Poor Acceleration, Lack of Power

FAULT TRACING INFORMATION

Conditions
^ DTC's in Motronic 1.8 absent.
^ DTC's in AW 30-43 absent.
^ Engine warm.
^ Fault permanent.

Fault Sources
^ Ignition retardation because of knock.
^ Damaged ignition coils.
^ Blocked air filter or air intake.
^ Uneven compression.
^ Low fuel pressure.
^ Blocked exhaust system.
^ Faulty sensor signals.

TESTING PROCEDURE





Check Air Intake
^ Check air intake in front of radiator, air duct, Air Cleaner (ACL) housing and filter cartridge for blockage (leaves, paper, etc).

If OK:
- Proceed to: Check Preheater Damper, section below.
If blocked:
- Fix as necessary.





Check Preheater Damper
^ Engine at idle.
^ Place hand on preheater hose where it joins ACL.

Hose temperature should be same as ambient.

Hose at ambient temperature:
- Proceed to: Check Load Signal, section below.
Hose above ambient temperature:
- Check preheater damper in ACL for leakage.





Check Load Signal
^ Engine at idle.
^ Gear selector: neutral, A/C: OFF.
^ Power consumers such as Coolant Fan, heated rear window, etc. OFF.
^ Read off load signal.

Value should read 2.3 - 2.4 Volts.

If value OK:
- Proceed to: Check Spark Plug, section below.
If value differs:
- Fault trace Mass Air Flow (MAF) Sensor.
- See: DIAGNOSIS BY TROUBLE CODE / DTC 1-2-1 MAF SENSOR SIGNAL.





Check Spark Plug
^ Remove all spark plugs.
^ Check if any spark plug is lighter in color than the others.

If a spark plug is lighter-colored:
- This means that cylinder is being starved of fuel.
- Test with a new injection valve. Change all spark plugs.
If no spark plug is lighter in color than the others:
- Check compression.

NOTE: It is very important that the correct spark plugs are used. Also check gaps of new plugs before fitting. Spark plug gap should be 0.7 - 0.8 mm.





Check Compression
^ Carry out a compression test.

If compression OK:
- Proceed to: Check Fuel and Residual Pressure, section below.
If compression uneven:
- Fix as necessary.





Check Fuel and Residual Pressure
^ Check fuel and residual pressure.

If fuel and residual pressure OK:
- Proceed to: Check Engine Coolant Temperature, section below.
If fuel and residual pressure not OK:
- Fix as necessary.





Check Engine Coolant Temperature
^ Ignition ON.
^ Check if Engine Coolant Temperature (ECT) is OK.

ECT should read over 75°C (167°F) with warm engine, upper radiator hose should be OK.

If value OK:
- Proceed to: Check Catalysts and Exhaust System, section below.
If value differs:
- Check ECT sensor.





Check ECT Sensor
^ Ignition ON.
^ Connect multimeter P/N 9996525 to temperature box P/N 9995281 and temperature sensor P/N 9995282.

WARNING: RISK OF SCALDING.

^ Grip hose between radiator and thermostat housing with hose pliers; carefully bend it down and slack it off from the thermostat housing.





^ Insert sensor into thermostat housing and reinstall hose. It is important that the sensor is near the thermostat.
^ Read off temperature on multimeter.
^ Check that the Scan Tool (ST) reads the correct ECT. After checking, reinstall hose and expansion tank cover.

Value can vary by 5 - 10°C (10 - 20°F) because ECT sensor is mounted at rear of engine.

If the ST reads the correct ECT:
- Check cooling system.
If the ST reads incorrect ECT:
- Change ECT sensor.





Check Catalysts and Exhaust System
^ Check catalysts and exhaust system for blocked components.
^ Change blocked components as necessary.
^ Continue with: Check Knock, section below.





Check Knock
^ Abnormal knock may be due to any of the following fault sources, which are not listed in any particular fault-tracing order.

- Oil Induction
If the engine draws in oil through the crankcase ventilation system (possibly due to high engine oil level), combustion will be poor, resulting in knock.

- Defective spark plugs
Can cause poor combustion and, hence, knock.

- Loose / Defective Knock Sensor
Can provide incorrect knock information to ECM.

- Incorrect Fuel Grade
Can cause poor combustion and, hence, knock.

- Extremely High Engine / Air Temperature
Can cause poor combustion and, hence, knock.

- Incorrectly Adjusted Camshafts
If the camshafts are incorrectly adjusted, the intake and exhaust timing will be incorrect, causing poor combustion and, hence, knock.

- Mechanical Knock
Knock can also be due to worn mechanical components as for example excessive bearing clearance, piston fit, or valve chatter (defective hydraulic valve-lifters).

^ Fix as necessary.
^ Continue with: Connect Breakout Box, section below.





Connect Breakout Box
^ Connect breakout box and check control points.
^ Connect ECM.
^ Check all signals to and from ECM.