User Manual

Page 9-4
200 TROUBLESHOOTING
ERRATIC ENGINE SPEED
200770a
When diagnosing low-power complaints, it is possible to trace the trouble to chassis
components rather than the engine. Make sure the chassis rolls freely when the
brakes are released.
LOW POWER
200771a
Possible Cause Correction
1. Air leaks in fuel suction line. 1. Check for air leaks. Repair as necessary.
2. Throttle linkage loose or out of adjustment. 2. Check throttle linkage. Repair or adjust as necessary.
3. Injection pump governor failure. 3. Remove injection pump and have it checked as follows by an
authorized MACK Fuel Injection System Repair facility:
— Check for damaged or broken springs or other components.
— Check for free travel of the fuel rack.
— Make sure the correct governor springs are installed.
— Repair or replace damaged parts as necessary.
— Recalibrate the injection pump and reinstall.
Possible Cause
Correction
1. Restrictions in the air-intake system such as a
clogged air filter(s).
1. Check the air pressure in the air-intake manifold. Replace the air
filter and make necessary repairs to the air system.
2. Poor quality fuel. 2. Drain fuel tank(s), clean system and replace fuel filters. Fill tank
with MACK-specified diesel fuel. Bleed system.
3. Damage or restrictions in the
accelerator/shut-off cable linkage.
3. Check linkage and adjust to achieve full travel. Replace if
damaged or bent.
4. Low fuel pressure. 4. Check fuel supply lines for kinks or restrictions. Check for air in
system. Check fuel pressure. If low, replace fuel filters. If still low,
replace or repair fuel transfer pump. Also check for sticking,
binding or defective fuel overflow valve. Repair or replace.
5. Improper valve lash adjustment. 5. Adjust valve lash to specified clearance.
6. Incorrect fuel injection timing. 6. Adjust fuel injection pump timing.
7. Plugged fuel tank vents. 7. Clean the fuel tank vents.
8. Fuel injection nozzle failure. 8. Isolate defective nozzle. Repair or replace.
9. Carbon or other friction-causing deposits in
turbocharger.
9. Inspect turbocharger. Clean, repair or replace as required.
10. Internal fuel injection pump wear which
prevents full rack travel.
10. Remove injection pump. Send the pump to an authorized MACK
Fuel Injection System Repair facility for repair and recalibration.
Then reinstall the pump.
11. High-altitude operation. 11. Engines lose horsepower with increases in altitude. The
percentage of power loss is governed by the altitude at which the
engine is operated. Make necessary adjustments.
12. Low boost pressure. 12. Check for restrictions in the air-intake system.
13. Exhaust restriction. 13. Check for restrictions in the exhaust system.
14. Low compression. 14. Check items listed for low compression.
15. Restrictions in cooler. 15. Perform restriction pressure test. Clean any restrictions.
16. Restrictions in cooler inlet or outlet tubes. 16. Disconnect tubing and clean restrictions.
17. Leaking cooler. 17. Repair or replace leaking cooler.
5-101.bk Page 4 Friday, March 17, 2006 11:05 AM