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Troubleshooting of Starting Difficulty of Diesel Engine

Feb. 16, 2019

The difficulty of engine starting is that the starter can drive the engine to turn at normal speed and has obvious signs of running, but it can't start, or it needs to start repeatedly or for a long time before the engine can start. For the trouble of starting, it is necessary to distinguish between the cold car and the hot car, or whether the cold car or the hot car appears. The cause of this failure is usually in the fuel injection system.

Troubleshooting of Starting Difficulty of Diesel Engine.jpg


1. Fault Phenomenon


The crankshaft rotation speed is normal when starting, but it takes a long time to start, or there are obvious signs that the crankshaft can't start.


2. Failure Cause


Air leakage in intake system; low fuel pressure; clogging of air filter; fault of water temperature sensor; malfunction of air Flowmeter; failure of idle speed control valve or additional air valve; failure of cold start injector; leak of injector; Incorrect ignition timing; starting switch to computer connection broken; cylinder compression pressure is too low.


3. Fault Diagnosis and Troubleshooting


A. Perform fault self-diagnosis. If there is a fault code, by the fault code to find the corresponding cause of failure.


B. Check the vacuum of the inlet during idling. If the vacuum degree is less than 667 kPa, the air leakage in the intake system should be checked at the joints, gaskets, vacuum hoses, exhaust gas recirculation system and fuel evaporation recovery system.


C. Check the air filter. If there is a filter plug, it should be cleaned or replaced.


D. If the engine can start normally when the throttle is about 1 / 4 open, and if the throttle is difficult to start when the throttle is completely closed, the idle speed control valve and the additional air valve should be checked to see if the idle speed control valve and the additional air valve are working properly. In cold car idling operation, unplug idle control valve harness or clamp the additional air valve hose with pliers during idle running. If engine speed does not decrease, idle speed control valve does not work properly. Idle speed control valve and its control circuit should be checked.


E. Check fuel pressure. Use a wire to short the two test sockets of the electric gasoline pump, then turn on the ignition switch to make the electric gasoline pump run. In this condition, the fuel pressure should be about 300 kPa. If the pressure is too low, check the oil pressure regulator for oil leakage, gasoline filter plug, gasoline pump maximum pump oil pressure is normal.


F. Check water temperature sensor or air Flowmeter. Unplug the water temperature sensor or air Flowmeter wire harness and measure the resistance between the water temperature sensor and the air Flowmeter terminal using a multimeter. If the resistance value does not meet the standard, it should be replaced.


G. If it is difficult to start in a cold car and start normally in a hot car, check that the injector works properly. Check whether there is a voltage of about 12 V at the plug of the wire harness of the cold starting injector. If there is no voltage, the control circuit is faulty, the cold start temperature-time switch and its control circuit should be checked. If there is a voltage at the wire harness plug during starting, check that the electromagnetic coil resistance of the cold start injector is normal and that the nozzle hole is blocked.


H. If it is not easy to start in the hot car, check that the fuel system pressure is normal after the ignition switch is off. The fuel pressure should be measured by the oil pressure meter. After turning off the ignition switch (extinguishing), the fuel pressure should be kept not less than 150 kPa within 5 min. If the pressure is too low, check for oil pressure regulators, electric gasoline pumps, injectors, etc.


I. Check ignition timing during idle run. If it does not meet the standard value, it should be adjusted


J. Check that the starting signal from the start switch to the computer is normal. If the starting signal of the starting switch is not received by the computer, the starting thickening control can not be carried out, which will lead to the difficulty of starting. To this end, check from the computer wire harness plug to start whether there is a starting switch signal to the computer. If there is no signal, check the starting switch and circuit.


K. Check cylinder compression pressure. If the pressure is too low, the engine should be removed and checked.


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