Did you unplug the O2 sensor to see of that changes things?

On 11/12/08, Ben S <phlogiston420@gmail.com> wrote:
> i started having problems with my '86 westy while driving last
> weekend.  it was our second good rain of the season here in san
> francisco, and after an afternoon of wet driving, i experienced the
> following phenomenon: if i let the engine speed get below about 2k rpm
> (at load or at idle), the engine would start to run poorly.  it
> stalled out a couple times while i was idling at stoplights.  the
> strange thing is that each time the engine started to struggle, the
> coolant warning light would come on and flash.  then, if i revved up
> the engine, it would start running smoothly again and the light would
> go out.
>
> when i came back the next (dry sunny) afternoon and tried to start
> her, i got very little response--the engine was cranking nice and
> strong but hardly even sputtering or missing... just cranking and
> cranking.  eventually it started and i got home.  while i was driving
> the power seemed normal (no missing) as long as i kept the engine
> above 2k.  once i parked i started poking around in the engine.
> here's what i found:
>
> the heater in the crankcase breather hose was unplugged.  plugging it
> back in did not help.  the throttle switch was reading open circuit
> with the throttle closed.  i put a jumper wire in the connector to it
> (to simulate a closed switch because i was too lazy to adjust it) and
> this did not help either.  i tried unplugging the temp II sensor.
> this did not help.  i verified that the idle air controller was
> "vibrating" with the ignition switch on.  i checked the resistance of
> the air flow sensor and it was in spec.  i checked the resistance of
> the air temp sensor (same connector) and it was maybe a hundred ohms
> over the value given in bently for 68degF (ambient temp was 71deg
> according to my dash thermo).  primary and secondary dc resistance
> were also in spec on the ignition coil.
>
> my engine has 175k on the clock.  my ignition wires are the good bosch
> ones with oem connectors and have 51k miles on them.  spark plugs have
> about 15k miles.  i changed the cap & rotor when i did the wires.
> visual inspection showed visible pitting on the contact surface of the
> rotor.
>
> what kind of component failures would cause this kind of issue?  when
> i've had ignition system problems before (arcing from the wires or
> fouled plugs) the problems came on slowly and mainly manifested at
> high rpm... this problem appeared drastically and immediately with no
> warning.  i'm thinking it must be either the hall sensor or 02 sensor.
>  what's the best way to troubleshoot these without just throwing new
> parts at my engine??
>
> Ben.
>
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--
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Chris S.
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