[Flathead Fever]

Its the only way to see what your air fuel ratio is under any driving condition. Even if you do not plan to buy a A/F meter now if your building your exhaust system weld a bung in so you will have it for later.

These on not the old fashioned "oxygen sensors" which generated a .1 to 1.0 voltage. The computer used the voltage reading to switch the exhaust from rich to lean (extremely fast) so the catalytic converter could work properly. The A/F ratio needs to be switching above and below to .5V reading from the oxygen sensor. This gives a 14.7:1 A/F ratio for a three-way catalytic converter to work. These new air fuel ratio sensors are sensing the actual A/F ratio. This is an incredible tool for tuning an engine.

New cars can use up to four of these sensors. One on each bank of a V8 engine as close to engine as possible and one after each of the catalytic converters. This is how the computer knows the catalytic converter is still working. If the oxygen readings are the same before and after the catalytic converter it is no longer working.

You do not need two sensors, just one for dialing in your air fuel mixture. Two are used for the computer to test the catalytic converter and to compare one side of the engine to the other (bank 1 and bank 2). You only need two if you are diagnosing a problem such as an engine misfire, vacuum leak, injector problem or mechanical issue. The computer also uses the the separate sensors to adjust the A/F ratio (injector on time) for each side on the engine but that can only be done with port fuel injection. You just need one sensor for what we do. You could install a bung on each side so if you do have an engine problem you can swap the sensor between the two sides. All that will do is tell you which bank the problem is on. You can do the same thing by pulling individual plug wires and watching the rpm drop.

We had the sniffer on the smog machine along with the dyno but you cannot simulate a real world load on the vehicle unless your driving it.

Install a A/F gauge and a vacuum gauge in you car and you will learn a lot from watching the readings.

When you get the timing and A/F ratio dialed in there is still a little known trick for adding one more horsepower to your Flathead. You don't even need a dyno to detect it.