures after the supercharger. In addition to its very wide operating range (up to 1200 degrees C, making it also suitable for measuring exhaust gas temps), the design has a relay that can be switched at a specific temperature.