I suppose we've all been there once or twice. Pull up the codes on your vehicle in hopes of finding the source of some rough idling or stalling. Instead, you end up finding that your battery has been disconnected at some point in time and there is a problem with your O2 sensor. So, you run to the parts store and shell out 30 bucks for a sensor and probably still have problems. Fact is, I rarely see a ride that doesn't turn up these codes; but, is O2 replacement really neccessary???
Back in school, I remember my professor of basic electronic devices devoting a full day to the discussion of O2 sensors and how they never go bad. (Actually, he was head of the electrical engineering department.) His claim was that carbon built up on the sensor and impeded its function. The rememdy was to burn off the carbon. This could be done with a propane torch (carefully!) or simply removing your air filter to lean out the mixture, and going for a ride on the highway. I must confess, I haven't replaced an O2 sensor since.

However, I have installed them in places where they didn't come. Without the years of experience sometimes needed to tune a carb, this mod can get you mighty close. Merely aquire an O2 sensor (bone yard?) and the matching threads (spark plug anti-foul adapter). Drill a hole and weld the adapter as close to the engine as possible, but where the pipes come together. Screw in the O2 sensor and hook a cheap voltmeter up. Low volts and your lean, high volts and your rich, in the middle is what you want. Works for me, any comments?

 

Tru the number 1 thing that causes an O2 sensor to go bad is carbon build up, you must remember that an O2 sensor is merely a galvanic battery. There is a element called zirconium that is impregnated into the sensor element. As time goes on carbon builds up on this, but it also gets depleted over time, being burned off and blown out the pipe. This is the same for catalytic converters, but with platnum instead.

When testing an O2 sensor it is important that it is able to reach at least .980 volts, and should dip down to under 1 volt. But just as important is it's reaction time. If the O2 sensor doesent react fast enough, the fuel control will be all screwed up, thus also reducing the efficiency of the catalytic converter. You should see at least 20 cross counts on a ported injection system.

There are many people running in dash A/F ratio meters, most because of forced induction. While running stoich (.450 volts) is the most efficient on a well tuned engine in good shape, this will change as an engine gets older, or if it goes out of tune (timing, leaky valves, etc...) which is where a gas analyser is the best way to tune an engine. Also when an engine is put under more heavy loads it will require more fuel to make the power desired, otherwise known as power enrichment.

Just a few thought that came to mind, sorry for the rambling.

Nick from the frozen north
1974 F-250 4X4
soon to be 429
dana 60 front and rear

 

Ramble on, man. Thats how we learn. Thanks for the comments!

 

We are looking at a dyno for our machine shop.
I have seen that more people are using O2 sensors in place of exhaust
probes.

My brother is a mechanic in Minneapolis and he uses his digital oscilloscope on the O2 sensor. He showed me how you can spread
the pattern out to see a reading for each cylinder.

He also used it on the MAP sensor was able to see each intake pulse.

I thought that was pretty cool.

I person I talked to used to work at Ford in the dyno area and he said they did not use the air flow meter on top of the carbs.
He said they were not accurate for them because the pulses going back and forth through the carb was the same air being measured twice.

They used O2 sensors and calculated the air flow knowing the fuel flow.

 

That is pretty cool. I have an analog oscilloscope and have stuck it on just about everything on my engine. I never thought the O2 sensor was that fast though. I'll have to check that out. Thanks.

 

Hi RanDawg,
I was going through the archives and came upon your post. I agree that using a standard O2 sensor with a voltmeter can give you a reasonably good idea of fuel mixture. Any of the in dash LED A/F meters are just that. They work quite well if you are tuning strictly for power in the 11.0 to 13.0:1 range, more or less. Problem is, the output really isn't linear, and almost useless below 14.7:1. If you're serious about tuning with an A/F meter, you really need a wide band. Prices have dropped significantly for them, and they are easily available. I have both the US DIY and the OZ DIY, but use the OZ because I have the direct read out display.
BTW. I sent you a private message the other day, did you get it?
Regards,
Robert

 

Yes, I received your message and have sent out a reply.

I was wondering though, is there a better way for a novice to tune a carb? Carb tuning seems to be a bit of an art. I agree the voltage to mixture plot looks a bit like a poorly scribbled 'Z', but I was reasoning anything from 250mV to 750mV would be adequate (preferably 450mV). In my truck, I have used the most expensive DVM that Sears sold in 1998. I can get the specs on it if needed, but I assumed it was an overkill for the job nonetheless. I suppose I could be in error. Anyway, the truck runs well, plugs look good, mileage is about what one would expect, and I thought I would pass this tidbit along since someone had brought up the issue of O2 sensors at that time. Since then, as comments indicated, I have learned how fast an O2 sensor can change voltage. And contrary to the beliefs of my professor's, an O2 sensor can wear out, although I have yet to decide how long this takes. Also, I have yet to observe the operation of an O2 sensor with an o-scope, but I will. Some nice comments, Thanks.