bad plug wire but no code???
Thread Starter
Joined: Dec 2003
Posts: 2,152
Likes: 0
From: Virginia Beach, Va
bad plug wire but no code??? is it possible to have a miss cuz of a bad or damaged wire without throwing a code? i feel a little jerk every few seconds at idle.....almost feels like a miss. ive narrowed it down to either a plug wire or the wire sheath beside the headers on the passenger side that goes to my front o2 sensor. any ideas?
Misfires need to exceed a certain threshold, for a while,
to set a SES code. But these misfires can be seen real-
time on a scanner and in this case you would be looking
for one cylinder that's higher than the "background" of
the rest. This pointed me right to my unseated Taylor
wire.
Bad wire insulation faults may only show up under load.
This being because the spark voltage takes the path of
least resistance (or rather, the spark-gap of least
breakover voltage). This voltage is set by the combined
insulation and air gap voltages, the air gap voltage
breakdown is proprtional to cylinder pressure inside.
So at idle / cruise, with pressure half atmospheric the
spark plug may still be the lowest arc point but when it
is at high cylinder pressure like WOT, the pinhole in your
plug wire sitting against the valve cover may present an
easier jump. And the situation there may change a lot
with a little road splash into the engine bay.
to set a SES code. But these misfires can be seen real-
time on a scanner and in this case you would be looking
for one cylinder that's higher than the "background" of
the rest. This pointed me right to my unseated Taylor
wire.
Bad wire insulation faults may only show up under load.
This being because the spark voltage takes the path of
least resistance (or rather, the spark-gap of least
breakover voltage). This voltage is set by the combined
insulation and air gap voltages, the air gap voltage
breakdown is proprtional to cylinder pressure inside.
So at idle / cruise, with pressure half atmospheric the
spark plug may still be the lowest arc point but when it
is at high cylinder pressure like WOT, the pinhole in your
plug wire sitting against the valve cover may present an
easier jump. And the situation there may change a lot
with a little road splash into the engine bay.
