Re: Bad O2 sensor / high fuel consumption?

[Igor Kessel <four_rings@worldnet.att.net>]

"Iain Atkinson (ETL)" wrote:
> 
> Hi Igor
> 
> You are right 15w50 is not available commercially over in the UK, I use the VAG Synta Gold fully synthetic, it's cheaper than Mobil 1 for a larger quantity, this is what Phil and the UK club recommend as well, judging from other peoples opinion I think the consumption is about right. Any other ways to detect a bad sensor?

Iain,
the only way known to me would be to observe the swing of tension on the
sensor itself. The older it gets, the lower the frequency becomes.

The O2 sensor is an active element, i.e. it produces tension (0 to 1v,
with 0.5v corresponding with the stoichometric 14.7:1 air to fuel
ratio). It's similar to a thermocouple in operation and is comprised, if
memory does not betray me here, out of a Pt wire coated with some Rare
Earth element.

If you want to measure this tension, actually its first derivative,
you're in a catch-22:
To observe the swing rate you need an old style analogue voltmeter. The
trouble is, it's impedance is waaaay too low, in the neighbourhood of
units of megaohms if not hundreds of kiloohms and it _will_ shunt out
the O2 sensor rendering it inoperable and the CIS will go open open loop
to a default map.

You could use a digital voltmeter with the input impedance of hundreds
of megaohms but the rate of change would be smeared by the jumping
digits.

You could use one of the expensive engineering multimeters like my
Wavetech 2000 or a Fluke 83/85/87 which have a moving LCD bar at the
bottom of the display. They also have the indispensable frequency and
duty cycle measuring capability.

When I want to measure time and/or frequency or duty cycle very
accurately I fire up my Tektronix oscilloscope.

You could also use one of the so-called Lambda meters as a crude
indicator. I designed and built my own coz wanted the 30-LED resolution
but the regular 10-LED ones are widely available commercially.

You could see a picture of mine at:
http://www.geocities.com/MotorCity/Garage/8949/homepage.html
it's in the leftmost corner of the torpedo, between the boost gauge and
the A-pillar.

-- 
Igor Kessel
Two turbo quattros.