Forget those people who espouse that an in-car
air-fuel ratio gauge is merely another bling accessory to be hung from the
A-pillar. An air-fuel ratio (AFR) gauge is a must-have for any highly strung
engine – its importance is right up there with an oil pressure gauge or a boost
In this two-part series we’ll look at the specs of
in-car air-fuel ratio gauges currently on the market – all the way from cheap
narrow-band gauges to professional wide-band gauges.
Caused by Incorrect Mixtures
main reason for installing an in-car air-fuel ratio gauge is to be alerted if
the engine is running lean at high load. In these conditions, the chance of
detonation increases, exhaust gas temperature shoots through the roof and you
can expect broken valves, damaged spark plugs, damaged pistons, blown head
gaskets, melted cat converters – all sorts of nasties.
the other hand, an overly rich mixture can also cause damage. In extreme cases,
this can cause accelerated bore wear, spark plugs will get covered in carbon and
you can expect poor fuel consumption.
Excessively lean or rich mixtures can also cause drivability problems.
Entry-Level Narrow-Band AFR Meters
Mixture Display Kit for Fuel Injected Cars
The cheapest air-fuel ratio gauge on the local
market is the Mixture Display Kit for Fuel Injected Cars. This device is
designed by Silicon Chip electronics magazine and retails through Jaycar Electronics (Cat No
Developed in the mid ‘90s, this kit is the most
basic form of air-fuel monitoring – it simply shows a 0 – 1V oxygen sensor
signal across a 10 LED bar graph. Two red LEDs are configured to show an extreme
lean condition while two yellow LEDs at the opposite end of the graph indicate
rich mixtures. Air-fuel ratios around 14.7:1 are shown by six green LEDs.
This kit comes with a printed circuit board, all
necessary electronic components (including 3mm LEDs) as well as instructions.
The unit is extremely easy to assemble, calibrate (using a single potentiometer)
and gives excellent at-a-glance mixture identification. No wonder thousands have
been sold. See Cheaply Monitoring Air/Fuel Ratios
for full details.
Smart Fuel Mixture Display for Fuel Injected
Cars (Silicon Chip/Jaycar)
The Smart Mixture Display is based on the original
version described but brings some useful added features...
First, the unit now incorporates an engine load
input which, when the user-defined load is met, triggers a warning buzzer to let
you know if the engine is running dangerously lean. No need to take your eyes
off the blacktop when you’re really going for it.
Second, the Smart version brings auto-dimming
which is a welcome addition for nighttime driving. The unit also incorporates
improved circuit protection for better reliability. See
Smart Mixture Meter, Part 1
Smart Mixture Meter, Part 2 for how it works and
step-by-step fitment and calibration.
Again, this unit is developed by Silicon
Chip and is available through Jaycar Electronics (Cat No KC5374).
Digital Fuel Mixture Display Kit for Cars
Developed in 2000 by Silicon Chip, this
unit boasts a numerical display of air-fuel ratio in addition to a compact 10
LED bar graph.
The three-digit numerical display is updated every
440ms while the LED bar graph is updated every 220ms. Air-fuel ratios of 11.8 to
20.6:1 are shown and, like the previous products, it’s calibrated by a single
potentiometer. An auto-dimming function is also incorporated.
The kit includes all necessary electrical
components, a case (with a silk screened front panel and laser cut hole for the
display screen) and ambient light sensor (which is visible to the left of the
display). Unfortunately, the unit is not particularly easy to install due to the
bulk of its plastic case.
Sold by Jaycar Electronics (Part No KC5300), this
unit has the bonus feature of a numerical display but it doesn’t have the
all-important high-load lean-out alarm of the Smart Meter. Its bulk also makes
it more suitable as a removable tuning tool rather than a permanent in-car
The Asian-built AutoGauge brand offers several
in-car air-fuel ratio gauges across a very affordable price range.
The AutoGauge Stealth 1 Digital air-fuel ratio
gauge uses a conventional gauge-style body and its 52mm diameter enables it to
be mounted just like your boost or oil pressure gauge. The Stealth 1 Digital
uses a 270-degree circle of LEDs (which are graded green, yellow and red) and
Lean, Stoich and Rich marked segments on the face. It also has a smoked glass
facia (with full ‘blackout mode’ when switched off) and a silver outer rim.
A new Stealth 1 needle-style gauge has also been
released. The Stealth 1 needle type air-fuel gauge has a 270-degree sweep with
an illuminated red pointer, red/blue scaling (marked Lean, Optimal and Rich) and
LED illumination. It also boasts an ‘opening ceremony’ (full gauge sweep with
ignition-on)and, when switched off, the gauge is near-invisible thanks to a
The Stealth 2 is another needle style gauge except
it has a full 360 degree sweep and a 52mm face. The unit features an opening
ceremony, white LED illumination and a red pointer. Again, the glass facia is
smoked and is near-invisible when switched off.
The AutoGauge Stealth 3 is a needle-type gauge
featuring opening ceremony, a scratch-free blackout stealth facia, illuminated
red pointer and the choice of white or red scales. The scale is marked Lean,
Optimal and Rich and the gauge face is upsized to 60mm.
Outside of the Stealth range, you can buy a white
face/silver rim 52mm air-fuel gauge with red, green and orange LEDs providing a
270-degree sweep over a scale marked Lean, Optimal and Rich. But most
eye-catching in the range is the new AutoGauge Ghost Mirror Face AFR gauge (seen
here). This unit has a mirror effect facia which, when turned off, has a mercury
silver mirror finish. When switched on, the air-fuel ratio is displayed on a
270-degree sweep of red, yellow and green LEDs. These different colour zones are
marked Lean, Optimal and Rich respectively.
These gauges can be sourced from most mainstream
go-fast parts specialists and can be found on-line.
Prices: Stealth 1 Digital, Stealth 1 Needle Style,
Stealth 2 and White Face/Silver Rim AFR gauge - AUD$59. Ghost Mirror Face AFR
gauge around AUD$63. Stealth 3 AFR gauge AUD$79.
Stick around for the second and final part of this
series – we’ll look at the more up-market narrow-band AFR gauges and some in-car
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