Fault diagnosis
Maintenance personnel test drive found that the car idles normally, but the road test acceleration break-in phenomenon is very obvious.
- Test engine control unit, fault code display for 4 cylinder misfire. Will 4 cylinder injector and 1 cylinder of the alignment, the fault remains.
- Check the control harness of the injector and the hitch of the engine control unit, there is no abnormality. Connect the cleaning equipment, run the engine, add new fuel; interchange spark plugs and ignition coils, the fault remains.
- The three-way catalytic converter was inspected with a borescope and no clogging was found. The 3-way catalytic converter was still replaced to dispel any doubts about clogging, but the situation remained unchanged.
- Check the air intake of the engine, no air leaks.
- Checked the variable intake, no sticking of the flap, and normal motion check. Rotate the intake camshaft and visually inspect the valve opening without abnormality.
- Replace the eccentric shaft position sensor, crankshaft position sensor, and camshaft position sensor; replace the eccentric shaft servo motor, the fault remains.
- With a normal car to swap the engine control unit and anti-theft control unit, the fault remains.
- Disconnecting the plug of the eccentric shaft servo motor, the fault phenomenon disappeared.
The analysis suggests that after disconnecting the servomotor, the engine’s output torque shifted to the throttle control mode. Thus, it seems that the fault should be related to the control of the intake valve.
The intake manifold was removed and visual inspection revealed signs of air leakage at the 4-cylinder intake valves. This should be where gas from the work stroke is spilling out due to poor valve closure. Remove the valve cover to check the intake camshaft and valve return springs, no obvious abnormalities, and in normal vehicles swap the intake camshaft and eccentric shaft, the fault is still the same. This shows that the problem should be in the valve.
Troubleshooting
Replace the cylinder head assembly with valves and test drive to confirm the troubleshooting.
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