Pat,
In a sequentially fired fuel injection setup on a 4
stroke car, the computer needs to know whether a given
cylinder is on the compression stroke or the exhaust
stroke. Since the cam runs at 1/2 crank speed, it's a
convenient place to get this info.
Bank fired EFI does not require this, nor does
throttle body injection.
By the way, a guy on one of the Mustang lists swapped
the fuel injection harness connections around to see
what effect mistiming would have. There was very
little difference from the driver's point of view.
This would support the assertion that SEFI seems to
have greatest effect on exhaust emissions. The
manufacturers were forced to deploy it to meet tight
emissions and fuel economy regulations.
Also, most sensors have a biasing magnet inside, and
depend on signals generated by slots in the moving
iron/steel timing disk. Attaching a magnet to a timing
wheel is expensive, and failure prone, cutting timing
slots is cheap. Some use hall effect sensors, others
simple coils. To allow the ECM to sense TDC (or other
fixed point) there is usually a missing tooth or
double wide slot on the crank. The cam sensor usually
only needs one tooth/slot to work, giving a very broad
indication to the ECM that cylinder #1 is compressing
or exhausting. Perhaps that is what you are seeing?
Carter Shore
--- "Bowen, Patrick" <pbowen@intellinetics.com> wrote:
>
> While redoing the timing on my moms Park Ave with a
> 3.8 ltr I have run
> across a question. It has both a Cam sensor and a
> Crank sensor. I for the
> life of me cannot figure out why it needs both, as
> the information is
> directly related to the other. To further
> complicate the question, I have
> discovered that the magnet on the cam sprocket (that
> the cam sensor senses)
> fell off. Being covered in metal shavings I am
> assuming this happened a
> long time ago, yet the car still ran, and only
> recently started acting
> erratic. So if this was removed, and the car still
> ran, what is its
> purpose? If it is required to run, then how did it?
>
> By the way this is a distributorless ignition.
>
> Patrick Bowen - who is now thinking of how hard it
> would be to make a
> distributorless ignition for a spit.
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