Re: V8 Gearboxes & O2 Sensor

[Steve Manning <stephenm@ix.netcom.com>]

At 03:51 PM 5/27/96 EDT, Philip Ross wrote:
(snip)
>I have been interested to read all the comments about the 02 sensor and #5 fuse
>on the V8.  I have just picked up our V8 from the main London Audi dealer
with a
>surging problem supposedly fixed by cleaning the throttle switch - however the
>problem still exists.  When you are going along at a steady speed on the
>motorway (say with the cruise control set at 90mph) you can feel the engine
>pulsing as if the amount of fuel being supplied to the engine is being varied,
>although the speed does not fluctuate.  You can also see the instant MPG
jumping
>up and down apparently in time with the pulsing of the engine.  I also find
that
>when accelerating in the car that it seems to go in bursts rather than a steady
>rise in power and revs.
>
>The London garage assured me that the O2 sensor was fine and that there was
>nothing wrong with the car according to their computer.  I am not convinced the
>O2 sensor is OK and suspect it is faulty causing the ECU to vary the amount of
>fuel incorrectly.  Today I removed the #5 (O2 sensor) fuse for a few miles on
>the motorway and the car did not drive any worse which suggests to me that the
>O2 sensor must be faulty.  Am I right?  Is replacement the only option?  How
>much are they?

I would still change your O2 sensor...your symptoms are exactly what I and
others solved by replacing it (mine needed replacing about every 30k miles).
And the computer would NOT detect a fault; the computer only detects 'no
signal' or 'signal out of range' which would not be the case with a flaky or
erratic sensor.

Another 'real-life' O2 sensor test I used to make would be to accelerate to
highway speed, then floor it in 5th.  Since the O2 sensor is cut out at full
throttle, you could tell it was the problem if you accelerated smoothly
away, but surged at anything less than full throttle.

'Generic' 3-wire O2 sensors are around $100/US; ones w/the attached plugs
range up to $200/US at the dealer, less from others.  If you want to change
it yourself (it is easy) and want any help on directions let me
know............SLM

Steve Manning:	stephenm@ix.netcom.com (Metro D.C. area, USA)
	Mopar:	'67 & '68 Plymouth Furys (big blocks)
		'70 Barracuda convertible (small block)
		'87 GLHS (tiny block)
	Audi:	Two '88 90Q's (built on the same day)
	Misc:	'73 Ford Country Squire wagon (daily driver!); other stuff...