Poor Acceleration, Lack of Power

POOR ACCELERATION; LACK OF POWER

Conditions for Fault Tracing:
^ No DTCs present.
^ Engine hot.
^ Fault is permanent.

Fault Sources:
^ Timing retarded due to knock.
^ Faulty distributor cap / rotor.
^ Damaged ignition leads.
^ Blocked Air Cleaner (ACL) or air intake.
^ Leaking preheat damper.
^ Variable Intake System (V-VIS) fault.
^ Uneven compression.
^ Low fuel pressure.
^ Blockage in exhaust system.
^ Incorrect sensor signals.

TESTING PROCEDURE





Checking Timing Retardation Due to Knock
^ START engine.
^ Drive car and note value of retardation parameter (KN IGN RET).

If retardation due to knock remains continuously above 100 while acceleration is poor or engine displays lack of power, symptoms are probably due to retardation.

Retardation does not remain continuously above 10°:
- Proceed to: Checking Distributor Cap, Distributor Rotor and Ignition Leads.
Retardation is continuously above 10°:
- Proceed to: Checking for Knock, section below.





Checking Distributor Cap, Distributor Rotor and Ignition Leads
^ Switch OFF ignition.
^ Check distributor cap, distributor rotor and ignition leads for damage, cracking or arcing. Replace faulty components as needed.

- Proceed to: Checking of Fuel Trim at Idling.








Checking Long Term Fuel Trim at Idling
^ START engine and allow to idle.
^ Display and read value of long term fuel trim at idling.

Value should be less than +15.

If reading is correct:
- Proceed to: Checking Preheat Damper.
If reading is incorrect:
- Check tightness of air intake and ACL.








Checking Preheat Damper
^ Switch OFF ignition.
^ Disconnect fresh air tube from ACL housing.
^ Check that damper is in cold air position.

If damper position is correct:
- Proceed to: Checking V-VIS System.
If damper position is incorrect:
- Establish why damper is not in correct position.

- Damper should be in cold air position when damper thermostat is set to approx. 20°C (68°F).
- Adjust damper as required.





Checking V-VIS System
^ Check V-VIS system.

See: DIAGNOSIS BY SYMPTOM / OTHER ELECTRICAL FAULT TRACING / CHECKING VARIABLE INTAKE SYSTEM (V-VIS).

If V-VIS is operating correctly:
- Proceed to: Checking Compression.
If V-VIS is not operating correctly:
- Repair as required.





Checking Compression
^ Check engine compression.

If compression is correct:
- Proceed to: Checking fuel pressure.
If compression is uneven:
- Repair as required.





Checking Fuel Pressure
^ Check fuel pressure and residual pressure.

See: FUEL DELIVERY AND AIR INDUCTION / FUEL PRESSURE / TESTING AND INSPECTION / FUEL PRESSURE AND RESIDUAL PRESSURE TESTING.

If fuel pressure and residual pressure are correct:
- Proceed to: Checking Exhaust System.
If fuel pressure and residual pressure are incorrect:
- Repair as required.





Checking Exhaust System
^ Check exhaust system and Three-Way Catalytic Converter (TWC) for blockage.

If exhaust system is clear:
- Proceed to: Connecting Test Box.
If exhaust system is blocked:
- Repair as required.





Connecting Test Box
^ Connect test box to Distributor Ignition (DI) System and check ground terminals.
^ Plug Ignition Control Module (ICM) into test box adapter.
^ Check all signals to and from the (MFI) Engine Control Module and the (ICM) Ignition Control Module.

See: COMPUTERS AND CONTROL SYSTEMS / TESTING AND INSPECTION / DIAGNOSTIC CHARTS / NON-TROUBLE CODE CHARTS / ECM PINOUT & TERMINAL I.D. CHARTS.

Checking for Knock
^ Abnormal knock may be due to any one of the following reasons (which are not listed in any particular 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).





^ Faulty spark plugs/ignition leads.
May cause poor combustion, resulting in knock.

^ Faulty distributor cap/rotor.
May cause poor combustion, resulting in knock.





^ Loose/faulty knock sensor.
May supply ICM with incorrect knock signal.

^ Incorrect fuel grade.
May cause poor combustion, resulting in knock.

^ Extremely high engine/air temperature.
May cause poor combustion, resulting in knock.

^ Incorrectly adjusted camshafts.
The intake and exhaust valve opening periods will be incorrect if the camshafts are incorrectly adjusted. The timing will also be altered since the distributor is mounted at the rear of the camshaft. This may cause poor combustion, resulting in knock.





^ Mechanical knock.
Mechanical knock may be due to worn mechanical components, resulting in excessive bearing clearance, excessive piston clearance or valve noise (faulty hydraulic tappets).