Code P0304 (spark plug and COP already replaced – reset code and still have a miss on 4 cylinder.

ANSWER : If the fault is now pinned down to one cylinder, a possibility is a faulty fuel injector. Faults can be of various sorts: injector leaks, the injector driver in the ECM, the injector itself in terms of the electrical solenoid/circuit. But, there are other possibilities and all will have to be tracked down until the fault is found: Faulty oxygen sensor(s); Burned exhaust valve; Faulty catalytic converter(s); Poor compression in that cylinder; Defective computer (rare). To get this resolved, the recommended service is a misfiring diagnostic. If you request that service, the responding certified mechanic will get this diagnosed and resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.

ANSWER : Hi there. Your issue might be caused by a faulty O2 sensor. You might want to read this article about the P0174 OBD-II trouble code as it will show you possible causes, symptoms and solutions to resolve the problems.

ANSWER : Hi there. Try using a pair of small needle nose pliers to pull off the rubber boots from the spark plugs. As you pull, twist the rubber boots to break them free. If you cannot get the rubber boots off, then try using some mineral oil on the boots to aid them off, then clean off the oil with soap and water with degreaser. If you need further assistance with removing the boots from the spark plugs, then seek out a professional, such as one from Your Mechanic, to help you.

ANSWER : The P0304 code indicates a misfire has been detected on cylinder 4. The P0172 code indicates that the fuel mixture is richer than the mixture control can compensate for. It’s possible that they are related, but not necessarily. Rich mixture can be caused by excessive fuel pressure, or sometimes by leakage at a fuel injector. If your misfire is caused by leakage at injector number four, then it’s likely that the two codes have a common cause. It’s also possible that you have had a spark plug foul because of a rich mixture. Again, that would be a common cause. But it is also possible that you have a failure in the number four ignition coil, they are not uncommon. In that case, the P0172 would be a separate issue altogether. If I were working on the car, I would try to determine the cause of the over rich mixture and then work from there. In any case, you need to have a qualified technician check this thing out. Contact Your Mechanic and they can send a technician to your home or office to check out your car and tell you what needs to be done.

ANSWER : Hi there. Based on what you’ve described, this could be a combination of faults between 2 or more things; however, I don’t believe the coils and spark plugs are at fault. One of the codes is set during a low fuel misfire (lean condition), one is specifying a misfire on cylinder 4, and one is a turbo related code; all based on a generic code investigation.

The make and model of the vehicle helps, but is not necessary at the moment. When a low fuel pressure misfire is set, there is a lean condition that has been detected by the sensors and one of the codes is telling us in which cylinder this is occurring. A possibility is a restricted fuel injector, loose injector harness, poor pin fit in the wire harness, and an air leak near that cylinder’s port in the intake manifold.

I’m leaning more towards a leak or crack somewhere creating an air leak since we also have a turbo related code stored and an intermittent rough start when cold. I strongly suggest having a qualified technician perform an inspection to determine the root cause. YourMechanic has several available technicians that can assist you with a Check Engine Light inspection and determine exactly what is giving rise to codes P0313, P0299, and P0304.

ANSWER : Hello there, many faults will cause your 1988 Ford Contour to have a misfire even after the spark plugs were replaced. When oil is seen on the spark plug this indicates that the valve cover is leaking onto the plugs. When this happens it fouls the plugs and can cause a misfire. Until the oil leak is addressed the spark plugs will continue to become fouled. If the misfire persists there are many potential causes such as the plug wires, fuel pump, vacuum leak, oxygen sensor, MAF sensor, or the cap & rotor. A qualified Technician such as one from YourMechanic will be able to diagnose your misfire fault and make any repairs required to resolve the issue.

ANSWER : If the spark plugs hadn’t been changed until 130k, it was time for the to be replaced anyway. This is probably why the dealer went with that repair as worn spark plugs can cause misfires. Ignition coils are another part that may fail and cause misfires when they malfunction. A compression test and cylinder leak-down test will show if there is a problem with the valves. You can try having the coils replaced and the valves adjusted by the dealer. Consider hiring an experienced technician like one from YourMechanic who can come out and conduct the same tests as the dealer could and determine the cause for your check engine light.

ANSWER : You have a problem with the distributor assembly. I recommend replacing the distributor assembly. This will replace all the possible sensors and coil for the ignition and fix the problem you have.