What are the possible causes of engine intake pipe backfire?

① Air leakage in the air intake system. The air hose is damaged or the hose connector is loose, the exhaust gas recirculation valve cannot be closed, and the oil filter cover is not closed correctly. ② The ignition time is too early. (3) The fuel injector does not inject fuel during cold start (tempering during cold start). Poor contact of temperature time switch, failure of cold start injector, and poor connection between temperature time switch and cold start injector line. ④ The injection pressure is low. The oil circuit is leaking, the fuel filter and the oil circuit are blocked, the fuel pump is not easy to use, and the fuel pressure regulator is not easy to use. ⑤ The injector is not working properly. The injector nozzle is blocked, the series resistance of the injector leaks, and the power cord or connector of the injector is in poor contact. ⑥ The fuel injector control signal is bad. Bad air flow sensor, bad water temperature and air temperature sensor, bad throttle position sensor and bad wiring from sensor to ECU. ⑦ The battery voltage is too low. Battery damage, charging system failure.