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Re: Ignition Timing
Posted by Stottler (more from Stottler) on Sun, 22 Dec 2002 22:12:30
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

I haven't looked at a 2.0L 9000 in a while, but in the few modern engines
that have a 'distributor' it no longer has a timing function; it is just a
'high voltage switch' directing the spark to the right plug wire.  The base
timing is set by the machined hole in the engine block that holds the
crankshaft position sensor.  So, the spark is timed by crankshaft position,
not by distributor position.  You will not get any effect from turning the
distributor unless you turn it far enough to direct the spark to the next
(wrong) wire at which point the engine will stop.   So, there is no longer
any base timing adjustment - the computer controls it all based on crank
position.  Often, spark timing is used to control idle speed as well since
varying spark timing changes engine torque much more quickly than bleeding
air into the inlet, so in many engines you will see spark timing varying at
idle.  Also, pretty much all modern engines have knock detection/control
systems which detect detonation/spark knock and adjust the ignition timing
accordingly, so, again, there should be no need to adjust the timing.
During normal engine operation, spark timing is controlled by the computer
based on engine speed, airflow, temperature, altitude, manifold pressure,
etc.  Also, sometimes ignition timing is retarded during a transmission
shift (automatic and/or manual) to momentarily reduce torque and reduce
clutchpack wear in automatics and reduce speed flares in manual trans
applications.  Probably more background than you wanted - why did you want
to try to adjust the timing?

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