The Ford Barn

Flathead Fever · 03-02-2026, 12:07 AM

Thae cars with stock 02 sensors have them mounted as close to the engine as possible, so they do not cool down at idle. Also, they need to be mounted before the exhaust reaches the catalytic convertor, because it changes the exhausts reading so then it would be no good for checking the A/F reading. We're not concerned with smog, just that the A/F mixture is correct at idle and cruising. The exhaust has to heat the sensor to a certain temperature for it to work. When I was smog tech and I was watching the O2 reading I'd let it idle for a bit and I could see the readings stop producing rich lean readings. The sensor had gotten too cold to produce a signal. Later they came up with electrically heated O2 sensors that will maintain the temperature if the engine idles for too long. I've been retired from being a mechanic now for 16-years and some of this info is getting a little not as fresh as it once was since I don't do it every day like I used to. What I would do is weld an O2 bung into exhaust as close to the engine as possible to keep it hot when it was running. They sell the O2 sensor bungs for this. Then when you're not using it you can remove the sensor and out a plug in it. Just whatever you do, do not coat the treads of the O2 sensor with a lead ant seize, lead with will wipe out a O2 sensor immediately. The fumes coat the pours in the sensor, and it stops producing a voltage. That's the main reason they did away with leaded fuel. I tried it once on an old engine for fun and sure enough and the sensor "immediately" stopped producing a voltage.

One other thing we were required to have by the State of CA for smog testing was a propane bottle with an adjustable nozzle. They wanted the mixtures adjusted so that they were 50 rpm below the ideal ratio, on the lean side. Some engines would barely idle set like that. We do not want our flatheads adjusted that lean, if anything we want them adjusted slightly rich, we don't need to smog them. Still the propane bottle is an excellent way of tuning the idle mixture. If they are too lean and you run the propane bottle over the carbs the idle will go up, if it's too rich the idle will go down, if it's just right the idle won't change. You don't need all this stuff to adjust your engine; people did it long before these tools came along but it's still kind of fun to test your A/F with them. The propane bottle is also an excellent for searching for vacuum leaks. The problem is getting all these tools for one project and then having them set in your garage for another 20-years until you need them again.

03-02-2026, 12:07 AM	#22
Flathead Fever Senior Member Join Date: May 2010 Location: Yucaipa, CA Posts: 1,492	Re: 2x2 on 8BA flathead Thae cars with stock 02 sensors have them mounted as close to the engine as possible, so they do not cool down at idle. Also, they need to be mounted before the exhaust reaches the catalytic convertor, because it changes the exhausts reading so then it would be no good for checking the A/F reading. We're not concerned with smog, just that the A/F mixture is correct at idle and cruising. The exhaust has to heat the sensor to a certain temperature for it to work. When I was smog tech and I was watching the O2 reading I'd let it idle for a bit and I could see the readings stop producing rich lean readings. The sensor had gotten too cold to produce a signal. Later they came up with electrically heated O2 sensors that will maintain the temperature if the engine idles for too long. I've been retired from being a mechanic now for 16-years and some of this info is getting a little not as fresh as it once was since I don't do it every day like I used to. What I would do is weld an O2 bung into exhaust as close to the engine as possible to keep it hot when it was running. They sell the O2 sensor bungs for this. Then when you're not using it you can remove the sensor and out a plug in it. Just whatever you do, do not coat the treads of the O2 sensor with a lead ant seize, lead with will wipe out a O2 sensor immediately. The fumes coat the pours in the sensor, and it stops producing a voltage. That's the main reason they did away with leaded fuel. I tried it once on an old engine for fun and sure enough and the sensor "immediately" stopped producing a voltage. One other thing we were required to have by the State of CA for smog testing was a propane bottle with an adjustable nozzle. They wanted the mixtures adjusted so that they were 50 rpm below the ideal ratio, on the lean side. Some engines would barely idle set like that. We do not want our flatheads adjusted that lean, if anything we want them adjusted slightly rich, we don't need to smog them. Still the propane bottle is an excellent way of tuning the idle mixture. If they are too lean and you run the propane bottle over the carbs the idle will go up, if it's too rich the idle will go down, if it's just right the idle won't change. You don't need all this stuff to adjust your engine; people did it long before these tools came along but it's still kind of fun to test your A/F with them. The propane bottle is also an excellent for searching for vacuum leaks. The problem is getting all these tools for one project and then having them set in your garage for another 20-years until you need them again.