Re: Tech (RANT) : O2 sensors

["Dave Ewing" <rabbit16v@prodigy.net>]

I have my O2 sensor disconnected because it runs like crap with it hooked
up.  I have replaced it once because I actually diagnosed it to be really
slow reacting and it still ran like crap.  I don't plan on leaving it that
way I just haven't had time to diagnose the system again.  I have, however,
a motronic system that I plan to install so I may not need to figure out why
the dumb CIS-E system is not running optimally but I probably will since it
would bother me not knowing.  The thing is that I have replaced just about
everything in that system and it is still giving me problems.

As far as the euro systems are concerned, they are very simple.  They don't
have a F.I. computer since they are mechanical and use a warm-up regulator
on the side of the block, but they do have a knock box for the ignition
system.  I got a euro system from Australia (guy said the Scirocco came from
England and it was a 16v) and this is the system I got.  Now I cannot back
up the honesty of this guy but that is what arrived.

Lastly, I would like to say is that YES you can successfully disconnect your
02 sensor but I do not know (unless it is bad) that it will make your motor
perform better and not have any problems.  Yes, it won't run as efficiently
(whatever that means, I get 35 mpg out of my 2.0L 16v Rabbit with cams and
other mods) according to our state trained emissions tech at work, and it
may also burn out your cat prematurely (My car is a 77 so it is
non-catalyst--got the sticker in the jam too!!), but if efficiency isn't
your concern and you don't have a cat, then I guess you can play with the
idea. I have actually seen things on this subject on a couple different
places.  First, the oldest, is from the 'Volkswagen water-cooled front-wheel
drive performance handbook' by Greg Raven printed back in 1987 said that
"the Lambda sensor is a great watchdog that makes sure your motor is getting
the right amount of fuel.  If you unplug it, you will lose horsepower and
mileage.  The only reason you should defeat the Lambda sensor is if you need
to run leaded gas, at which time you must remove it and the cat to avoid
damaging those components".   Second, and the most informative comes from
'How to understand, service and modify Bosch fuel injection and engine
management' put out by Bentley in 1989 I believe, and updated in 1991.  This
will be long, so bear with me and learn!!!  This is what it says on the
Lambda sensor in chapter 7 paragraph 5.1  Systems with Lambda Sensors:

"The assumption is that, in most cases, street-driven cars which were
originally equipped with lambda sensors (and catlytic converters) are going
to retain them, both for legal (emissions and inspection) reasons, and
because of the driveability and fuel economy advantages - their ability to
continuously fine-tune the air-fuel misture to match different conditions.
The functional details of these systems are well covered in other parts of
this book.  In the context of high-performance modifications, however, there
are some important things to remember.

The basic fuel-injection system meters fuel to air in the best proportions
possible, based on its various inputs.  In closed-loop operation, the lambda
system monitors the exhaust and continuously makes additional fine
adjustment to the air-fuel warm-up when the lambda sensor is not yet up to
operating temperature and, in most systems, at full throttle when lambda
sensor control is bypassed in favor of a slightly enriched mixture.

Remember, even if the system is modified to make it capable of providing
more fuel, the lambda-sensor system in closed-loop operation will still do
just what it was designed to do - continuously djust the air fuel mixture to
approach the stoichiometric ratio, the narow range around alpha = 1.  In
short, no gain, except (maybe) in open-leep operation at full throttle.

Normally, this self-correcting capability - automatically keeping the
mixture near the perfect stoichiometric ratio - is very desirable.  If minor
system modifications make the mixture a little too ruch at low and mid-range
rpm, the lambda-sensor system in closed-loop operartion will tend to correct
back to the stoichiometric ratio and preserve driveability, exhaust
emissions control, and fuel economy.

The problems come when fuel system modifications force the system to the
limits of its normal range of adjustment - when the system which is
constantly sensing an over-rich mixture and constantly trying to adjust
morelean reaches the limits of its adjustment range.  In such a case, the
modifications and the resulting rich mixture will override the lambda
sensor's ability to correct, and will wreak havoc on the fuel economy,
driveability, and exhaust emissions".

Now all of this sounds great (both of the last two articles) but everyone
has to understand that the government does NOT want anyone to know that you
can disconnect emission parts on your car and make it run better.  So, most
publishers are not going to admit this IF it is true.  So, all of this is to
be taken with a grain of salt and a dash of independant thinking.  Remember,
my car gets 35mpg PLUS (if I don't drive it like a nascar everyday) with my
O2 sensor disconnected.  HTH, it better have it took me way too much time to
type that out!!!  Gotta get a scanner!!!

Dave
77 Rabbit 2.0L 16v
84 Scirocco


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