Several problems may cause your Plymouth Neon cylinders to misfire. The problem could be located in the ignition secondary system, carburetor, fuel injection or even the exhaust gas recirculation (EGR) system. Here we will look at the most common sources of cylinder misfire to guide you in finding the particular problem in your engine.
Check the EGR valve. Make sure the valve is opening and closing. It is common for the valve to stick in the open position and cause the engine to misfire during idle. Warm up the engine; then, working from the engine compartment, rev up the engine by pulling the accelerator linkage by hand as you observe the stem inside the EGR valve. If it does not move, the EGR might need cleaning or replacement.
Check the idle circuit on your carburetor if you have this system on your vehicle. Dirt and other contaminants may clog the idle circuit, requiring a good cleaning job.
Inspect the fuel injectors if your vehicle comes equipped with a multiport fuel injection system. You can use an automotive stethoscope or a rubber hose of proper length to verify the injectors are operating properly. If you use a hose, place one end of the hose against the injector's body and the other end against you ear. You should be able to hear a clicking sound as the injector's valve opens and closes. If you do not hear this sound, suspect the injector.
Examine the secondary system components. Remove and clean the plugs if they are fouled with oil or carbon deposits using a wire brush. Double check the spark plug gap using a wire feeler gauge and make sure it is correct. Check the spark plug wires for wear, corrosion and condition of boot, metal terminals and wire insulator. Inspect the distributor cap for cracks, carbon deposits and condition of the terminals. Worn or defective components weaken or block a good spark and cause the cylinder to misfire.
Look for the vehicle emission label at the front or side of the engine compartment. The label contains a vacuum diagram, ignition system and timing information. Use the vacuum diagram to check every single hose and make sure all are properly connected and in good condition. A vacuum leak may cause the engine to misfire as well.
Verify the engine fuel-mixture. Too much air---compared to fuel---injected into the cylinder may cause it to misfire too. You might need a code reader or scan diagnostic tool to extract the computer trouble codes from the engine to get a bad fuel mixture diagnostic. If you are not familiar with these tools, you may take your car to an auto shop to perform this diagnostic.
