Hmmm. This is definitely not common, but it sounds like the Engine Computer might be defective. The ASD relay is working correctly. When the computer gets pulses from the crankshaft position sensor and the camshaft position sensor, it turns on the ASD relay. That relay is what sends voltage to the coil pack, injectors, etc. When you stop cranking the engine, those sensor pulses stop, then the computer turns off the ASD relay as you heard it do.
Before you go looking for a computer, it might be a good idea to find a mechanic with the Chrysler DRB3 scanner to read live sensor data. In particular, it will list the cam and crank sensors as "no" or "present" while you're cranking the engine. If one is switching back and forth, you may just have a bad sensor. All it takes is one weak pulse every couple of seconds to keep the ASD relay turned on, but that's not sufficient to fire a coil. Some aftermarket scanners will read those sensors too.
As for that one spark, the computer keeps the coil grounded so it builds up a nice big magnetic field, then when the pulses come from the sensors, the computer switches the ground side open to stop current flow. The rapidly collapsing magnetic field is what induces the very high voltage to the spark plug. When you stop cranking the engine, the ASD relay turning off also breaks the circuit, (the feed side instead of the ground side, but that doesn't matter), so the magnetic field collapses again and makes that one spark. That tells us the computer is not switching the ground side and is why there isn't any spark from the coil during cranking.
Monday, January 31st, 2011 AT 11:09 PM