McIntosh

I'm curious if anyone else has tried this or has an opinion on it.

I installed a bung after my header collector and installed a single wire O2 sensor. I ran a wire from it into the cab and attach it to a volt meter. I ground the other volt meter lead and have a makeshift narrow band O2 sensor. My cheep digital multi meter displays volts to the thousandths which seems to work better than my much more expensive "Fluke" meter. Everything I read says these O2 sensors produce from 0 to 1 volt with 0.45 being stoichiometric on gasoline. However, looking at a graph of output voltages/ ratios, anything from 0.5 to 0.9 seems pretty close to me. When I first installed it I was reading a solid 1 volt. I jetted my mains down 2 sizes at a time several times and now see anywhere from 0.750 to 0.980 maybe even bumping into 1 volt occasionally. Idles at a stop light around 0.650. I think I could safely go one or two more sizes down on my mains.
Car runs much better now.

Thoughts?

matt69olds

What your doing is exactly what the OEM did with the first generation of oxygen sensors. You don’t NEED all the fancy gauges and scanners, they are just easier.

shiftbyear

What carburetor are you using? Did you reduce your jet size minus 14?

McIntosh

I purchased a "Brawler 770. It came with #72's main jet size. I've reduced them to #68's. I havent touched the secondarys yet.

shiftbyear

A good main jet test is a long fairly steep grade so you're running off the jet and not dipping into the power valve, you may need a vacuum gauge to ensure you don't go below the power valve opening rate. If the car is surging during the test it usually indicates a lean condition. There are YouTube videos on jetting and Holley's website.