Re: resistor inline with O2 sensor

[Rob Ellis <aellis@xxxxxxxxxxxxxxxx>]

> A resistor inline with the O2 sensor is a common mod that does work on
> pre-OBD cars.  It is a value used to make the fine adjustments in
> mixture above the initial mixture resulting from the baseline values
> The ECU can run the engine in fully warm mode, just thinks that it needs
> a richer mixture than it really does.  So you can get a mixture in the
> 13.x range rather than the 14.7 which kees the EPA happy, but not max power.

To be clear about this, any resistors used to modify the signal from the
O2 sensor would need to be set up as a voltage divider (you need 2
resistors) to obtain a useful result.  Putting a single resistor inline
with the O2 signal wire will ONLY result in lower current being sent to
the computer (as pointed out by a previous post) and will most likely
make no difference.

The signal from the O2 sensor is a voltage between 0 and 1V, higher
voltage means the mixture is richer.  Normally the average value is around
0.45-0.47V or so.  You could "fool" the computer into thinking you were
running lean by dividing down the voltage (using the simple voltage
divider mentioned above), to say 0.40V, so the computer would give a bit
more gas to compensate.

However, there are better (and easier) ways to do this... for example,
adjusting the tension on the AFM flap by a few notches will give you a
nice, fine adjustment of the fuel mixture (at least on older cars, like
my E30).

Rob
'89 325i

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