chaseincats Posted March 2, 2021 Share #1 Posted March 2, 2021 Hi guys, I just purchased an air/fuel mixture gauge (https://www.amazon.com/gp/product/B00N3VGPYS/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1) and was wondering where to find the number the car should read when driving/idle. Has anyone done this before? The FSM shows fuel percentages but that isn't readable on these gauges it seems. -chase Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/ Share on other sites More sharing options...
TomoHawk Posted March 2, 2021 Share #2 Posted March 2, 2021 (edited) There's no such thing as an air/fuel sensor. How does that gause operate? Edited March 2, 2021 by TomoHawk Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-616949 Share on other sites More sharing options...
chaseincats Posted March 2, 2021 Author Share #3 Posted March 2, 2021 6 minutes ago, TomoHawk said: There's no such thing as an air/fuel sensor. How does that gause operate? It has an oxygen sensor ("o2 sensor") that is welded into your exhaust. All modern cars have this. Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-616951 Share on other sites More sharing options...
heyitsrama Posted March 2, 2021 Share #4 Posted March 2, 2021 Mine sits at about ~10.3 with the choke on to warm up, 12 on idle after warming up, 14.5-14.8 on load ~3k RPM, 14.7-14.9 @ 80-100MPH, cant get it over 100 it pops out of gear 😞 Running SM needles on a 4screw SU. 1 Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-616953 Share on other sites More sharing options...
TomoHawk Posted March 2, 2021 Share #5 Posted March 2, 2021 42 minutes ago, chaseincats said: It has an oxygen sensor ("o2 sensor") that is welded into your exhaust. All modern cars have this. Oxygen sensors measure oxygen. How does the oxygen measure the fuel mixture in the intake manifold? Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-616958 Share on other sites More sharing options...
jonbill Posted March 2, 2021 Share #6 Posted March 2, 2021 1 minute ago, TomoHawk said: Oxygen sensors measure oxygen. How does the oxygen measure the fuel mixture in the intake manifold? The residual oxygen in the exhaust is a reliable indicator of the ratio of fuel and air at the inlet. This is true given a working and reasonable ignition and cam timing. Engine Management systems do work on this basis. I mean, as well as that being an assumption they make, they actually do work well in optimising fuel mixtures. 1 Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-616960 Share on other sites More sharing options...
jonbill Posted March 2, 2021 Share #7 Posted March 2, 2021 In the same way that taking your temperature is a reliable indication of whether you have an infection. Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-616961 Share on other sites More sharing options...
chaseincats Posted March 2, 2021 Author Share #8 Posted March 2, 2021 40 minutes ago, TomoHawk said: Oxygen sensors measure oxygen. How does the oxygen measure the fuel mixture in the intake manifold? It measures oxygen in your headers/exhaust manifold's back piping (not your intake manifold as that's just air not air/fuel). Jonbill also made some good points. Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-616967 Share on other sites More sharing options...
TomoHawk Posted March 5, 2021 Share #9 Posted March 5, 2021 I stand by my original statement that there is npo such thing as a sensor that measures the air-to-fuel ratio, in the intake manifold. Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-617159 Share on other sites More sharing options...
chaseincats Posted March 5, 2021 Author Share #10 Posted March 5, 2021 3 minutes ago, TomoHawk said: I stand by my original statement that there is npo such thing as a sensor that measures the air-to-fuel ratio, in the intake manifold. Again, this is not measured in the intake manifold, there is an o2 sensor welded into the exhaust headers. Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-617160 Share on other sites More sharing options...
TomoHawk Posted March 5, 2021 Share #11 Posted March 5, 2021 (edited) The only place you can accurately measure the air-to-fuel ratio of what goes into the cylinders is to put a sensor into the intake manifold. Even more precisely, is to have a sensor near each intake port. Having an o-2 sensor (whatever "0-2" means) only measures o-2 in that particular spot. Edited March 5, 2021 by TomoHawk Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-617162 Share on other sites More sharing options...
chaseincats Posted March 5, 2021 Author Share #12 Posted March 5, 2021 5 minutes ago, TomoHawk said: The only place you can accurately measure the air-to-fuel ratio of what gnes into the cylinders is to put a sensor into the intake manifold. Even more precisely, is to have a sensor near each intake port. Having an o-2 sensor (whatever "0-2" means) only measures o-2 in that partuicular spot. https://en.wikipedia.org/wiki/Air–fuel_ratio_meter#Wide-band_sensors Link to comment https://www.classiczcars.com/topic/65119-tuning-with-an-airfuel-gauge/#findComment-617163 Share on other sites More sharing options...
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