Car Jerks and Loses Power While Driving – Case Study: Mercedes-Benz CLA with M270 Engine
Car jerks and loses power while driving; this is a warning sign you should never ignore. It’s not just annoying; it can signal a deeper mechanical issue that could leave you stranded or damage your engine.
In this real-world case of a Mercedes-Benz CLA equipped with the M270 engine, a seemingly minor jerking issue turned out to be a failing high-pressure fuel pump. Here’s how expert diagnostics pinpointed the problem and brought this car back to smooth performance.
Customer Complaint: Car Jerks and Loses Power While Driving
A customer brought their Mercedes-Benz CLA 180 to the workshop, reporting that the car jerks and loses power while driving, especially during acceleration. The vehicle would hesitate, stumble, and then lose significant power, making it difficult to drive smoothly.
Initial Inspection and Diagnostic Steps
To diagnose why the car jerks and loses power while driving, the technician followed these steps:
- Road Test
During the test drive, the issue was confirmed : the car experienced intermittent jerking and a noticeable lack of power, particularly under load. - Quick Test with Diagnostic Scanner
A full system scan revealed no stored fault codes related to the drivetrain, which suggested the issue might be occurring in real-time, without triggering fault memory. - Live Data Analysis
The technician checked fuel pressure values while driving. The readings showed abnormally low high-pressure fuel delivery during acceleration, indicating a fault in the high-pressure fuel pump (HPFP) system.
Root Cause: Faulty High-Pressure Fuel Pump
The M270 uses a direct injection system, which requires consistent and strong high-pressure fuel delivery. In this case, the high-pressure fuel pump was failing intermittently, especially under load, causing fuel starvation and power loss.
Symptoms of a failing HPFP include:
- Engine jerking under acceleration
- Poor throttle response
- Engine stalling or surging
- No fault codes, but abnormal live fuel pressure readings
Repair Process
- Fuel System Inspection
Before replacing the HPFP, the technician:- Checked the low-pressure pump (in-tank) : operating correctly
- Verified fuel filter | clean and unobstructed
- Inspected fuel lines and connectors : no leaks or restrictions
- HPFP Replacement
The faulty high-pressure fuel pump was replaced with a new OEM unit. - System Reset and Adaptation
After installation:- Performed fuel system bleeding
- Reset fuel pressure adaptation values
- Verified proper function via test drive and live data
Final Results
After replacing the faulty high-pressure fuel pump, the Mercedes-Benz CLA 180 regained:
- Smooth and responsive acceleration
- No jerking or hesitation
- Normal fuel pressure during all driving conditions
This confirmed that the root cause of the car jerking and losing power while driving was indeed the failing HPFP.
Expert Advice: Don’t Ignore the Early Signs
If your car jerks and loses power while driving, it could be due to:
- Fuel delivery problems (HPFP, low-pressure pump, clogged filter)
- Ignition issues (spark plugs, coils)
- Sensor failures (MAF, MAP, throttle position)
- Transmission or drivetrain faults
Timely diagnostics using advanced tools and real-world testing is essential. Delaying the repair can worsen fuel system damage and increase repair costs.
Conclusion
This case study highlights the importance of fuel system health in modern gazoline engines like the M270. A failing HPFP can manifest as jerking and power loss, but with proper diagnostics and repairs, your vehicle’s performance can be fully restored.
If your car jerks and loses power while driving, don’t wait get it inspected by a qualified technician to prevent more serious engine or fuel system damage.
What are the symptoms of a failing high-pressure fuel pump?
A failing high-pressure fuel pump (HPFP) can lead to a range of performance issues, especially in vehicles with direct injection systems like the M270 engine in the CLA 180.
One of the most noticeable symptoms is when the car jerks and loses power while driving, particularly during acceleration or uphill driving. You may also experience difficulty starting the engine, rough idling, poor throttle response, or even stalling at low speeds.
In many cases, the vehicle may not trigger a fault code, making it harder to diagnose without live fuel pressure monitoring. Another common sign is inconsistent engine performance under load or during overtaking maneuvers.
If your car hesitates, feels sluggish, or surges unpredictably, the HPFP could be to blame. Addressing this issue early can prevent further damage to injectors and the fuel system, ensuring smoother and safer driving.
Is it safe to drive if my car jerks while accelerating?
Driving a vehicle that jerks and loses power while accelerating is not safe and should be addressed immediately.
Jerking under load often indicates an underlying issue with the engine, fuel system, or transmission, and continuing to drive could worsen the problem or lead to sudden power loss—potentially dangerous on highways or in heavy traffic.
In the case of the Mercedes CLA 180, a failing high-pressure fuel pump caused inconsistent fuel delivery, making the car unstable during acceleration. This kind of fault can compromise overtaking, merging, and even maintaining speed on inclines.
Additionally, unresolved jerking can damage other components like the turbocharger, injectors, or catalytic converter due to improper combustion. If your vehicle begins to hesitate, stumble, or lose power unexpectedly, it’s best to stop driving and have it inspected by a qualified technician as soon as possible to avoid a breakdown or accident.
