[V8] power drop outs

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Fri Apr 6 16:18:43 EDT 2007

... as has been discussed here at length in the past ... there is an
implied fourth wire in the OXS circuit ... that being a ground which is
provided from the OXS to the reference point the ECU has on the engine
block through the crossover pipe and exhaust manifolds.  This is the
benefit of the sensors with 4 wires, you don't have to depend on the
manifolds to carry sensitive signals ... but it turns out that if you're
not careful in your selection of a ground point for the 4 wire sensor
you can do more harm than good.  

I consider neither of the heater wires on an OXS to be connected to any
other signal or ground point ... that is to say, you should be able to
take a meg-ohmmeter and measure the resistance from the case of the OXS
to both heater lines and see infinite resistance.  This is why both
wires are the same color ... either one can be connected to power or

Based on your description Mike, I suspect that the heater in the OXS you
have has failed in a way so that it is now connected to either the
ground or signal line of the OXS.  There is some chance that a bad
ground from the crossover pipe to the engine block may be or may be
contributing your problem, but I think that's a long shot.  

I think that if you do as you plan ... that is to replace the OXS ... it
will resolve the problem you're seeing with the OXS voltage, and it will
likely help with the rough running after the engine runs from cold.  I'm
not 100% sure it explains your intermittent power loss, but the OXS
certainly appears to be something that needs to be fixed.  

BTW, if you wanted to create a pseudo 4-wire set up with the stock
sender you can run a dedicated ground wire from the ground lug on the
block and either a ring lug large enough to go around the OXS threads or
to a self tapping screw into the crossover assembly.  I'm thinking you
could drill a hole in the structure of the crossover that is not part of
the exhaust piping.  If I were to do this, I'd probably also use a star
washer between the ring lug and the self tapping screw to ensure a good
electrical connection.

Steve B
San Jose, CA (USA)
> To clarify, when checking the voltage out put of the signal wire (not
> or Neg) I was seeing 3-10V!  Obviously something was/is not right with
> 02.  I suppose I can try to run without it to see if when warm the
> go away.  I could also run without the power leads attached as the 02
> reach operating temp though it will take more time and then measure
> voltage.  The only way for me to see that kind of high volt output is
> the + from the harness is shorting inside the 02.
> I can't imagine what that kind of issues having that level of voltage
> into the ecu from the 02 lead might cause.  Any usual suspects for MAF
> leaks?
> OK Mike, I'm a little confused by your note...
> There are usually three wires on an O2 sensor.  1) Power to the heater
> (+12), 2) ground, and 3) Output from the sensor (0 to 1 volt).
> If the car doesn't straighten up when the 02 is disconnected, suspect
> temp sensor, MAF, intake air leaks after the MAF, or a leaking

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