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First you need to retrieve codes from the Engine control module. You can buy a cheap code retriever at harbor freight and get the codes. After you get the codes, if it is P0301 it means cyl #1, P0302 = cyl #2, P0303=cyl 3 and P0304= cyl 4. For ex: if you got P0301 you should remove the ignition coil #1(near the front of the engine, where the pulley is) and change its position with the coil # 2. Also remove the spark plug #1 and change the position with the spark plug #4. Clear the codes and start and run the engine until the check engine light goes on. Check for codes and see if the code change for a different code. If it change the position observe which one is the change. If is P0304 you have a bad spark plug, If it is P0302 you have a bad coil. If it repeat P0301, you have either a low compression, bad injector/connector, bad intake gasket them you should continue your diagnostic. I hope this help you. Junior.
Might be dirty injector or burned valve. Check the connector on the injector. If good, run a compression test on all cylinders. If compression is significantly lower on #3, the head will have to come off. If compression is good, pull up the injector rail with injectors and wiring attached. Watch the injectors spray as someone cranks the engine.
P0300 is Multiple Misfire and P0303 is one specific misfire in the cyl #3.
A code P0303 may mean that one or more of the following has happened: * Faulty spark plug or wire * Faulty coil (pack) * Faulty oxygen sensor(s) * Faulty fuel injector * Burned exhaust valve * Faulty catalytic converter(s) * Running out of fuel * Poor compression * Defective computer
Possible Solutions: * If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back. * If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
coil packs very prone to failing... check compression for good readings (at least 100 - 120psi) if okay try new spark plug as these can fail under load and its the cheapest part to replace to eliminate. if misfire still present swap cylinder 3 coil with cylinder 1 coil and see if fault code moves to cylinder 1. hope this advice helps
2. Vacuum leak
3. Injector fault
4. High or low fuel pressure. Thats the list of things to check. This is a #3 cylinder misfire. There is also TSB about #3 injector needing added heat protection. This could definitely be the cause. I start at plugs and go from there. Hope this helps. Thank you, Lee
p303 is a cylinder 3 missfire I woul first check the coil and then the ingnition module, Then if this dont work you could have a bad injector. If after testing and still no fix you should check the compression in that cyl.