Mercedes-Benz CLA, 2013, Vantaa

The car has only been test-driven and performed well based on these observations, but starting took longer than normal.

Copy of the diagnosis carried out by the mechanic:

Very difficult to start. Cranking time as long as 10 seconds before starting unevenly.

Could there possibly be an injector fault?

Driven into the workshop, running roughly.

Quick test performed and attached.

No fault codes are stored in the engine control unit.

The injectors' return line was disconnected and the engine started; fuel flowed evenly from all of them, with no differences.

The injector quantity correction values indicate a fault with injector 3 (cylinder 3); the correction value is high.

Injectors removed. No fuel residue on the tips; all were essentially equally wet.

The injectors were connected to the fuel rails in an upright position and the fuel sprays checked. All four injectors spray fuel properly, and none of the injectors drips.

The injectors are not original to the car. They have apparently been replaced with refurbished injectors, as the part numbers have been removed from the injectors and the correction code does not match the label on the valve cover, which shows the correction codes for the original injectors.

Injectors refitted.

Next, the glow plugs were removed and compression pressures measured.

In the first measurement, the compression pressure in none of the cylinders exceeded the minimum (17 bar).

In the second measurement, the pressures increased but showed very clear differences:

Cylinder 1: 16 bar

Cylinder 2: 20 bar

Cylinder 3: 19.5 bar

Cylinder 4: 18 bar

This therefore appears to be an engine fault.

Leak-down was measured next. The measurement results were unclear; the piston does not remain properly at top dead centre during the compression stroke. Leakage of 60–30% was detected in every cylinder.

Could the engine damage have occurred with the previous injectors, when liquid compression formed in the cylinder due to leaking injectors and consequently damaged the engine?

For this reason, starting—especially when the engine is cold—takes longer because there is insufficient compression.

Serious engine damage is strongly suspected.