test

[Shannen Durphey]

There is no crank sensor for many EFI or CCC'ed vehicles.  Everything is done
with the distributor.  The ecm "knows" that a reference pulse occurs at a
certain number of degrees before/after TDC by values contained in the eprom. 
The ecm then calculates a spark should occur a certain number of degrees BTDC
and converts degrees to time based on engine rpm.  The rotor position actually
determines which cylinder actually gets the spark.

The LT1 has slightly more complexity.  There are two signals generated by the
Opti-spark.  One is a high resolution 360 pulse/rev signal, one is a low
resolution signal with pulses of unequal size.  The ecm can determine when the
distributor is at TDC by counting the number of high resolution pulses occurring
during a given low resolution pulse.  After that, the ecm can determine a number
of degrees BTDC where spark should occur, convert the degrees to time based on
engine rpm, and fire the coil.  Again, the rotor position actually determines
which cylinder gets the spark.

The crank sensor on the 96 LT1/LT4 was added for misfire detection.  The engine
will start and run flawlessly with this sensor disconnected.  The sensor can
actually be used to estimate timing chain stretch by watching the scantool
displayed crankshaft offset values change while changing engine rpm.

Shannen

john wrote:
> 
> hi all how does a 95 L T 1 establish timing  there is no crank sensor
> 
> --
>     John McGuire
>  www.jbstreetrods.com
> john at jbstreetrods.com
> 
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