Date: Tue, 5 Sep 2006 04:08:43 -0500
Reply-To: John Rodgers <inua@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@CHARTER.NET>
Subject: Re: Did the mechanic do something?
In-Reply-To: <44F64B7F.5050404@cox.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
This is something that has always bothered me, caused me concern,
especially since I burned a piston once - the burn-out went right
through the top of the piston.
Back in my flying days - and things have changed a lot since then - the
pilot could manually adjust the mixture for optimum performance based on
readings from the exhaust gas temperature (EGT) instrument. The first of
those instruments operated a lot like our O2 sensors - had a single
probe and used the average of all the cylinders for the reading. So it
was possible to have a cylinder that was whacked throwing off the EGT
reading a bit. Later on EGT's systems that had probes that read the
exhaust gas temperature for each individual cylinder. Then the pilot
could adjust fuel flow for the engine to the needs of the leanest
cylinder. This extended the life of the engine by extending the life of
the leanest cylinder. In other words, that lean cylinder didn't burn up
because the pilot could adjust fuel mixture by enriching it to the point
that it would run cooler This was an important advance in engine control
- you can't park an airplane on the hearest cloud when a cylinder burns
up in flight.
While the O2 sensor of the WBX is not an EGT sensor, it does send
signals to the ECU about the oxygen content of the exhaust, and the ECU
uses that to adjust fuel flow. Only thing is, on the WBX it's done all
at once. The ECU cannot fine tune the mixture of individual cylinders.
I don't know about newer engines, the Suburu and the like ........
perhaps they now have a way for the fuel/air mixture to be controlled
and fine tuned for each individual cylinder. If newer engines work that
way it will go a long way towards increased fuel economy and increasing
the life of the engine.
It would be a very cool thing to have an EGT system installed on a WBX
so the EGT could be read on each individual cylinder
Regards,
John Rodgers
88 GL Driver
Mark Drillock wrote:
> While there may be good reasons for checking the effect of disconnecting
> the oxygen sensor, the fact that an engine runs better with it unplugged
> in no way proves that anything is wrong with it or it's wiring.
>
> The oxygen sensor provides an exhaust gas feedback signal to the ECU but
> it can only see the combined gases of all 4 cylinders put together. If
> one cylinder is putting out a much different oxygen level than the other
> 3, this throws the combined reading off and the oxygen sensor signals
> this off reading to the ECU. The ECU may then attempt to correct this
> combined reading but can only do so by adjusting all 4 cylinders at
> once, even the 3 that were in fact working fine. This can result in an
> overall worse running engine than would be seen with a disconnected
> oxygen sensor in spite of the fact that the oxygen sensor was doing it's
> job properly.
>
> Mark
>
>
> Sam Walters wrote:
>
>> Charles,
>>
>> Attached are some files for assistance in diagnosis of fuel injection
>> system difficulties.
>>
>> Disconnect the O2 sensor and see if the problem goes away. If so, it is
>> either the O2 sensor or its wiring. You can run this way for a day or
>> two to compare. Wiggling the wire is no test of the O2 sensor.
>> ........................
>>
>>
>
>
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