Date:         Fri, 12 Oct 2007 15:47:51 -0400
Reply-To:     "Daniel L. Katz" <katzd54@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Daniel L. Katz" <katzd54@YAHOO.COM>
Subject:      Re: Power loss when engine wet and cold

the o2 sensor itself IS vulnerable to water and other contaminants, such
as silcon compounds, and that is why they are shielded where they open to
the air.

for a simple 1 wire connection (signal wire only), it makes no difference
if, say, a crimp or soldered joint is wet. with a multi-wire plug, if it
was really soaked, there might, in theory, be a low grade short between
the signal wire and one of the others.

on some sensors, rather than an opening to the air (most likely where the
wires go), the source of ambient air is through the wire itself, and
therefore, it is important not to seal end of the wire at the closest
crimp with an anti-corrosion coating. also, unless marked sensor-safe,
silcon grease may be doubly hazardous - both sealing off ambient air and
potentially contaminating the sensor with silicon. contrary to popular
belief, wd40 is sensor safe - read the label.

a disconnected o2 sensor is irrelevant on cold starts, and normaly will
not cause stalling or really terrible operation otherwise.

a disconnected tempii sensor causes the ecu to "think" it is a bazillion
deg below zero, and therefore won't effect cold starts, but may make
starting tricky with a hot engine, although once started, it will run,
probably a bit rich.

dan



On Fri, 12 Oct 2007 09:19:33 -0700, dylan friedman <insyncro@YAHOO.COM>
wrote:

>What about stumbling at low RPM and smooth as silk at hi?
>
>
>
>Karl Mullendore <groups@WESTYVENTURES.COM> wrote: I've diagnosed two vans
with same symptoms, both Syncros on the trail,
>after splashing through puddles the OXS CONNECTOR and wire was soaked,
>the [small] change in the voltage reading caused by the moisture track
>caused the ECU to adjust the fuel mixture rich...loss of power and
>stumbling. I'm not a guesser or theorizer, but a experienced mechanic.
>The coolant temp sensor cannot be disconnected and the engine run
normally.
>
>Yes, shorted plug wires, especially the plug caps, will cause the
>symptom too, however weren't these replaced? And it would show up as a
>solid miss if so.
>
>Daniel L. Katz wrote:
>> richard:
>>
>> most obvious possibility is problem on high tension side of ignition,
such
>> as mositure and/or carbon tracks in distributor cap, arcing between
spark
>> plug wires and ground (might see sparks outright, or glow around wires,
at
>> night), or, even if not root cause, fouled plugs.
>>
>> O2 sensor very unlikely here, and it can be temporarily disconnected in
>> any case to eliminate possibility. ditto temp sensor. O2 sensor and,
>> though to a much lesser extent, temp sensor, are high impedence, low
>> current devices, so in this context a little contact resistance is
>> irrelevant.
>>
>> dan
>>
>>