EGO voltages

[Bernd Felsche]

Jens Knickmeyer tapped away at the keyboard with:
> up to now, I thought I knew how an EGO works. But now
> I am not so sure....
> 
> I just took a look at my data logged on today's drive to France
> (took about 1 hour). I set up my data logger to log rpm, injection
> time, engine temp and lambda voltage. Note that all data is not
> measured by seperate measurement equipment but I receive data
> directly from the ECU by using K-Line communication. Looking at
> lambda voltage, I recognized that the ECU sometimes tells a value
> of 1.85V. AFAIK, lambda voltage is limited by approx. [0.1V,
> 0.85V]. I tried to recognize any correlation between lambda
> voltage and any other signal, but I couldn't. The 1.85V occurr
> instead of the 0.85V I would have expected. The "lean" voltage of
> 0.1V is reached in every cycle, no problem there.

1.1V is about the maximum lambda voltage. 1.85 is way off-scale.

> My questions:
> Is there any chance that an EGO produces such a high voltage (which
> would indicate "ultramegahyperrich" mixture)?
> Can anyone imagine a defect which results in such a high lambda voltage?
> Can an interference with other substances/gases produce such a high
> voltage?

The high voltage could be because of a bad chassis connection at the
lambda probe. Single- and three-wire sensors are susceptible as they
don't carry a signal ground in the loom to the sensor, relying
instead on electrical contact of the exhaust manifold.

Check this by starting the engine and measuring the voltage from
battery negative to manifold.  You should see only a few millivolts
from noise.  Anything more than 100mV as a baseline and you need to
investigate.

See if the voltages get to be more sensible after you add a ground
strap from the exhaust manifold to the engine. (Use a jumper cable
and clamp it firmly.) Also, make sure that the engine has a secure
connection to battery negative. Give each of the wires a tug to make
sure it doesn't just _look_ OK.

-- 
Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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