![]() A failed ignition coil must be replaced in a 4-cylinder engine it's a fairly simple job. Once the problem is repaired or no longer detected, the misfiring code will clear itself after some driving.Ĭommon problems causing misfire codes P0300-P0308:įailed on-plug ignition coils are common in many cars, including BMW, Ford, Hyundai, Mazda, Nissan, Toyota, Volkswagen and GM. This can be checked by monitoring the crankshaft position sensor (CKP) or camshaft position sensor (CMP) signal with an oscilloscope read more here. Sometimes a broken or damaged tooth at the crankshaft or camshaft sensor gear can be the source of misfiring. If misfiring happens only at idle, the EGR valve and purge valve need to be checked, as either one could be stuck open.įaulty valve train components such as worn camshaft lobes, collapsed lifters, bad rocker arms or stretched timing chain can also cause the engine to misfire. Valve adjustment may need to be checked, as valves that are out of adjustment can cause misfiring at a cold start, which is, for example, a common issue in some older Honda engines. A low coolant level and white smoke can also point to a leaking head gasket. Pressure-testing the cooling system might help identify a leaking head gasket that can also cause misfiring. Read more about STFT and LTFT fuel trims here. Often a bad mass air flow sensor causes the engine to run lean causing random misfire. The short term fuel trim (STFT) and long term fuel trim (LTFT) need to be checked with a scan tool to see if the air/fuel mixture is not too lean. Read more: Vacuum leaks: common sources, symptoms, repairs. The engine might need to be checked for vacuum leaks. Basics such as compression, timing and fuel pressure will also need to be checked if no obvious fault is found. If you don't have access to the factory repair manual, Google 'Make Model Year service bulletin code P0301'. An important step is to check for related service bulletins issued by the car manufacturer. Signs of arcing on the ignition coil also point to the faulty part. The same procedure can be used to identify a bad fuel injector. ![]() For example, mechanics can identify a faulty on-plug ignition coil by swapping the coils between the cylinders and checking if the misfire moved with the coil or stayed at the same cylinder. The cause of misfire of one of the cylinders should be fairly easy to pinpoint if the problem is present at the time of checking. Read more: Catalytic Converter: problems, replacement options. Problems with the crankshaft position sensor (CKP) or camshaft position sensor (CMP) Stuck-open EGR valve or purge valve (solenoid) If the code P0300 occurs with other codes, such as, for example, P0171, P0101, P0102, P0420, P0401, the additional codes must be diagnosed first, as the random cylinder misfire often happens as a result of other problems. What can cause the code P0300 - Random cylinder misfire: Problems with the valvetrain components Low compression in the affected cylinder Examples of vacuum leaks include: leaking intake manifold gasket, broken PCV valve or PCV hose, disconnected vacuum line, cracked vacuum line A vacuum leak will cause misfire in the cylinder closest to the source of the leak. Carbon build up on valves and injectors (common in engines with Direct Injection) Damaged ignition coil primary circuit wires (often chewed by critters). Worn-out, cracked or fouled (in the photo) spark plugs. Steps to diagnoseįouled spark plug Carbon buildup on an intake valve Signs of automatic transmission problems.How to check the engine when buying a used car.How to get the best deal on a used car?.Buying a Used Car: 10 Common Mistakes to Avoid.Refer to the PC/ED manual for normal diagnostics. No: Replace only the spark plug(s) from the cylinders(s) associated with the P035X DTCs and do not continue with this bulletin. Does the ignition coil-on-plug(s) inspected show signs of damage? Refer to the above images for examples of damage. Inspect the ignition coil-on-plug(s) that have been removed for cracks and/or signs of heat-related damage. Remove only the spark plug(s) and ignition coil-on-plug(s) from the affected cylinder(s).ģ. Refer to the Powertrain Control/Emissions Diagnosis (PC/ED) manual for normal diagnostics.Ģ. Using the IDS scan tool, retrieve continuous memory DTCs. Some 2006 Zephyr 2006-2008 Fusion and Milan 2007-2008 MKZ, Edge and MKX and 2008 Taurus, Taurus X and Sable vehicles built on or before Maand equipped with a 3.0L or 3.5L engine may exhibit a malfunction indicator lamp (MIL) on with diagnostic trouble codes P0351, P0352, P0353, P0354, P0355 and/or P0356 present in the Powertrain Control Module (PCM) and with one or more damaged ignition coil-on-plug(s).ġ. Note: This article supersedes TSB 13-4-17 to update the Service Procedure and Part List.
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