Does it miss all the time? Hot and cold? Under acceleration? deceleration?
Hello!
New Expert here!
Try looking for vacuum leaks along the intake manifold gasket right by number 3 and 4 cylinder. THis is very common and can cause misfires at idle.
If there are no vacuum leaks, Lets go ahead and check the fuel injectors. You can ohm them out with an ohm meter. Also, lets be sure that the fuel injectors on those cylinders are getting a signal from the computer to fire. You can use a test light or a noid light to check this.
Let me know!
All of them are pulsing?
WHat does number 4 injector ohm out at?
Ok... Good!
DO you have access to a scanner that can read live data?
If you have access to a scanner that can read data and fuel trims and things like that, check freeze frame and see when the misfires occurred. If it was at idle, then maybe you do have a vacuum leak.
There s also a TSB that explains there is a PCM re flash for these codes. However, you are experiencing a rough running so I don't think that TSB applies.
P0303 Cylinder 3 Misfire Detected
Possible Causes
Base engine mechanical fault that affects only one cylinder Check for air leaks in the Air Induction system (e.g., in the intake manifold)Check for air leaks in the EGR system and in its related hoses and/or valveCheck for air leaks in the PCV system and in its related hoses and/or valveFuel delivery component problem that affects only one cylinder (e.g., a contaminated, dirty or sticking fuel injector)Ignition system fault (coil or plug) that affects only one cylinder
Tests/Procedures:
1. Check fuel pressure and volume.
2. Then check for carbon build up on the valves and seats.
3. Check spark output at the spark plug.
Potential Causes:
Fuel PumpSpark PlugSpark Plug WireCarbon Fouled Valves - Carbon build up on valves. Diagnostic Codes: P0303 and p0304
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ADVANCED LEVEL SPECIALIST