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Strange ignition problem


My car (Coupe GT 85) has been getting harder and harder to start.
I cleaned it up and changed the spark plugs, but still it's hard to start.
I then did all the test in the manual, coil ok, hall sender ok, ignition
control unit ok. These are tests with the ignition on and checking the
voltages at the coil and ignition control unit(small 7 pin device that
bolts to a heatsink) and turning the crank(manually) and watching the hall
sender work, grounding the middle pin from the hall sender and watching the
voltage rise at the primary coil. All these static tests worked fine.

Now here is the strange thing: 
When you try to start the engine(and have a spark plug removed to check the spark)
there might be one spark when you start cranking, but no sparks after that
until you let go of the ignition key, then there are few more sparks. 
Put spark plug back in, check primary coil winding, same effect no voltage
during cranking but a few when you stop as the motor turns under its own momentum.
Check hall sender (at the ignition control) this seems to be working during 
cranking but I can't be certain as it is hard to read my digital meter 
under these conditions(~AC).	

Normally the car will start with the first spark, or when you let go of
the ignition key. Sometimes it floods, then a small push start gets it running fine.
Once the car is running it's fine, it's just that it doesn't spark while
cranking???? It is as if the relay that cuts the power to the lights is also
some how cutting the power for the spark. Could it be the ignition switch/key?

At the moment I suspect the ignition control unit.

Any suggestions?