2008 caravan 4.0 liter. Threw code p0300 then p0303 misfire in cylinder 3. Replaced the coil pack for that cylinder, spark plug still looked good. It's still throwing the 303 code but now it's throwing a 0203 code, injector circuit malfunction #3. what does that mean? injector bad or more serious? car will run fine for awhile, then maybe about 30-45 mins it will run real rough but still drive. On short trips it's ok but stop the car and restart it runs rough but still drives. If it's an injector I don't mnd changing it, it's the circuit thing that has me guessing it's not, how would you go about fixing that?