Having read posts on this board about setting fuel air mixture using the oxygen sender readings it occured to me that it might be possible to make up a similar system as a separate instrument.
The idea is to get a cheap alternative to a professional (expensive) CO meter for use when setting the mixture on cars without oxygen sensors.Such as my K Jet
equipped 740se (UK model)
I appreciate the need to heat the sensor but would have thought this was not an insurmountable problem.
Probably yet another of my many failed ideas to save money!
Just thought it would be an idea to run it past our FI gurus on the board.
Thanks for any feedback Colin.

Thank you all for your help/ideas.
Yes I have used the colortune many years ago and it was quite good but did not replace all spark plug types and in some engines with the plugs down long tunnels, impossible to see!
What I was tring to achieve was a tool to use on any car by putting it up the exhaust pipe.

No, my 1990 740 B200e has no cat or oxygen sensor (less expensive bits to go wrong) + plain old K Jet injection (CIS) as a result it manages 119 bhp from a smaller bore B230 of only 2 litres, not a lot, but just about adequate with a 5 speed manual box and giving just over 30mpg average, with fuel at £0.72/litre it needs too!

Might get a used sensor + boss an weld it into front exhaust when it`s changed.
Autospeed site well worth a look.

Thanks again, Colin.

There is a lot of info at this address, more than just O2 sensors.

http://www.autospeed.com/A_0618/page1.html

Funny you should ask that!
I *just* bought a kit air/fuel mixture meter.... From my place of work. "Silicon chips" magazine produces it. It cost me 55 aussie dollars. Cheap enough! It doesn't do CO though, but does the idle air mixture, so i assume it's a similar thing. It doens't need to heat the sensor, all it does is tap into the existing lines for the Oxygen sensor. You say your's doesn't have an oxygen sensor? I thought it had to being a 1990 model, anyways, just go to a wrecker, pick up a bosch sensor that will fit the screw thread in front of your catalytic convertor, then you just calibrate your own meter (after you use a +12 v supply to heat it!) anyways, Ciao, might start the kit!
Az

For many purposes the Gunson ColorTune is pretty good at reading mixture.
It is a spark plug with a window in it so that you can see the color of
the flame. It is like a gas burner - yellow or white is too rich, bluish
green just about right and purplish-blue is too lean.
--
George Downs Bartlesville, Oklahoma

If I understand what you want correctly, these are quite common. In North America, Autometer sell them, as well as Cyberdyne, Haltech and K&N (the air filter guys). My personal favorite is Dawes Devices' unit.
Do a search for his site in Google or such....