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Old 05-29-2019, 05:46 PM   #1
leon bee
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Default Air/Fuel Meter/gauge

This has been mentioned lately and I'm interested, but completely ignorant about it. When we get past about the mid 80s, cars got a lot of stuff I don't know about.

I googled this, mostly what I found was 2 or 3 hundred dollar gauges to install. I'm guessing there must be a version for shop testing? Looks like you weld a bung in your exhaust, is this always required?

Anyway, I'd just like a little practical information about this with our old cars. Thanks!
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Old 05-29-2019, 06:20 PM   #2
Kurt in NJ
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Default Re: Air/Fuel Meter/gauge

yes, you need a bung in the exhaust---then a "oxygen sensor" gets screwd
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Old 05-29-2019, 08:12 PM   #3
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Default Re: Air/Fuel Meter/gauge

I have a "sniffer" on the short exhaust pipes on the engine on my engine test stand. It is a tube welded to a "C"-clamp that clamps to the exhaust pipe that the sensor screws into. It's a relatively common way to temporarily mount an exhaust sensor to an engine.
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Old 05-29-2019, 08:19 PM   #4
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Default Re: Air/Fuel Meter/gauge

I nave the weld in bung on my 33 .34 and 28 A, an easy way to het the mixture right. we use an inovate setup .
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Old 05-29-2019, 10:18 PM   #5
Ol' Ron
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Default Re: Air/Fuel Meter/gauge

Back in the "Day" we could read the plugs, the new gad deleted that? Yes It's a better way to get thepower and cruise ratios right. I tune all my engines for economy, but you have to make sure the engine doesn't go lean on power. It takes a good ignition system to get both.
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Old 05-30-2019, 04:58 AM   #6
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Default Re: Air/Fuel Meter/gauge

I have a A/F gauge in my coupe. They're very easy to install, but you need a welder or a buddy that will weld in the bung for you. For a blown motor, it's crucial to have the right air/fuel mix
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Old 05-30-2019, 08:04 AM   #7
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Default Re: Air/Fuel Meter/gauge

Do you need two for dual exhaust?...should they be close to the engine... Thanks.... Mark
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Old 05-30-2019, 08:16 AM   #8
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Default Re: Air/Fuel Meter/gauge

There is a specified distance to locate the sensor from the ex valve for the best readings. Not sure how critical it is, but with a turbo (the installations I am most familiar with) they what the bung located in specific locations.
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Old 05-30-2019, 10:10 AM   #9
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Default Re: Air/Fuel Meter/gauge

It's best to follow the manufactures specs. They all ask for something a little different.
Only one is needed.
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Old 05-30-2019, 10:43 AM   #10
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Default Re: Air/Fuel Meter/gauge

Another thing about a "sniffer" is that it can be moved from one pipe to the other if you are running duals. It may not be quite as accurate as a properly placed bung, but you can check both sides with one gauge.
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Old 05-30-2019, 11:16 AM   #11
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Default Re: Air/Fuel Meter/gauge

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.
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Old 05-30-2019, 03:49 PM   #12
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Default Re: Air/Fuel Meter/gauge

When Richar Kunc was doing all his research on the ignition system. He picked me up at the airport in his 53 Ford HT with the 276, L-100 engine. The af meter was right in front of me. On the 60 mile trip back to his house, the meter was in the lo to mid 15's and hi 12's on accelerating. 22 mpg. That's what you can do with the right "Stuff"
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Old 05-30-2019, 08:17 PM   #13
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Default Re: Air/Fuel Meter/gauge

Thanks!!!.....Mark
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Old 05-30-2019, 10:48 PM   #14
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Default Re: Air/Fuel Meter/gauge

I can't say I understand much yet.....but I will. No problem putting bungs into pipes. If I could just get the Hudson Hornet off our lift I could work under my Ford again.
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Old 05-31-2019, 12:12 AM   #15
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Default Re: Air/Fuel Meter/gauge

Quote:
Originally Posted by Ol' Ron View Post
When Richar Kunc was doing all his research on the ignition system. He picked me up at the airport in his 53 Ford HT with the 276, L-100 engine. The af meter was right in front of me. On the 60 mile trip back to his house, the meter was in the lo to mid 15's and hi 12's on accelerating. 22 mpg. That's what you can do with the right "Stuff"
Those are good readings. You will hear people always quote 14.7:1 as being the preferred ratio. That is the exact ratio to make the catalytic converter work correctly and still let the engine run decent. Without a catalytic converter we can do better than that. 12:1 is perfect performance air fuel ratio and 15:1 is perfect for maximum fuel mileage. We had Dodge vehicles with carbs at work that ran 16:1, that was a little too lean. They always felt like they were right on the verge of a lean misfire. Your friends '53 Ford'd flathead is dialed in, you can't get any better than that. The air fuel gauge is such a neat tool. I will never build another car without one.
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Old 05-31-2019, 12:31 AM   #16
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Default Re: Air/Fuel Meter/gauge

Here is a video so you can see one of the these gauges working while selecting the correct main jets. You can read the comments about the video and see how many different opinions there are selecting air fuel ratios.

https://www.youtube.com/watch?v=2DYLhJ4hhx0
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Old 05-31-2019, 01:05 AM   #17
leon bee
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Default Re: Air/Fuel Meter/gauge

Something about those gauges doesn't look like 6 volts to me.

Thanks for the youtube link.
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Old 05-31-2019, 03:43 AM   #18
51 MERC-CT
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Default Re: Air/Fuel Meter/gauge

Quote:
Originally Posted by leon bee View Post
Something about those gauges doesn't look like 6 volts to me.

Thanks for the youtube link.
Seeing that you are limited to a 6 volt system is different story.
The AFR gage is really only needed to set up the carb.
But if you truly want to use a gage then it can be installed and used with a small stand alone 12 volt battery such as the many 'jump-pack' batteries that are available.
Using stand alone battery eliminates any polarity concerns.
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Last edited by 51 MERC-CT; 05-31-2019 at 07:20 AM.
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Old 05-31-2019, 06:12 AM   #19
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Default Re: Air/Fuel Meter/gauge

Also, you might be able to use something like this to boost the 6V to 12V. I use a similar product on my tach drivers and they work quite well/ Polarity is also a concern.

https://www.amazon.com/eBoot-Convert...11-spons&psc=1

Last edited by tubman; 05-31-2019 at 06:38 AM.
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Old 05-31-2019, 06:23 AM   #20
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Default Re: Air/Fuel Meter/gauge

One of the reasons the opinions vary WIDELY on what the A/F should be set to is the variances between different meters. There is also the fact that differing engine systems can dictate the requirement for different mixtures. I have tested several brands of A/F meters under the same conditions and found that the owner should plan to experiment beyond what the meter is indicating.
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