The new engine is "powerless" and vibrates at 80 km/h. What's wrong?
2026/03/27
Fault Phenomenon
The vehicle idles perfectly normally, but obvious shaking occurs once the speed reaches 80 km/h during acceleration. When the accelerator pedal is floored abruptly during hard acceleration, the vehicle suffers severe jerking. The engine malfunction indicator lamp illuminates, and the instrument panel prompts reduced engine power with no response when stepping on the accelerator.
Fault Diagnosis
The trouble code clearly points to fuel pressure issues, and the complete engine mechanical assembly has already been replaced, ruling out any mechanical faults.
Connect a diagnostic scanner for a road test and retrieve freeze-frame data. According to the test readings, the actual high fuel pressure closely matches the target pressure when the engine runs smoothly after startup. However, the actual fuel pressure drops sharply as soon as engine RPM rises abruptly.
We conduct a detailed analysis of the abnormal data captured at this moment. The readings from the low-pressure fuel pressure sensor, which monitors the low-pressure fuel line, meet the ECM operating requirements, confirming the low-pressure fuel pump functions normally.
At the time of the high-pressure fuel rail pressure sensor malfunction, the measured pressure is only 0.1 MPa, far below the target pressure. We preliminarily suspect a fault within the high-pressure fuel supply system.
The high-pressure fuel pump delivers normal fuel supply at low engine speed, which makes pump internal failure less likely. When engine speed rises, fuel rail pressure drops sharply instead. This may be caused by insufficient fuel supply from the low-pressure line to the high-pressure pump; after fuel consumption, the pressure inside the fuel rail falls. Therefore, we inspected the pipeline connecting the low-pressure fuel pump to the high-pressure fuel pump.
A detailed analysis of the abnormal data recorded at the fault moment was carried out. Readings fed back by the low-pressure fuel pressure sensor for the low-pressure fuel line meet the operating requirements of the ECM, confirming the low-pressure fuel pump works properly. At the moment of the high-pressure fuel rail pressure sensor fault, the measured pressure is only 0.1 MPa, far below the target pressure. We preliminarily suspect a malfunction in the high-pressure fuel supply system.
After removing the fuel supply hose connected to the high-pressure fuel pump, we blew air through the hose by mouth for inspection. Air flows through smoothly from one end, while air can pass through the other end but with heavy resistance.
The technician suspected the hose was installed backwards. After cross-comparison with a fault-free vehicle, this suspicion was confirmed. The root cause of the malfunction was fully identified.
Troubleshooting
Reinstall the fuel hose correctly, and the fault is eliminated.
