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After seeing this gauge at: http://www.egauges.com/vdo_mult.asp?Type=Air_Fuel&Series=Ultra-Lite I started thinking about what it would take to install an air/fuel ratio gauge in my '79 F-150 {400 with Duraspark ignition). You would have to install an oxygen sensor and I am not sure if it would work without the whole EFI system installed. The advantage being you could really fine tune your carburator by watching the air/fuel ratio in all stages of operation rather than doing timed runs and looking for secondary indications. I think this is a bit too experimental for me to try but the idea interests me. Any thoughts?
At there web site they do say to order the oxygen sensor with the gauge... I assume that nothing else is needed..
i have seen other setups discussed here on the boards and if you just measure the readings from the sensor with a volt/ohm meter you can set your carb etc.. with the readings
I did this on my setup after seeing a web site that explained just what to do.
I have a 73 F250 4x4 w/headers and a Predator carb. I bought some spark plug anti foul threaded caps, cut them and had them welded into the headers. then I bought a single wire O2sensor for about $20 and use a digital multimeter to read it.
it gives a very fast response so you can really tune all the rpm ranges.
Here's some of the notes I saved:
O-2 Sensors and use as a tuning/diagnostic tool
By Paul Ruschman - 2/28/99
The O-2 sensor is used by Automobile manufacturers to monitor the exhaust gases of the internal combustion engine. The O-2 sensor uses two different exotic metals that react, (produce a voltage) in the absence of oxygen. The ECU of modern EFI systems uses this voltage to reference the air fuel mixture. Then the EFI can compensate, in small degrees, to keep the air fuel ratio where the programmers of the EFI ECU want the mixture.
When Fuel and air burn, certain amounts of Oxygen are left, depending on the mixture. The mixture that burns all the fuel is called "Lambda" or "Stoichiometric". "1" Lambda is the complete burning of the fuel or 14.7:1 Air Fuel ratio. (Air fuel ratio is measured by the amount of weight, or mass. I.e. 14.7 lbs. of air for every 1 lb. of fuel.) Anything less than "1" Lambda is a rich mixture and more than "1" Lambda is a lean mixture. I.e. "1.3" Lambda is lean, more air than oxygen.
The O-2 sensor produces a voltage once exhaust gasses heat the tip of the O-2 sensor more than 600 Degrees F. The O-2 sensor will produce form 0- to approx. 1.1 volts. Roughly .48 volts is Stoichiometric, 14.7:1, or Lambda. Maximum Power is achieved with a slightly rich mixture of approx. 12.8:1 or .9 Lambda. Minimum fuel consumption is best achieved with a slightly lean mixture of 15.5:1 or 1.05 Lambda.
This can seen on a quality Digital multi meter such as the Fluke 87 or an Air Fuel Ratio Monitor that is sold by many companies such as K&N, Holley, Edelbrock, TWM Induction, (Jegs and Summit Racing catalogs sell these.) etc… These manufactures sell their air fuel monitors for approx. $120-$170. You can build the same thing for approx. $15-$20 through your local Radio Shack, Norvac, or other Electronics store.
If you use a Digital Multi Meter, you have to use a high quality Digital Multi Meter such as the Fluke 87 due to the high impedance.
The O-2 sensor will respond to changes in air fuel ratio INSTANTANEOUSLY! If you have one cylinder miss fire on just one revolution of the crank, the O-2 sensor will detect it and your Multi Meter or Air Fuel Ratio monitor will show you a spike.
Below is a list of the Voltages referenced to Air Fuel ratio.
If this next section is a little confusing, ignore it for now. Once you become familiar with using the O-2 sensor for tuning and diagnosing driveability problems, then this section will make more sense………..
Don’t think of the O2 sensors indications as rich or lean. Think of them as "all oxygen used up" (around 900mv) and "some oxygen left over after combustion" (around 100mv).
This may seem picky but if you see a low voltage and assume the engine is running lean, you may be looking at incomplete combustion or a miss. More significant yet is a jagged waveform at the high (rich?) side which might look like a cylinder that is lean but could be ‘puff’ of EGR gas (not rich) from a faulty valve. (if you are running an EGR valve.)
Sensors vary but popular pattern is a variation from 0mv to 100mv at the low side to 800mv to 900mv at the high side with an average of 450mv. Oxygen sensors will never stay at the mid point. They will flip-flop from seeing no spare oxygen to seeing some oxygen remaining in exhaust stream. They are incredible devices: so rapid and sensitive that, with a good scope, you can identify vacuum leaks and bad injectors. They are a very underutilized diagnostic tool.
So which 02 sensor is the best? Okay, not the best, but the cheapest? And with threads that will work on something weldable thats cheap? I'd go to NAPA and pick it up tonite, but I'm not too sure what to ask for.
I got a Bosch 11027 for about $25 and then bought some Help anti-foul spark plug covers for about $8. These are found in the area where you get replacement window cranks, snaps, handles, etc... They are designed to go around the spark plug and keep it from getting dirty.
I had the anti-foul's cut so that all that was left was a bung that fit perfectly to the O2 sensor. This was done after trying a hardware store to find a nut and found none.
Then I had them welded into the end of the headers, I use 1 sensor that I just swap from side to side when needed and use a spark plug to close the hole when not needed. (I tell people the extra spark plugs are part of the 'after burner' )
You'll be surprised at how quickly these respond, just rev the engine and it changes instantly.
So the oxygen sensor actually generates electricity? So it has a pos and neg output, and thats it? Or do I need to put power into it. IF so, how much? Thanks
>So the oxygen sensor actually generates electricity? So it
>has a pos and neg output, and thats it? Or do I need to put
>power into it. IF so, how much? Thanks
It does, but you only need one wire. Run the ground to ANY good ground and the pos to the one wire from the sensor. The sensor should be grounded by it's contact with the header or exhaust pipe, also it should be close to the engine, I put mine near the end for the headers.
There isn't a whole lot of information directly available on this, although David Vizard has a book on tuning carburetors. This is excellent, and he explains what you're shooting for in specific carburetor circuits. It's available online in excerpted form, several chapters worth so you can check it out before you buy.
The main thing that helped me was the confidence the wideband gave me that I knew what was going on while tuning (instead of guessing) and wouldn't burn up my engine. Still need to inspect spark plugs carefully. Modern gasoline does not color anything like the days of yore.
What you'll find is if the ignition system for any reason isn't working correctly, a weak spark, or the timing curve is wrong, then it will act like it's running too lean. It takes a good hot spark to ignite a correctly atomized air fuel mixture.
On the other hand a high output ignition with a performance ignition curve will want a slightly colder spark plug or can get into pre-detonation. Excessive carbon in the cylinder can do this too.
Keep in mind when you optimize or calibrate the ignition and air fuel ratio for best performance and economy, certain pollutants will increase, and it will not pass a smog test if required in your jurisdiction.
It sounds strange but a properly running engine in some cases actually has to be de-tuned. If you look at the chart here it shows why. Look how NOX levels spike compared with CO and HC.
Going by what I mentioned earlier, the idea generally is to make sure the power valve or power circuit is correct for your engine (vacuum level and altitude) and not providing additional fuel when cruising on flat ground.
The steady cruise AFR is what you're interested when jetting but, you want accurate numbers, without being skewed by the power or acceleration circuit opening up prematurely when it shouldn't be. Here (at cruise) you can tune for a very economical lean AFR without burning anything up.
If you've tuned the engine well 16 to 16.5 should be no problem at cruise in a carbureted engine. The vacuum advance must be operating to factory spec in order to achieve the factory AFRs. This is ordinarily around 50° to 55° of timing advance out on the highway. Again don't use "hot" spark plugs, start with stock plugs or a step colder in heat range.
On the other hand, whenever the engine is under load, under acceleration, whenever you hit the gas pedal the AFR must never be too lean. Tune one carb circuit at a time, in isolation, jetting first, then fatten up the wide open throttle to a safe level if required.
One thing again about ignition. It helps to visualize what an O2 sensor does. It senses O2 right? Sounds simple, right? Well keep in mind, if the ignition is defective, if there is any misfiring going on the wideband will indicate a lean condition, even though the AFR is pig rich. The reason is because the O2 sensor is looking at the O2 level. If there is an intermittent ignition misfire, the fuel isn't being burned, and neither is the oxygen, so it will indicate a false lean condition. So keep that in mind and make sure the ignition syatem is squared away before hooking up the wideband looking at the AFR.
There isn't a whole lot of information directly available on this, although David Vizard has a book on tuning carburetors. This is excellent, and he explains what you're shooting for in specific carburetor circuits. It's available online in excerpted form, several chapters worth so you can check it out before you buy.
The main thing that helped me was the confidence the wideband gave me that I knew what was going on while tuning (instead of guessing) and wouldn't burn up my engine. Still need to inspect spark plugs carefully. Modern gasoline does not color anything like the days of yore.
What you'll find is if the ignition system for any reason isn't working correctly, a weak spark, or the timing curve is wrong, then it will act like it's running too lean. It takes a good hot spark to ignite a correctly atomized air fuel mixture.
On the other hand a high output ignition with a performance ignition curve will want a slightly colder spark plug or can get into pre-detonation. Excessive carbon in the cylinder can do this too.
Keep in mind when you optimize or calibrate the ignition and air fuel ratio for best performance and economy, certain pollutants will increase, and it will not pass a smog test if required in your jurisdiction.
It sounds strange but a properly running engine in some cases actually has to be de-tuned. If you look at the chart here it shows why. Look how NOX levels spike compared with CO and HC.
Going by what I mentioned earlier, the idea generally is to make sure the power valve or power circuit is correct for your engine (vacuum level and altitude) and not providing additional fuel when cruising on flat ground.
The steady cruise AFR is what you're interested when jetting but, you want accurate numbers, without being skewed by the power or acceleration circuit opening up prematurely when it shouldn't be. Here (at cruise) you can tune for a very economical lean AFR without burning anything up.
If you've tuned the engine well 16 to 16.5 should be no problem at cruise in a carbureted engine. The vacuum advance must be operating to factory spec in order to achieve the factory AFRs. This is ordinarily around 50° to 55° of timing advance out on the highway. Again don't use "hot" spark plugs, start with stock plugs or a step colder in heat range.
On the other hand, whenever the engine is under load, under acceleration, whenever you hit the gas pedal the AFR must never be too lean. Tune one carb circuit at a time, in isolation, jetting first, then fatten up the wide open throttle to a safe level if required.
One thing again about ignition. It helps to visualize what an O2 sensor does. It senses O2 right? Sounds simple, right? Well keep in mind, if the ignition is defective, if there is any misfiring going on the wideband will indicate a lean condition, even though the AFR is pig rich. The reason is because the O2 sensor is looking at the O2 level. If there is an intermittent ignition misfire, the fuel isn't being burned, and neither is the oxygen, so it will indicate a false lean condition. So keep that in mind and make sure the ignition syatem is squared away before hooking up the wideband looking at the AFR.
glad to hear from you. I was thinking somewhat along the same line . . we could depend on the manufacturers to tell us what the sensor readings should be but at the same time we would not know exactly if the sensor is working fine, only to trust that it is working optimally in relation to other variables and the chart that shows typical readings at various environments (KOEO, hot idle, running etc).
What we really need are charts like the ones you showed and/or formulas on how the manufacturers actually tune the car to make sure that the car is behaving like it would in stock condition.
You provided a good idea, which is to really investigate the design and working of a car. . and that's one way of approaching understanding most if not all machines (hopefully): is to not only analyze charts but to understand the physics behind how heat is distributed, absorbed or sensed based on the material used in the engine, coolant and sensors. But of course I don't expect it to be an easy task but i'll look up for resources..
A 2nd idea I had is if I could find an open-sourced simulation software which contains the formulas various manufacturers use to model stock performance like AFR, I believe we could chart them out to get a clearer picture/analysis of what's happening in the vehicle..afterall for the PCM to interpret the voltage, it must have some formula stored in CAN to figure out how hot the coolant is based on the resistivity of the sensor and then turn the fan on etc right?
regardless both ways aren't easy.. and I guess I plan to split my time and attack both avenues. . any other recommendations or suggestions or improvements to my ideas would be great!
Start scouring some the EFI tuner forums archives. They are really thorough. No carbureted engine can approach the AFRs they achieve but the principles are exactly the same.
02-18-2002, 11:49 PM
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