Date: Tue, 14 Jan 2003 15:22:25 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: O2 sensor testing
In-Reply-To: <3E2449FA.6010802@charter.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 12:33 PM 1/14/2003, John Rodgers wrote:
>When disconnected, failed, removed, cut wires, whatever,
Only if it results in an open circuit. If it goes to ground the ECU will
drive the system full rich -- and if it goes high (or example from leakage
from the heater wires on the 2.1s) the ECU may very well lean the system
out considerably -- I'm not sure sure how smart it is about noticing that a
3-volt (say) output is not possible from an operating O2 sensor.
> the ECU goes to open loop and the engine will run rich.
This depends on how the system is adjusted -- if the other control
components (ignition, fuel pressure regulator, AFM, maybe TI and TII
sensors) are correct the engine should run perfectly well for every purpose
*except* low emissions. If the mixture strays a tiny bit one way the NOx
will rise sharply, and if it strays a tiny bit the other way the CO (and
maybe hydrocarbons?) will rise. But these effects are so sensitive that
they will happen long before the mixture reaches either the best-economy
mixture going lean, or the best-power mixture going rich. These systems
are designed to run perfectly acceptably -- from a performance standpoint
-- without an O2 sensor, and until unleaded gas became widely available in
Europe that's how all the European FI systems were. My own ('84,
California-spec) van was delivered in Germany with no sensor and a straight
pipe in place of the cat, since both would have been destroyed by the first
tank or two of leaded gas -- and ran that way in Scotland for about 90,000
miles before coming here and having those pieces installed, along with the
by-then redundant restricted filler neck. For most of that time the OXS
light was lit because the local dealers had no idea how to reset it.
I'm not saying that people should run without the sensor -- it *is*
required to balance the mixture closely enough for the cat to operate
correctly, and it will backstop the other systems and provide a correct
mixture even when they are not fully correct. But there are an awful lot
of them out there running that way, because that's how they were delivered
from the factory. When I was in Scotland in '91 or so, unleaded gas was
cheaper than leaded to encourage its use (10p a liter maybe?), but I don't
think that even then it was universally available.
david
--
David Beierl -- dbeierl@attglobal.net
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