Page 92
TROUBLESHOOTING
LOW POWER
Low power complaints may result from many
factors other than an engine problem. Be sure to
check the chassis and trailer for dragging brakes
and assess the drivetrain combination for
driveability and application (engine-rated bhp,
transmission and rear-axle ratios, tire sizes, etc.).
ENGINE WILL NOT ACHIEVE NO-LOAD GOVERNED RPM
Possible Cause Correction
1. Code(s) present. 1. Correct cause of code(s).
2. EGR valve-to-cooler pipe cracked or bellows
leaking. Causes low boost pressure.
2. Inspect EGR valve-to-cooler pipe and correct or replace leaking
component(s).
3. EGR valve sticking open. Causes low boost
pressure, poor performance.
3. Inspect EGR valve components for carbon fouled, soot buildup or
corrosion. Replace valve to correct.
4. Intercooler cracked or leaking. 4. Inspect intercooler, pressure-test, and repair or replace as
required.
5. Plugged fuel tank vents. 5. Clean the fuel tank vents.
6. Restrictions in the air intake system such as
clogged air filter(s).
6. Check for restrictions in the air intake system. Check the air
pressure in the air intake manifold. Replace the air filter and make
necessary repairs to the air intake system.
7. Poor quality fuel. 7. Drain fuel tank(s), clean system and replace fuel filters. Fill tank
with MACK-specified diesel fuel. Bleed system.
8. Low fuel pressure. 8. Check for sufficient fuel in the fuel tank. Check fuel filters (including
the pre-pump filter screen, if so equipped), replace if necessary.
Check fuel supply lines for restrictions or air in the system. Check
fuel return check valve for free-moving poppet. Check fuel
pressure and repair or replace supply pump as required.
9. Improper valve lash adjustment. 9. Adjust valve lash to specified clearance.
10. Fuel-injection nozzle failure. 10. Repair or replace defective nozzle. Refer to item 8 in ENGINE
MISFIRES — NO CODE(S) chart.
11. Turbocharger dirty or malfunctioning. 11. Inspect turbocharger. Clean, repair or replace as required.
12. Exhaust restriction. 12. Check for restrictions in the exhaust system.
13. Low compression. 13. Check items listed under LOW COMPRESSION.
14. Restrictions in intercooler. 14. Perform restriction pressure test. Clean any restrictions.
15. Restrictions in intercooler inlet/outlet tubes. 15. Disconnect tubing and clean restrictions.
16. Air cleaner-to-hood boot. 16. Check that the boot clamp on the air cleaner housing is tight, and
that the boot is making full contact with the hood and has not
collapsed.
Possible Cause Correction
1. Code(s) present. 1. Correct cause of code(s).
5-111.bk Page 92 Monday, July 10, 2006 2:26 PM
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