MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Tuning with an O2 sensor

Perhaps I am trying too hard, but I am going to install an oxygen sensor and an air fuel mixture gauge in my 69 B to help in carb tuning and needle selection. Problem is, that the O2 sensor is supposed to be mounted in the collector where gas from all cylinders passes by. That is quite a long way from the engine and I am concerned about the exhaust gases cooling off before reaching the sensor(it operates at about 600 degrees F). At the collector will the gases still be at 600 degrees? Does anybody see a problem with installing the sensor in the cast manifold and measuring the gases from cylinders 2 and 3? Or would this provide an inacurate reading--?
Thanks,
Robert
Robert

The gases will still be above 600F at the junction. Reading just 2&3 is probably OK since that is both carbs. All assumes that both carbs are carefully kept equal in all respects. It would be a lot easier to install the O2 sensor in the steel pipe rather than the cast manifold. Be aware that the common O2 sensor is not really good for the task, as there is very little slope to its response; it is pretty much a device of lean-or-not readings. The multi-light "fuel ratio gauges" are considered by those who know to be a scam, in that the progressive lights seem to tell you more than they actually do. There is a much better but much more expensive wide spread sensor. All that said, I believe that the cheap O2 sensor read by a voltmeter would be a useful tuning aid and I am incorporating O2 fittings in any new exhaust systems I build.
If you want more, email direct and I will look up some references to give you.
FRM
http://www.usachoice.net/gofanu
FR Millmore

Adding to what FRM said I think the sensor might get too hot in the manfold. Exhaust manfolds will sometimes burn heat resistant paint and have been known to glow in the dark if the mixture is out or the timing retarded. It will work ok at the collector but as FR said it will not be accurate away from stoich (14.7). Denis

DENIS

If you use a heated sensor you could place it anywhere in the exhaust you like. The least expensive I've found is Bosch part number 13275. But it still has the problem FRM mentions -- it's more a binary rich/lean indicator, not a progressive mixture indicator....
Rob Edwards

A 3 wire heated 'broadband' 'wideband' sensor is what is needed. They are more expensive than the Bosch. Do a google search
Mike MaGee

BTW, I use a portable a/f meter to check the mixture. Works ok but the mixture balance on both carbs need to be in unison to use.
Mike MaGee

Check out the supercharger bbs for discussion of O2 sensors and their usefulness for tuning a B motor. You may also find information about sourcing the appropriate units.

Dean
Dean Lake

Ok, so the best place to mount this sensor is going to be just after the collector. the sensor I have is of the unheated type, I would like to avoid having to purchase a different sensor.
Thanks to all for your help
Robert
Robert

This thread was discussed between 05/06/2004 and 06/06/2004

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.