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MG MGB Technical - Wide band a/f controller

With modern fuels being different from when my car was new and having changed the air cleaners and all sorts of other parts I can't be sure that the SU needles I am using are the best.

Off the shelf wide band systems are quite expensive and sensors must now be available out of scrappers. So to enable me to measure what is going on I am interested in building a DIY wide band controller.

When I searched in google the sites that came up tended to be a bit old. I am not worried about a bit of soldering. It looks to me as if the gauges are quite expensive. So a set up that feeds to my lap top might be good as I will only need it to get the carbs set up and then to check the tune from time to time.

Any help appreciated.

David
David Witham

David most cars that would be in the scrap yard would have narrow band sensors as thats all that is needed to tell the computer mixture info. A Bosch wide band sensor is not expensive and is what most test units use. It must be a self heated unit if you are going to stick it up tail pipe.
Denis4

Hi David,
I have an a/f (O2) gauge setup permanently and indiscreetly mounted in my car. It helps a lot when playing and experimenting with setups on the car. I don’t know how I could have worked without one previously. It is accurate and can measure "half a turn of a flat" in the jet setting on my HS2 carbs.
I used narrow band O2 sensor (with heater (4 wires)) taken from a "plastic" car in a scrap-yard, cheap. All it needs is a 0 to 1 volt voltmeter to read its signal. The O2 sensor is mounted where the manifold becomes a single pipe. It takes about 10 seconds to respond properly from a cold start-up.
As it is difficult to find/get a 0-1v meter, I built a neat cheap one to test the system using 10 LED lights from a sketch I was given. The middle two lights are green, indicating the mixture target.
You do have to build faith in the unit as you can get the lights to go up and down like a yo-yo. You can also get them to stand still with only a small instant fluctuation at a change in throttle opening. The hardest part is to find/make the perfect jet.

Having fun and going in the right direction is the best part.

Regards,
Richard.
RH Davidson

Since posting the question i have found www.14point7.com which looks quite interesting.

Richard, your narrow band with the LEDs sounds quite good. Do you still have the sketch?
David Witham

I knew you would ask. I built it about 2 years ago. I'll to go through my files to find it for you.

Richard.
RH Davidson

http://www.buckeyetriumphs.org/technical/Carbs/AFMonitor/AFMonitor.htm
werner haussmann

Yip, Werner found the updated one.
I initally used - http://www.pelicanparts.com/techarticles/mult_air_fuel_monitor/mult_air_fuel_monitor.htm.
I am now using the M7009 as shown in http://www.airfuelratiometer.com/

Regards,
Richard.

RH Davidson

This is where it started for me. http://www.lambdasensor.com/main/mcolours1.htm

Richard.
RH Davidson

A narrow band A/F meter is, better than nothing and good for testing for mixture at a fast cruise as thats the only time your using stoich (14.7:1) their accurate at that but apart from that will only read "rich " and "lean" above and blow but not how much. The SU carb when set up right needs about 12:5 at idle and power, 14,7 light power cruise and will lean out to 16.5 on a light throttle cruise. You want a rich mixture for idle and power and a leaner mixture for economy at cruise. The SU will do all this with the correct needles and balance. Like I said better than nothing and with the recommended needles, a NB would give you an indication of your mixture for 75% of your driving, But if you want to tune for power and economy the wide band is the way to go. I had mine fitted to the car all the time but fond I was looking at it too much and not where I was going, so now it is only fitted at tune up time. Wide band are getting cheaper all the time. I use a LM no dater logging just a gauge and its great. Denis
Denis4

This thread was discussed between 27/05/2009 and 02/06/2009

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