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PO300 - PO303 codes..... Multiple misfire and #3 cylinder misfire..
System pump motor..... and Supply Low Voltage ( Put new battery in to solve this problem).Engine was knocking, found that the Wife ran car with 3 quarts low for I don't know how long. Changed oil to solve that problem.... ( The engine runs well for the first minute or so and then goes to knocking) Engine was still Knocking.. Changed coil on#3 cyl. knocking still. unplugged #3 cyl , engine ran the same. Plugged in #3 cyl and unplugged the other cylinders one at a time and the engine ran worse each time. Exchanged #3 and #2 coil and repeated procedure. Engine ran the same with #3 unplugged. This tells there is a problem with #3 cyl. So I changed #3 spark plug and result was the same. Next I pulled the injectors and swapped #3 and #2. put injectors on and went through procedure with coils again. Engine runs the same with #3 unplugged and worse when any of the other cylinders are unplugged while #3 is plugged in. Help me please!!!!!
 

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Update....The #3 driver in the ECM was bad. Had to get another ECM but, now I have to take it to the dealership to have the ECM reprogramed to my Jeep. We will see how that goes.
 
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