Installing an Air/Fuel Ratio Gauge - 95 Golf 2.0 ABA

1st - Why install one.  So I can monitor the O2 sensor. - So what.  A lot of people have no idea how they work, or what they do.  Read up on this site.. - I can watch my car enter and leave open and closed loop status as well as detect when my O2 sensor is starting to act slow, or if the car is running too rich or too lean at WOT.  In short, the O2 sensor is the primary feedback sensor to the ECU when the car is running.  O2 sensors only work at 600 deg F - and most newer units have an internal heater.  A longer O2 warm up time may be a sign of a failing heater. 

Open loop - Car is cold, Car is at idle, car is at WOT.  ECU "ignores" O2 sensor input and runs in a set pattern.  Open loop and also happen at speeds above 90 MPH, or fixed higher RPM and load ranges (4 people in the car.. running on highway. A/C on)..  Open loop = Bad fuel econ - this is my primary reason for having the gauge.

Closed loop - Car is warmed up, and running at part throttle.  ECU reads O2 sensor, adjusts the injector opening cycles, and the O2 shows the change.  The ECU will switch between rich and lean.  This is done to target the needed correct air/fuel ratio of 14.7 parts of air to 1 part of fuel.  It also helps the cat converter store oxygen to convert bad gasses into good ones.

O2 sensors are small voltage generators - Rich = .9 volts - Lean = .1 volts.  The voltage is very weak and should NOT be placed near ignition coils or cables (plug wires).  Be careful where you route the wires back to the gauge.

2nd - This is a "hot" gauge in the sense that a lot of people have them, "cuz they are cool".  I don't.  I know what it does and I know how to read it.  The gauge should swing back and forth about 1 second while driving (closed loop).  At idle it should still swing, however it may fall out of closed loop.  Stuck on the rich or lean side is not good.  Its normal for the gauge to read full  rich when at WOT.


3rd - Turbo and Go fast guys use these to tune cars and make sure that at WOT things like turbos and superchargers.  Its very bad to run a car lean at high RPMs.  This gauge can help pinpoint system faults.  Honestly unless this is used with a "wideband" O2 sensor and gauge its limited, but can still show issues with your system.  My car does not have forced induction, and I use the gauge as a diagnostic tool.

I mounted the gauge next to the radio, using 42nd Draft Designs little plastic deal.  It's not as easy as it looks to install.  You need to hack away at some of the dash behind the heated seat blanks.  And as an added bonus, the steering wheel completely obscures the mounting.   Ok, so that's been said, I have to crane my neck around to see it, or duck to see it.  Kinda sucks.  Don't ask what the switches do.

The gauge is a cheap unit form Pep-Boys, $25.  I refuse to spend $100 for a black AutoMeter unit so it "matches" the other gauges.  It works fine, the center lights up white and the LEDs dim when the dash lights are on.  The gauges needs 4 wires - 12V Ign, Ground (engine block), Dash Lights, and O2 sensor signal.  The o2 Sensor signal and engine ground need to be run into the cabin VIA the rubber grommet near the clutch pedal.  The Dash lighting and 12V+ Ign I took from the headlight switch.  The gauge comes with enough wire to run over to the headlight switch, you'll need extra wire for the sensor signal and engine ground.

(Later, I did install a nice black Autometer unit., it does look a lot better. )

Its very, very important to wire the gauge up right, and use SOLDER and HEAT SHRINK on the connections.  Do neat work.  The gauge is taking the signal from the O2 sensor and this wire also goes to the ECU.  The ECU must "see" good clean connections, and since the voltage is weak, and wire damage, water, or corrosion will change how the ECU works, and throw off the gauge.  This is why the gauge needs to be grounded to the engine block.  I cannot stress this enough.  If you have a ground potential difference of 1 volt between your dash and engine - the gauge will never work..  And this seems to be the biggest issue when installing the gauge.

Note on the above picture where the O2 sensor is located, and where I added the ground for the gauge.

Close-up of ground.  I removed the paint under the allen  bolt, and SOLDERED and CRIMPED the ground wires.  One of the wires goes to a oil pressure gauge block, the other for the A/F gauge.  Note, there are also 3 engine block grounds under the lowerintake on the ABA engine.

This picture is actually wrong my car, but you get the idea.  All and all, you need to tap into the line that runs from the BLACK wire off the O2 sensor, and goes to the ECU.  Again, do this carefully.  In my car, its a green wire.

The wire I used was the green wire, all the way to the right side of the connector.  With the air intake boot off (hey, why not clean the TB) its pretty easy to get down onto the connector, and clip the wire, and solder a tap off of it to the A/F gauge.  I ran the wire up into the plastic wire loom cover below the rain tray, and over the coil, down next to the master cylinder and booster, and into the rubber grommet.  Use a good quality heat resistant wire loom cover to protect the wire, and make sure it will not fall and lay against your exhaust.

Once the gauge is wired up turn on the car, the gauge should light up, check the dash lighting..  Fire the car up, it may take up to 30 seconds for the gauge to start to move... it will start out slow, then start to more faster once the sensor warms up.  If your car is OBD II (96' and later) you'll have two (2) O2 sensors.  You want the sensor IN FRONT of the converter...

If the gauge lights up, but does not move, check all your connections, and try it again..

Good luck!