Ahhh. When you have no spark, you're only half done. You must also check to see if the fuel pump is running while cranking the engine. Chrysler pumps can be kind of hard to hear so there are other ways to tell if the systems are turning on. You can pop the cover off the automatic shutdown (ASD) relay and watch the contact while a helper cranks the engine, or, if you have a test light or inexpensive digital voltmeter, there are a number of places you can measure. The easiest will probably be the dark green wire with orange stripe in the plug for the coil. The same wire feeds the injectors, fuel pump or pump relay, and alternator field. You can measure on either of the small terminals on the back of the alternator, but they can be a little hard to reach.
You should find 0 volts on all of those points until the ignition switch is turned on, then you'll see 12 volts for just one second, then it will go back to 0 volts. That proves the ASD relay is turning on and the Engine Computer has control of it. The important thing is the 12 volts must come back during engine rotation, (cranking or running). If it does not, besides the missing spark, you won't have fuel pressure and the injectors won't be firing either.
If you do find 12 volts to the coil during engine cranking, then you are right to be in the coil circuit, but it is much more common to have a failure of the camshaft position sensor or crankshaft position sensor. It's the pulses from those that tell the computer to turn on the ASD relay. Since they are inputs that are observed by the Engine Computer, it will set a diagnostic fault code and turn on the Check Engine light if the signal is missing from one of those sensors. The place to start is by reading any stored codes. You may be able to rent a code reader from some of the auto parts stores.
Thursday, September 9th, 2010 AT 1:11 AM