Ignition and combustion problems are unique to spark ignition engines (commonly referred to as "gasoline"), as diesel engines are self-igniting and do not require spark ignition. When diagnosing ignition or combustion problems, it is helpful to identify whether they are intermittent or constant to aid the workshop in diagnosing. Possible causes of ignition misfires / misfires can be damage to the ignition system or the injection nozzles, or there can be loss of compression in the engine.
Ignition misfires / combustion misfires
First of all, it should be determined which cylinder is affected by the misfiring / misfiring. This can be done, for example, by reading out the fault memory or by carrying out a compression test. Also, the ignition wires or ignition coils can be swapped between cylinders to see if the fault is spreading. Unlike diesel engines, gasoline engines require spark ignition, which is used for the spark plugs. In the event of a faulty ignition system, various factors can play a role:
|Spark plug wear or failure||ignition coil failure|
|Ignition wire damage or failure||Problems with the ignition distributor|
|Ignition module malfunction||Malfunctions in the ignition system|
|Corroded or loose electrical connections||Ignition timing problems|
|Fuel quality or composition||Problems with the ignition system electronics|
|Mechanical problems in the engine
(e.g. valve or piston problems)
Loss of compression in the engine
If one or more cylinders cannot hold the pressure, it is called a loss of compression. This happens when pressure is released from the combustion chamber during the compression of the fuel-air mixture (the "2nd stroke"), which can cause ignition or combustion problems. In the workshop, a compression test can show which cylinder has lost compression. This involves removing a spark plug and inserting a compression tester into the engine in its place. When the engine is then started, the pressure generated is measured and compared with the target values or the measurement results of the other cylinders.
Instructions for measuring compression:
|1||Preparing the engine: switch off the vehicle and allow the engine to cool down.|
|2||Remove spark plugs: Remove all spark plugs.|
|3||Connect the compression gauge: Screw the compression gauge into the cylinder instead of a spark plug.|
|4||Fully Depress Accelerator Pedal: Fully depress the accelerator pedal to keep the engine idling during the test.|
|5||Start the engine and rev it several times: Start the engine with the starter and rev it several times to build up the compression pressure.|
|6||Carry out the measurement: Read off the compression value and note it down. Repeat this for all cylinders.|
|7||Compare Results: Compare the determined compression values and make sure they are within the acceptable range.|
|8||Reinstall spark plugs: Reinstall all spark plugs in their respective cylinders.|
|9||Test Engine: Start the engine and look for any performance problems or abnormalities that could indicate low compression.|
Possible causes of a loss of compression!
|Defective or leaking piston rings||Problems with the piston rings that can cause a leak in the compression chamber.|
|Problems with the valves or the valve guide||Damage to the valves or valve guides that can cause pressure loss during compression.|
|Damage to the camshaft or crankshaft||Damage to the camshaft or crankshaft that could result in loss of compression.|
|Errors during assembly after previous repairs||Incorrect assembly or reassembly after previous repairs that may result in leaks.|
|Cracks in the cylinder head gasket, the cylinder head or the cylinder wall||Cracks in major components such as the head gasket, cylinder head, or cylinder wall that can prevent proper compression.|
|Mechanical wear on the engine||General wear and tear of the engine, which can lead to a loss of compression.|
The cost of fixing a loss of compression can vary widely depending on the specific cause and engine type. In some cases, a significant loss of compression can even result in a economic total loss of the vehicle.
Defective injectors / injectors
In order to ensure smooth operation of all cylinders, the amount of fuel determined by the engine control unit to be ideal must be injected correctly. Under certain circumstances, however, defective injection nozzles can lead to over- or under-injection of fuel in the cylinder, which in turn can cause ignition or combustion problems (misfiring / misfiring). Other possible reasons can be: A broken cable or an electronic defect, a defective engine control unit, a defective intake manifold switchover, a defective air mass meter or a defective camshaft adjuster.