How to Diagnose Engine Failure

by MOU YONG HONG on December 01, 2021

The automobile EFI engine can't start, and there is no sign of the car. What's the matter? Below VEP Engine Parts introduces the failure phenomenon, reason, and troubleshooting of the EFI engine.

The engine can not start failure phenomenon

When the starter is intact and has both oil and electricity when the engine is started, the starter can drive the engine to run, but there is no sign of starting. Failure to start anyhow is called failure to start.

Causes of engine failure to start

The common reasons for the failure of the engine not starting (no initial combustion) are: The ignition system does not ignite and the ignition timing is inaccurate; the injector does not work, the cold start injector does not inject, the injection pressure is too low, the injector is blocked or leaks, the injection control signal is poor, and the fuel pump does not work, Air intake system leaks, cylinder pressure is too low, etc. The fuse is blown; the fuel does not enter the cylinder; there is no high-pressure fire (such as the ignition coil is damaged); the gasoline pump is not working properly or is seriously blocked, or the one-way valve is not closed tightly, the gasoline pump circuit is short-circuited or open; the gasoline pump relay or main electrical appliance is faulty (Such as contact ablation); three-way catalytic converter is blocked; fuel pressure is low; fuel injectors work poorly, etc.

Mechanical reasons: insufficient compression force, too loose or broken timing belt, and tooth skipping failure.
Electronic control reasons: the distributor is faulty, such as the signal line is broken, the Hall sensor triggers the impeller positioning head to break; the pulse ring at the front of the camshaft of the synchronous pulse signal generator falls off and the positioning end is damaged; the electronic ignition controller is faulty (no points Electric vehicles); the pressure sensor is faulty (such as internal short circuit); the injector does not get the pulse signal of the switch (the ECU is not grounded); the fuel pressure regulator is faulty (the internal diaphragm is broken); the crankshaft position sensor is faulty, For example, the signal cannot be generated due to dirt; the signal generator of the crankshaft position sensor is poor or the rotor is toothed; the ECU is faulty, such as poor grounding, ground wire open, internal short circuit, circuit breakdown, etc.; assembly errors, such as oil pressure adjustment The oil inlet pipe of the engine is connected to the oil return pipe, the two crankshaft position sensor plug-ins are inserted reversely (some cars have two crankshaft position sensors), and the camshaft position sensor triggers the impeller to be reversed.

Diagnostic and troubleshooting of engine failure

The specific procedures for the inspection and elimination of the failure of the EFI engine to start are: self-diagnose the engine failure and check for failure codes, such as the crankshaft position sensor failure. If there is a fault code, you can find the fault location according to the displayed fault code.

(1) Method of reading fault code:
Set the ignition switch to "ON", but do not start the engine; use a jumper wire to bridge the jacks "TE1" and "E1" on the diagnostic socket. As shown in Figure 4-6. The “CHECK ENGINE” fault indicator on the dashboard shown in Figure 4-7 will flash, and the fault codes will be displayed in the order of the faults.
Remove the diagnostic jumper after completing the inspection. The fault code recorded in the ECU must be cleared after repairing the faulty part. The cleaning method is: turn off the ignition switch and remove the EFI fuse from the fuse box for more than 10 seconds.

(2) Check the fuse box:
The key point is whether the fuses such as EFI and IGN in Figure 4-9 are blown. When starting, smell the exhaust gas from the exhaust pipe. If there is no gasoline smell, the fuel supply system is more likely to malfunction; if there is a strong gasoline smell, the ignition system is more likely to malfunction.

(3) High-pressure test:
Unplug the high-voltage bus line from the distributor or the high-voltage branch line from the cylinder block, make the wire end metal 5~6mm away from the cylinder block, start the engine, and observe whether there is a strong blue high-voltage spark at the high-voltage line end. If there is no high-pressure spark or the high-pressure spark is very weak, the ignition system is faulty.

(4) Inspection of ignition system:
Turn on the ignition switch and check the low-voltage circuit of the coil. There should be a normal 12V voltage from the ignition coil (+) end to the ground, and the igniter +B end voltage should be 12V, otherwise check the power supply circuit; the igniter C(1) end should There is a voltage close to 12V, otherwise, the ignition coil should be checked. When the starter drives the engine to run, use an oscilloscope to detect that the igniter IGT and IGF terminals should have square wave pulses as shown in Figure 4-10, and the crankshaft position sensor output terminals NE, G1, G2 to G(1) should have signal generation.
If there is no signal from the crankshaft position sensor, the sensor should be repaired. If the crankshaft position sensor has a signal but the IGT has no signal, then the ECU is faulty; if there is a signal at the IGT but no signal at the IGF, the igniter is faulty.

(5) Check the ignition timing:
If the ignition timing is too far apart, the engine will show no signs of starting. The method to check the ignition timing is: connect the timing lamp to the engine (clamp the timing lamp wire clamp on the high-voltage line of the first cylinder); run the engine at idle speed; use a jumper to connect the terminals TE1 and E2 on the diagnostic socket; As shown in Figure 4-12, use the timing lamp to check the ignition timing, which should be 10° before top dead center; disconnect the jumper wire on the diagnostic socket, and use the timing lamp to further check the ignition timing. The timing mark is at 10 °The amount of movement on each side shall not exceed 5°. If the ignition timing is not correct, check and adjust. The method is: some models have an adjusting screw on the distributor, which can be loosened, and the ignition timing can be changed by rotating the distributor left and right. Otherwise, the assembly relationship between the camshaft and the crankshaft should be checked, such as whether the timing belt is assembled correctly.

(6) Inspection of oil circuit:
If the fuel supply system is faulty, causing the fuel pressure to be too low, it will also make the engine unable to start. Short-circuit the +B of the detection jack and FP, turn on the ignition switch, you should be able to hear the sound of the fuel pump at this time, and when you hold the fuel inlet pipe with your hand, you should feel the oil pressure pulsation of the fuel inlet pipe. The pump is malfunctioning; if possible, connect a gasoline pressure gauge to the idle nozzle or a convenient place to measure the gasoline pressure. The normal fuel pressure should be about 0.3MPa when the engine is not running. If the fuel pressure is too low, wrap a soft cloth with pliers and clamp the oil return pipe of the oil pressure regulator to block the oil return path. At this time, the oil pressure should rise rapidly. If the fuel pressure rises slowly or hardly, it means The oil circuit is blocked or the electric fuel pump is faulty.

If the oil pump is normal and the oil pressure is low, the oil pressure regulator is faulty. If the petrol pump is not working, check the control circuit of the petrol pump. If the circuit is normal, the petrol pump is faulty.

(7) Inspection of fuel injector:
Use an oscilloscope to detect whether there are electrical pulses at both ends of each injector's wiring. If not, check the control circuit part; if so, remove each injector, add 12V voltage to the injector terminal, and use a spray such as derusting water or carburetor cleaning agent from the inlet of the injector Spray spray at the end to see if there is spray from the nozzle. If not, it means that the nozzle is blocked and should be cleaned or replaced. If possible, the fuel injector can be cleaned and inspected with testing equipment.

(8) Check the cylinder compression pressure:
If the above checks are normal, the compression pressure of the engine cylinder should be further checked. If the cylinder compression pressure is lower than 0.8MPa, it means that the engine mechanical part is faulty.


Please note, comments must be approved before they are published