a) Poor ignition caused by the ignition system (such as damaged spark plugs, high-voltage wires, distributor covers, distributor heads, ignition coils, or primary ignition issues that only affect a single cylinder or a pair of cylinders). Usually, an ignition oscilloscope can be used to identify these issues or troubleshoot them;
b) The ignition failure caused by the rich mixture sent to the cylinder (various possible reasons) has a dangerous air-fuel ratio of approximately 13:1 for a given dangerous mixture;
c) The ignition failure caused by the lean mixture sent to the cylinder (various possible reasons) has a dangerous air-fuel ratio of 17:1 for the given dangerous mixture;
d) The poor ignition caused by cylinder pressure is caused by mechanical problems, which reduce the pressure of the fuel air mixture before ignition and cannot generate enough heat, which hinders combustion and increases the oxygen content in the exhaust. (For example, valve burning, piston ring breakage or wear, cam wear, valve jamming, etc.);
e) The defect caused by vacuum leakage in one or several cylinders can be determined by adding propane to the suspected vacuum leakage area (intake impeller, intake manifold gasket, vacuum pipe, etc.), and observing the waveform of the oscilloscope when the signal increases and the peak disappears due to the addition of propane. When the vacuum leakage related to one or several cylinders causes the mixture entering the cylinder to exceed 17:1, The ignition failure caused by vacuum leakage occurs.
f) The ignition failure caused by imbalanced injection of fuel injectors is only found in multi-point injection engines. The ignition failure caused by a rich or thin mixture of fuel in a cylinder is due to the actual amount of fuel injected by each nozzle during injection, which is too much or too little (nozzle blockage or jamming). When the air-fuel ratio of the mixture in a cylinder or several gasoline exceeds a dangerous level at 17:1, a lean ignition failure occurs, while a lean ignition failure occurs below 13:1, resulting in an imbalanced injection of fuel into the fuel injector and resulting in poor ignition. Usually, the possibility of poor ignition caused by the ignition system, poor cylinder pressure ignition, and individual cylinder vacuum leakage can be excluded for judgment. Fuel injection imbalance. A car oscilloscope can be used to rule out ignition defects caused by the self ignition system and cylinder pressure (such as ignition defects caused by the ignition system and power balance cylinder pressure issues). To eliminate vacuum leaks related to individual cylinders, the usual method is to add propane (intake manifold, carburetor pad, etc.) to the area or surroundings where vacuum leaks may occur. At the same time, as previously mentioned, the method of observing the waveform of the oxygen sensor signal from an oscilloscope is used to achieve the goal. Usually, in multi-point fuel injection engines, if it cannot be confirmed that ignition defects are caused by types a, b, and c, the possibility of severe noise in the oxygen sensor waveform caused by imbalance can be determined. If there are obvious clutter on the signal of the oxygen sensor, which is abnormal for the type of system being judged, it will usually be accompanied by repeated and testable engine failures at idle (such as detonation of each cylinder ignition). Usually, if the clutter is obvious, the engine failure will ultimately be related to various spikes on the waveform. Clutters that are not accompanied by obvious engine failures are not easily eliminated (which is correct in some cases). That is to say, when individual spikes that generate clutter on the waveform are ultimately unrelated to the engine failure, the possibility of excluding them in repair is very small. In summary, the rule for judging clutter is: if it can be concluded that there is no vacuum leakage in the intake manifold, the content of hydrocarbons (HC) and oxygen in the exhaust is normal, and the engine's rotation or idle speed is relatively balanced, then clutter may be acceptable or normal.