Checking Timing Retardation Due to Knock

CHECKING TIMING RETARDATION DUE TO KNOCK

Condition

- Diagnostic trouble codes (DTOs) in Motronic 4.4 absent.
- Diagnostic trouble codes (DTCs) in AW 50-42 absent.
- Engine at normal operating temperature.
- The fault is permanent.

Possible Source

- Timing retardation due to knock.





Checking Timing Retardation Due to Knock

- START engine.
- Go into scrolling values.
- Test drive the car on the road and watch parameter "KN.IGN.RET".
- If timing retardation due to knock constantly exceeds 10° while the car accelerates poorly or lacks power, it is probably because of this timing retardation.

Does ignition retardation constantly exceed 10°?

Yes:
- Proceed to test step below.

No:
- Proceed to Checking the Turbocharger Control Valve Control section.





Checking for Knock

Abnormal knock may be due to any one of the following reasons (which are not listed in any particular fault- tracing order).

Oil Carry-Over
- Combustion will be poor, resulting in knock, if the engine draws in oil through the crankcase ventilation system (possibly due to high oil level in engine).

Defective Spark Plugs or Ignition Cables
- May cause poor combustion, resulting in knock.

Defective Distributor Cap or Rotor
- May cause poor or faulty combustion, resulting in knock.

Loose or Defective Knock Sensor
- May provide the Engine Control Module (ECM) with faulty knock-related information.

Incorrect Fuel Grade
- May cause poor combustion, resulting in knock.

Extremely High Engine or Air Temperature
- May cause poor combustion, resulting in knock.

Incorrectly Adjusted Camshafts
- The intake and exhaust valve opening times will be incorrect if the camshafts are incorrectly adjusted.
- Ignition advance will also be incorrect as the distributor is mounted at the rear of the camshaft.
- This may cause poor or faulty combustion, and engine knock.

Mechanical Knock
- Mechanical knock may also be caused by worn mechanical components resulting in excessive bearing play, excessive piston clearance, valve rattle (faulty hydraulic tappets).

Was a fault detected?

Yes:
- Fault corrected.

No:
- Proceed to Checking the Turbocharger Control Valve Control section.