Why is my check engine light coming on

The flashing Check Engine light means way too much raw fuel is entering the exhaust system and the catalytic converter is going to overheat and be damaged. That's a very expensive repair. The rough running suggests a misfire which can send raw unburned fuel into the exhaust and is likely related. Once the Check Engine light turned on, there will be a diagnostic fault code stored in the Engine Computer. Having that code read is the place to start. Many auto parts stores will do that for you for free. Codes never say to replace parts. They indicate the circuit or system that needs further diagnosis.

You can treat your own illness but we pay doctors to figure out what's wrong. Same thing with cars. Unless you want to go through all the ongoing training mechanics go through, it's less expensive and more effective to have this kind of problem professionally diagnosed. Way too often I read that someone has come here for help after "trying" a dozen parts that didn't help.

We love helping do-it-yourselfers fix their own cars and I really respect anyone who wants to learn, (about anything, not just cars), but you have to provide a starting point so we know which direction to send you. We need you to tell us the same things a mechanic would learn from looking at and listening to your car. You also have to be able to perform the tests a mechanic would perform and relay the results of those tests back to us. So far the best advice I can provide is that there has to be a stored diagnostic fault code since the Check Engine light came on. Chrysler is very good about that. Some cars have Check Engine lights that turn on when the computer is "keeping an eye" on a developing problem but it hasn't set a code yet. That doesn't do any good. With Chrysler products there will be a code in memory unless the battery was disconnected or run dead, then that valuable information will have been lost.

If you cycled the ignition switch to get the codes, that only checks the Engine Computer, not any of the many other computers. A scanner is needed to access the other ones. Is it possible a code was displayed too quickly and you missed it when it continued on to "done"? I'd go to an auto parts store and have them use a code reader. At the very least, there should a misfire code that will tell you which cylinder is causing the problem. If by some odd chance there is no code, a full scanner will be needed to view live data to see the sensor data the Engine Computer is seeing.

You need air, fuel, compression, and spark for a cylinder to make power. When the problem is intermittent, a compression problem is very unlikely since mechanical things that break don't magically fix themselves. Chrysler has extremely little trouble with fuel injectors so that should be one of the last things to suspect. If there is a reason to suspect an injector, a common approach is to switch it with one from a different cylinder, then see if that other cylinder develops a misfire. If it does, replace the injector.

Air is common to all the cylinders. A problem there is rare and would cause different symptoms. That leaves spark as the main suspect.

The spark plug is only one part of the system. The ignition coil and spark plug wire also have to be considered. The coil is actually two coils in one "coil pack". Each coil fires two spark plugs at the same time. Typically when the coil fails, two plugs won't fire and the engine will have very little power. You can try switching two spark plug wires to see if a different cylinder sets a misfire code, but with all the running around to have fault codes read, this is one time it makes more sense to just "throw random parts at the problem". Normally that's the least efficient and most costly approach but when you have so few parts to guess at, AND since they are common maintenance items anyway, I'd suggest replacing all of the spark plugs and all of the spark plug wires. When one shoe is worn out, you buy two new shoes, right? When your sock gets a hole in it, you don't just buy one new sock. It's not practical to replace one spark plug, other than as a test, and leave in the others that are just as old and worn.

The cost of new spark plugs and wires is relatively low, and since the chance of solving the problem is so high, it makes more sense to start with that before paying for your mechanic's time. If the problem is still there, at least you will have saved your mechanic the time and expense of replacing those parts. He can move on right away to the more involved tests and diagnosis.