Adjusting Your Fuel Mixture Via Your 02 Sensor and a Digital Volt Meter

Thought you needed an expensive scanning device such as AutoXray or Diacom to view your O2 sensors voltage readings? Think again! You NEED to do this if you have an adjustable fuel pressure regulator or if you have a Q-jet equipped thirdgen and are changing the metering rods to achieve optimal performance.

You will need:

  • A digital voltage meter,
  • Approximately ten feet of wire preferebly 12 gauge or smaller
  • Wire connectors (Screw type "european" connectors preferebly)
  • Jack
  • Jackstand
  • Wire strippers

  1. Disconnect negative battery cable
  2. Jack up vehicle on drivers side
  3. Locate plastic connector for the O2 sensor near exhaust manifold, Disconnect.
  4. Strip end of materials wire approx. 2 inches to expose core
  5. Put exposed end into one end of the weather pack connector for the O2 sensor and reconnect.. Its a tight fit and you might have to trim or expose some more wire. It also might take a little force for it to snap backtogether.
  6. Route wire away from exhaust manifolds or headers back into passenger compartment. If you plan on using this tuning aid temporarily simply route through door jamb. If not, there is a hole under the power booster in which you can route the wire.
  7. Once inside of engine compartment trim wire to an accessable length. Connect wire to the positive probe of your Digital volt meter MAKING SURE that no part of the wire is exposed in any way so as to not ground the o2 sensor accidentally. European wire connectors worked well for me (the kind with a screw in each end to hold the wire in a plastic connector. Avail. at radio shack)
  8. Use the extra length of wire to make a ground for the Digital volt meter. Under the dash there are plenty of places to ground the wire. Connect it to the negative probe of the digital volt meter.
  9. Lower car, reconnect battery. Start car and turn your Digital volt meter on.

The range is as follows 3mV being the leanest, 1V being the richest. Part throttle does not matter so much as the computer always keeps it somewhere in this range depending several on variables and inputs from other systems sensors. At Wide open throttle the MOST desireable voltage should USUALLY be somewhere between .850mV an .900mV Make adjustments accordingly to reach the desired settings. Remember, the lower the voltage the leaner, the higher the voltage the richer. This also has an effect on spark timing. For instance if your car was running lean prior to adjustment and you had the base timing set to just before knock you may be able to adjust your timing for more advance with more fuel. The same is true vice versa. In addition, if you have an old O2 sensor take this opportunity to replace it as an O2 sensors sensitivity greatly diminishes with increased mileage.

It is imperative that you DO NOT ground the O2 sensor wire. This will KILL your O2 sensor.

Happy Tuning

Pablo Morales This article was for educational purposes only. I do not condone performing this on any vehicle. Attempt at your own risk.