Mack ASET AC, Service Manual, Page: 128 / 536

TROUBLESHOOTING
Page 115
MACK PowerLeash™
Troubleshooting Guide
Following is a list of problem conditions showing
the probable causes and subsequent corrections.
ENGINE FAILS TO START OR STARTS AND
RUNS ONLY ON THREE CYLINDERS
앫
Solenoid valve stuck in ON position —
Ensure that electrical current is off to the
engine brake units. If the solenoid valve
remains on (cap down) with current off,
replace the solenoid valve.
앫
Solenoid valve O-ring missing or
damaged
— Replace as necessary.
앫
Solenoid not fully seated in rocker shaft
bore
— Remove the solenoid, inspect and
replace the O-rings as required. Reinstall
the solenoid to its full seated position before
snapping the retaining spring clips in place.
The clips must require a moderate force to
snap them around the rocker shaft and must
provide enough spring tension to prevent
any free movement of the solenoid or spring
clips. If spring clip tension cannot be
maintained, replace the clips.
ENGINE BRAKE WILL NOT OPERATE
앫
Blown fuse, open electrical leads — Look
for a short circuit in the wiring. Replace any
broken, brittle or chafed wires. Check
solenoid tab for signs of shorting and
replace if necessary. Replace 10 amp fuse.
앫
On/Off switch, clutch switch or
multi-position switch out of adjustment
or defective
— Use a volt/ohmmeter to
make certain that there is electrical voltage
available at both terminals of each switch.
Readjust if needed or replace if voltage will
not pass through switch.
Do not touch electrical connection when
system is energized.
앫
Mounting bracket-to-rocker shaft
mounting screws loose or missing
—
Inspect for missing or loose mounting
bracket-to-rocker shaft screws. Repair as
required.
앫
Blocked oil supply screen at front rocker
shaft mounting bracket
— Remove rocker
shaft assemblies and clean oil supply
screens.
앫
Incorrect electrical power source —
Check that the supply voltage is the
appropriate voltage. Recommended power
source is from the key switch ON position.
Ensure that power is not taken from a
source with an additional on/off switch, i.e.,
light switch. See solenoid specifications in
the table on page 113. Make sure wiring is in
accordance with MACK wiring instructions.
앫
Low engine oil pressure — Determine oil
pressure at engine brakes (solenoid valve
and control valve). If oil pressure is below
specification, the engine should be repaired
in accordance with MACK procedures.
앫
Brake lash not properly adjusted — The
engine brake units are very sensitive to
adjustment. Incorrect adjustment may hold
the valves open during positive power,
leading to engine failure, or may cause the
engine brake to work poorly or not at all.
Confirm that the engine brake is properly
adjusted in accordance with the table on
page 114.
ENGINE BRAKE ACTIVATES WITH
SWITCHES OPEN (OFF)
앫
Solenoid valve lower seal ring
damaged/missing
— Remove solenoid and
inspect lower O-ring for damage. Replace as
required.
앫
Engine brake improperly wired — Check
wiring in accordance with MACK wiring
diagrams.
앫
Control pistons binding in bore —
Remove control piston. If body is scored,
replace the control piston. Check for
contaminants in lube oil. Clean bore and
control piston. If binding continues, replace
rocker arm.
5-111.bk Page 115 Monday, July 10, 2006 2:26 PM