Chrysler Repair: Chrysler 300 with no fire, spark coils, chrysler 300

Question
I have a 1999 Chrysler 300 that suddenly stopped running going down the street, no warning signs. I hear the fuel pump running and have pulled a plug and am getting no fire to plug. A friend brought his scanner/computer and hooked it up and there were no codes given. Any ideas as to why this vehicle would suddenly loose fire to plugs? Seems to me a main computer/controller board or something and if that is suspected, how do you diagnose this??

Thanks,
Craig

Answer
Hi Craig,
When you say you hear the fuel pump running I assume that you mean for about a second when you first turn the key to the 'run' position. But how about when you are cranking the engine? That would, if present, corroborate that the autoshutdown relay is being held closed which is necessary not only for fuel but also for power to run the spark coils. If that is indeed the case, then we have the issue of why no spark even though there is power to run the coils and evidentally the pcm is also getting sensor input to drive the sparks coils' pulsing.
If you can't be sure of the fuel pump's running when you are cranking it over you could try by-passing the asd relay with a temporary jump to close its circuit to the pump and the coils. So remove the relay and jump a wire from the front pin to the rear pin (D to B, if so-marked) which replicates a closed relay situation and should cause the fuel pump to run continuously. This is for test purposes only and should not be used beyond this purpose for safety reasons. Then see if the engine will start. If so then there is an issue with the pcm not wanting to activate the asd when you are cranking the engine which could be a sensor (which is weak but not so bad as to set a code) or the pcm itself (but I would expect there to be a code for that, but it too could be just marginal and not set a code).
If with the relay jumped the engine still won't start and you don't have spark, then you would want to check fuse S (20 amp). In fact you might want to do that the very first thing before jumping the asd relay. If that fuse is OK, then it is possible that the wire from the fuse to the plug harness is open, or  possible that one of two capacitors on either side bank of coils is shorting out (but that would usually blow the fuse S if so). Check the dark green/light green wire on any of the coils to see if it is showing 12V. If it is, then that part of the circuit is OK and you would need to focus on the driver wire of the coils to see if the pcm is pulsing them.
That may be best done with an oscilloscope, so hopefully we won't have to go there.
I hope these initall suggestions will reveal what has gone wrong.
Roland
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