Why does the Nissan Sylphy not start? A repair case study

[DiAva]

Nissan Sylphy not starting is generally caused by lack of fuel, battery depletion, or no power. Repair case study: After parking for one hour, the vehicle failed to start, and a slight abnormal noise was heard from inside the engine during startup. Inspection: The battery voltage was normal, the starting system was normal, the engine was running normally, and the fuel pressure was normal. Using the CONSULT-III vehicle diagnostic tool, no fault codes were stored. The spark plugs were removed, and the sparking condition of each cylinder was checked. It was found that cylinders 1, 2, and 3 were not sparking, while cylinder 4 was sparking normally. Fault determination: Cylinders 1, 2, and 3 had no high-voltage ignition, causing the engine to fail to start normally. The ignition coils and ignition wiring were checked and found to be normal. After replacing the spark plugs, the fault remained unchanged. The engine control unit (ECU) was checked, and the ignition output signals for each cylinder were examined. It was found that cylinders 1, 2, and 3 had no ignition signal, while cylinder 4 had a normal ignition signal. After replacing the ECU, the fault still persisted. Fault analysis: The timing signal from the engine to the ECU was incorrect, causing the ECU to fail to calculate the correct ignition timing. There was no ignition signal output for cylinders 1, 2, and 3. The ECU outputs the ignition sequence for each cylinder based on the crankshaft position sensor and related wiring, which were all normal. The timing phase waveform diagrams of the crankshaft and camshaft were read, and an abnormality was found, showing a significant difference from the waveform diagrams of a normal vehicle. It was inferred that there was an internal mechanical fault in the engine, possibly due to damage to the sensor signal disk or timing misalignment, leading to incorrect timing phase signal output. The crankshaft position sensor and camshaft position sensor were removed and checked, and the signals were normal. After removing the valve cover and positioning the piston of cylinder 1 at top dead center, it was found that the phase of the intake camshaft and exhaust camshaft was incorrect. The engine was disassembled for inspection, and it was found that the connection between the intake camshaft and the camshaft sprocket was damaged. After replacing the damaged parts and reassembling the vehicle, the fault was resolved.