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What OXY voltage?

Nathan Pryor

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Hi Ashley I have a narrow band oxy installed. The car is still on a base map before a proper tune. I want to road test the vehicle to check brakes etc. When I am giving it a bit of pedal what sort of oxy voltage should I see? At the moment it hangs around 0.4 - 0.6 volts at idle and no load rpm. I see from the book it should be at 0.8 in a perfect world. At what point (voltage) is the average vehicle considered to be in the lean zone? (For protection of my engine) Can the voltage be converted to a ratio? If so, whats the formula? Thanks Nathan

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Here are some typical voltages for certain AFR's...

< 0.6 V  =  >15:1   (lean)

0.72 V   =  14:1

0.84 V   =  13:1

0.86 V   =  12:1

0.88 V   =  11:1  (rich)

As you can see, there is very little voltage change between a little bit rich and a lot rich, and there is also no voltage change between lean and very lean.  These sensors were only ever designed to measure the stoichiometric AFR of 14.7:1 (best for emissions).  They are used to optimise the exhaust gas for the catalytic converter.  If you are worried about the protection of your engine, best take it to get tuned, then worry about testing the brakes.  DO NOT run the engine under power until it is properly tuned, chances are it will be too lean and have too much timing which could cause an instant blow up!

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