O2 Sensors query

[classicdat]

I know this forum is dominated by those of us into Old School and carbs mainly.
Recently I have branched out into Fuel injection and am learning about their inner workings. Testing my O2 sensor I have found that it gives out a -ve voltage when my car is running on LPG.
Does anyone have any idea why an O2 sensor would give a -ve reading? It is a later model sensor with 4 wires but still over 10 years old.
Any suggestions appreciated, (hopefully)
Vaughan

[DAT620]

swap the wires over on your voltmeter ?

[classicdat]

Nah, reads fine on petrol, when I switch it varies, dipping into the -ves. Not a constant -ve voltage, but dipping into the -ves non the less, which is beyond me.

[unlimitedpower]

O2 sensors are tested via ohms rather than voltage.
A working O2 sensor will alternate up and down very very quickly i would expect faster than a muilty meter can cope with.
I know its quicker than my old laptop could cope with when i installed the new one in my primera wagon.

Id say with the LPG it might be showing more learn ratios compared to the petrol so could be spending more time lower on the voltage scale.
But i could be way way off on that so by no means take what i say as gospel.

[Bartman]

Getting a bit ot, but what is stoich for lpg?

[DAT620]

took a bit of searching
"LPG provides about 8% more energy per unit weight (LHV = 19,757
BTU/lbm) than gasoline. Theoretically, vehicle operation with LPG
should be more efficient than with gasoline, i.e., the vehicle should
attain better specific fuel consumption and improved mileage. However,
this will only happen if the engine design is optimized for LPG fuel.
If a gasoline engine is converted to operate on LPG this increased
efficiency will not be realized due to the lower density of LPG
compared to gasoline and also its slightly higher oxygen demand (LPG
stoichiometric A/F = 15.8). The lighter density fuel displaces air in
the intake manifold, and thus, less air per cycle is induced to the
cylinders. This translates to a decreased volumetric efficiency and a
loss of power compared to the original gasoline rating of the engine."

[Bartman]

Thats quite lean.

[classicdat]

Thanx J, appreciate the time you have taken. My testing was to check mixture, not the O2 sensor. Reading what you have added suggests that my running lean issue is aggravated by the low density of LPG. I will get fiddling with the regulator, funny thing is since I have threatened to do something she has run well. Still can't work out why it generates at -Ve voltage.