From what I've seen, these gauges are worthless. Your ECU will constrantly be compensating so you will see it swinging back and forth all of the time. Don't worry about it. The reason why is in the archives and you can find it on vfaq.

Thanks a lot buddy. Thats a big help. It was constantly changing, so I was thinking something was wrong. But thanks again!

btw: This is all courtesy of Todd Day (bow your heads in respect to his work)

essentially, your car will be running rich, the exhaust will pass the O2 sensor, it will register this, lean itself out, over compensate, O2 sensor will register this, richen the mixture, over compensate, etc... so that's why you keep seeing the values constantly changing.


What is an air/fuel ratio gauge?
What is an A/F gauge?

An air/fuel ratio (or A/F) gauge is a voltmeter attached to the oxygen sensor signal wire. The oxygen sensor reacts to the amount of air present in the exhaust stream, and provides an approximate indication of the relative amounts of air and fuel in the combustion mixture. It is a useful tuning tool, although limited somewhat by the characteristics of the oxygen sensor it is attached to.

There are many A/F gauges on the market. Those for DSMs usually read from 0-1V, although newer models may measure a restricted range similar to 700-1000 mV.

Because the A/F gauge is merely a voltmeter, many people have adapted existing equipment or built their own, rather than pay retail prices. One such design is provided free of charge by Brad Bauer, and is based (as most are) on the National Semiconductor LM3914 bargraph display driver IC.

Some DSMers have also offered their homebuilt units to other club members at lower prices. These offers are usually temporary.



What is an A/F meter?
Has anybody ever installed an A/F meter on a [DSM]?
How do I install an A/F meter on a [DSM]?
I can't find the O2 sensor wire! Where is it?
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An A/F meter is simply a voltmeter, hooked up to the oxygen sensor. Most A/F meters are simple bar-graph displays, although some have LCD displays. Since the

Installing an A/F meter is as simple as connecting the meter to power, ground and the oxygen sensor signal. Owners of precise meters will want to be certain to get a good ground, since ground offsets may affect the A/F meter readings.

1Gs have a test connector, located in the passenger side of the dash, that is useful for A/F meter connections. This wire can be located by following the directions on Brad Bauer's O2 sensor wire VFAQ.

2G owners need to connect to the ECU wiring in order to monitor A/F ratios. You can find the correct wire by reading the hawaii.dsm.org 2G A/F install How-To.

The "Blinky Light" air/fuel gauges are a piece of garbage. The only ones that are remotely correct are the ones that read the actual voltage off of the 02 sensor.

Straight off of RRE's website:
95-99 Turbo
On 91 octane gas you will want .94-.95v If you are at a higher altitude then lower voltage is OK.
On 92 octane gas you will want .94v
On 93-94 octane gas you can get away with .92v

When the O2 sensor heats up after several runs, the voltage out put will drop off a little. What was .94v will drop to .92v. This is normal.



90-94 Turbo
The O2 voltage will vary a lot more from car to car. Your numbers can vary from these easily by as much as .05v. 1G cars have more grounding issues and 90s in particular will read leaner (lower voltage) With a 1G car the compression is lower too so you can run leaner before getting knock that retards timing.

On 91 octane gas you will want .89 to .91v If you are at a higher altitude then lower voltage is OK.
On 92 octane gas you will want .88v
On 93-94 octane gas you can get away with .86v

The same applies to the O2 Voltage when the O2 sensor heats up, it will drop some.

The A/F gauge is best connected to the stereo output. DSM O2 sensors are barely more than binary devices (enough/too much) and trying to get information out of them is like calling the IRS for tax help.

I installed an auto meter a/f gauge on my 90 tsi. I used the single wire connector under the right side kick panel and the gauge never moves one point from all the way lean, it stays in the red and doesnt move even when the car runs for a while. i havent hooked it up any othe way. The gauge worked in the car it was taken out of. I am stumped???? please help