Why the Engine is Hard to Start
Difficulty in starting the engine means that the starter motor can drive the engine to rotate at a normal speed, and there are obvious signs of starting, but it is difficult to start; or it needs to be started several times in a row, or the starter motor is turned for a long time before the engine can be started.
- Case Analysis
Failure phenomenon: a car is difficult to start cold, and it can start normally when it is started immediately after a short pause after warming up, but it is still difficult to start again after waiting for 15min.
Failure Analysis: The possible causes of initial starting difficulties are as follows:
l Excessive carbon deposits in the cylinder combustion chamber, most of the fuel is adsorbed by the carbon deposits during the initial startup every day, after the initial startup the carbon deposits are in a saturated state, and then every time during the day, the vehicle can start normally.
l Fuel pressure is too low, it is necessary to establish normal pressure in the fuel line first, there is no residual pressure, the engine must be started 2 times in a row to complete the start. As a result, not only is it difficult to start the engine when it is warmed up, but it is also difficult to start it again after waiting 15min after turning off the engine.
Troubleshooting: When testing the residual pressure, connect the fuel pressure gauge, start the engine to establish a normal fuel pressure under the premise, turn off the engine, close the fuel pressure tester shut-off valve, and then open it after 10min, the residual pressure should not be less than 200kPa.
If the residual pressure is too low, there are three main reasons:
- Poor sealing of the fuel pump outlet check valve;
- Poor sealing of the fuel pressure regulator;
- Poor sealing of the injector.
Based on the principle of first simple and then complex, carry out the inspection in the following order.
① Check the sealing of the fuel pump discharge check valve first. When the fuel residual pressure is lower than the standard value, it can be detected by the exclusion method. Close the shut-off valve on the fuel pressure gauge first, so that the fuel pump to the fuel pressure gauge is in a sealed state. Re-perform a residual pressure test, if this time the residual pressure is normal, it means that the fuel pump outlet check valve and the pipeline before the fuel pressure gauge sealing is bad.
② Check the sealing of the fuel pressure regulator. After closing the shut-off valve, the fuel pressure is still lower than the standard value, indicating that the fuel pump outlet check valve and the pipeline before the fuel pressure gauge are well sealed. Clamp the return pipe of the fuel pressure regulator with a clamping plate and carry out a residual pressure test again, if the residual pressure is normal this time, it means that the return valve of the fuel pressure regulator is damaged.
③ Check the sealing of the injector. After clamping the return pipe of the fuel pressure regulator with a clamping plate, the fuel pressure is still lower than the standard value, indicating that there is a leak in the injector. 30s fuel injection test, in 30s the injector leakage is not allowed to exceed one drop, otherwise it indicates that the injector sealing is bad. After checking the fuel pressure regulator diaphragm sealing bad.
Possible causes and countermeasures
1、The mixture is too thick
If it is difficult to start the hot engine, and will accelerate the pedal to the end (step on the end of the fuel injection) can be started normally, then the mixture is too thick. At this time, you can remove the air filter element, release a portion of the thick mixture accumulated in the air intake tract. In addition, after removing the filter element, the intake resistance becomes smaller, the smaller the intake resistance, the thinner the mixture, can start normally. Should focus on checking whether the charcoal canister solenoid valve is stuck in the open part.
2、Excessive carbon on the throttle system and bypass airway
Every day when you step on the accelerator pedal for the first time, you feel heavier than before, and it is difficult for the engine to start, but when you slightly step on the accelerator pedal, you can start normally, which means that there is too much carbon at the throttle, and the excessive carbon clogs up the throttle, resulting in difficulty in starting, and when you slightly step on the accelerator pedal, you can guarantee the intake of air so that it can be started normally, but when you are driving and relaxing the accelerator pedal, you will stall immediately. Should be timely cleaning throttle system and bypass airway, cleaning and re-matching, can be restored to normal.
3、Intake air temperature sensor disconnection or poor ground wire contact
There will be an abnormal low temperature signal, resulting in too thin a mixture, starting difficulties, but will not cause failure to start. Check the intake air temperature sensor, in addition to checking the resistance value at room temperature, but also to use the car's headlights after heating to check whether the resistance value is reduced. Usually disconnected negative temperature coefficient thermistor at room temperature resistance value is basically normal, but the resistance value does not change after heating.
4、cold weather battery posts poor contact
After a long time after the use of the battery pole head white crystalline particles, will make the battery leakage, cold weather parking after the engine can not start. Use boiling water to pour the crystallized particles on the head of the pole, can start normally. Maintenance with sandpaper to remove the white crystalline particles on the pole head, coated with grease, can be troubleshooting.
5、Bad grounding wire
Cold start difficulties, hot start normal, sharp acceleration when the engine speed drift, the most common fault is the engine ground line, transmission ground line, battery ground line or control unit ground line in at least one poor contact, re-tighten, the fault can be eliminated. If the engine control unit power supply or ground wire contact is poor, it will trigger its intermittent interruption, interruption of the control unit stops working, fuel and ignition control will be interrupted at the same time, that is, there is no oil and fire, so that the vehicle can not start.
After warming up the car will start normally, the reason is very simple, that is, thermal expansion and contraction. Engine start if a ground wire contact is poor, its temperature will be hot, hot expansion after the original gap eliminated, ground wire contact failure is temporarily gone.
6, too much carbon in the combustion chamber
Every day when you start for the first time, you need to start 2~3 times continuously (just start the fuel is absorbed by the carbon) before you can, and when it is serious, it will shake suddenly and violently, and even drive the body to shake together. Clean the carbon deposits in the combustion chamber, and drive at high speed for 20min after cleaning to solve the problem. After cleaning, turn off the engine directly, the second day may be due to the valve is cleaned after the residual sticky carbon adhesion, can not start.
7、Ignition coil short circuit
It will cause the engine starting difficulty, weak acceleration, black smoke from the exhaust pipe, while fuel consumption increases sharply. Replace the ignition coil to eliminate the problem.
8、the intake manifold absolute pressure sensor hose clogging or sensor and its circuit bad
① cold start normal, hot start difficulties, idling jitter, easy to stall, lack of power, accelerate the engine wheezing, fuel consumption increased significantly, black smoke from the exhaust pipe, which is typical of the intake manifold absolute pressure sensor vacuum hose blockage failure phenomenon. The control unit does not receive the air flow signal, enter the emergency protection program, the control unit will repeatedly adjust the idle stepper motor at idle, resulting in idle speed drift. Replace the clogged vacuum pipe to eliminate the problem.
② The intake manifold absolute pressure sensor or circuit is bad, which will cause the engine to idle erratically, idle incorrectly, start difficulties or start and then stall. When the above phenomena occur, the pressure sensor and circuit should be tested.
9、charcoal canister air filter clogging
The engine starts normally when it is cold, and it is difficult to restart within 15 minutes after the engine is turned off when it is hot, and it can start normally after a long time. When the engine is warmed up, there is a vacuum suction sound at the moment of opening the gas tank cover, but after opening the gas tank cover can start normally, indicating that the charcoal canister air filter clogging. Charcoal canister air filter clogging so that the tank's only air channel is closed, with the lowering of the oil level in the tank, the vacuum inside the tank to increase the bottom of the tank is sucked up, most of the gasoline collector filter inlet is blocked by the bottom of the tank, so that the amount of fuel into the reduction of the engine off within 15min to warm up within the need for 2 to 3 consecutive start-up can start the car. Replace the charcoal canister to solve the problem. The bottom of the fuel tank will be reset after a longer stay, and it can be started normally.
10、Excessive carbon deposits in the combustion chamber cause difficulty in starting for the first time every day.
The initial start-up needs to be started 3 times a day (the first 2 times the oil sprayed is absorbed by the carbon, and the carbon is saturated at the 3rd start-up), and then the start-up can be completed once a day, but the engine shakes when accelerating and closing the accelerator pedal during driving. This may be too much carbon in the combustion chamber, resulting in poor sealing of the intake valves, cleaning the combustion chamber can eliminate the problem. Too much carbon in the combustion chamber will also cause poor acceleration and maximum speed drop.
11、Carbon canister solenoid valve stuck in the open area
Charcoal canister solenoid valve stalled in the open position leads to starting difficulties, cold car at least 3 times to start to start the car, while the hot car start normal. Charcoal canister solenoid valve opening conditions is the engine coolant temperature above 75 ℃, the speed of 1500r/min or more, each time the opening time is not more than 90s, open the control unit according to the intake air temperature sensor signal to re-adjust the injection pulse width, in order to ensure the ideal air-fuel ratio.
When the charcoal canister solenoid valve is stuck in the open position, the control unit has no way of knowing about it, and it is impossible to re-adjust the injection pulse width for it, and the engine will only complete the initial start each day if it is started continuously in order to drive the over-concentrated mixture that has built up throughout the night out of the cylinders.
When warmed up, the mixture from the charcoal canister solenoid valve is limited due to the limited interval, so a normal start is basically guaranteed. If you start the accelerator pedal to the end, or remove the air filter element, stop for a moment to start normally.
12、EGR valve is stuck in the open position.
The EGR valve is stuck in the open position, resulting in starting difficulties (more than 3 times in a row before starting), unstable idle speed, acceleration shivering.
13、Input signal line of absolute pressure sensor of intake manifold is disconnected.
Intake manifold absolute pressure sensor input signal line disconnection will cause the start immediately after the stall. Intake pressure sensor input signal line voltage should be 5V, if the actual detection is 0, then the sensor is disconnected.
14、fuel pump and fuel filter failure
When the fuel pump and fuel filter failure caused by startup difficulties, the general fuel pump is able to work normally, the problem is mostly due to fuel pump screen clogging caused by the fuel pump can not be enough fuel suction, or fuel filter does not smooth fuel flow caused by insufficient fuel flow. Fuel pump screen clogging must be cleaned tank, and then replace the screen.
15、fuel injector clogging
Injector clogging, will make the fuel injection throttle and atomization is not good, resulting in cold start difficulties, need to start 2~3 times to start the car. Cleaning injectors can be restored to normal.
16、Coolant temperature sensor short-circuit, disconnection or poor ground wire contact
Coolant temperature sensor short circuit, will cause the mixture is too thin, the vehicle can not start; sensor disconnection or ground wire contact is poor, will cause the mixture is too thick, the cold car can start normally, hot car will appear to start difficulties, start the idle speed jitter, or even off. Check the ground wire, if the ground wire is normal, then further check the coolant temperature sensor.
