TROUBLESHOOTING
Page 111
ENGINE BRAKE TESTS (MACK
POWERLEASH™)
The ASET™ engines may be equipped with
either a MACK PowerLeash™ engine brake or a
J-Tech™ engine brake. The test procedures in
this section apply only to the MACK
PowerLeash™ engine brake.
Operational Tests
Before beginning the troubleshooting procedures,
try to determine the exact nature of the problem.
Talk to the driver, owner and/or mechanic to
pinpoint the complaint or problem. The following
checks may be helpful in trying to determine the
nature of the problem.
BEFORE STARTING THE ENGINE
If there is a report of engine or engine brake
noise, remove the cylinder head covers to
determine the cause. Check the following items:
1. Check for loose or broken components.
2. Check and verify valve and engine brake
plunger lash settings.
3. Check for bent push rods. If bent push rods
are found, check for possible bent valves,
and if the engine is equipped with ceramic
roller lifters, check for broken ceramic
rollers. Possible causes of bent valves or
push rods could be:
Engine overspeeding — Usually several
valves are affected.
One bent exhaust valve or push rod at a
single cylinder — This indicates the
possibility of incorrect valve adjustment. A
bent exhaust valve can also be caused by
the valve stem stuck in the guide, incorrect
valve, brake or yoke adjustment, or broken
or weak valve springs.
TEST DRIVE
Engine brake will not engage until coolant
temperature has reached 125°F (52°C).
1. Test drive the vehicle and measure intake
manifold boost pressure while operating the
engine brake. It is best to conduct the test
with a loaded vehicle, engine at
maximum-rated RPM and the engine brake
ON. Downhill operation is desirable to
stabilize RPM. Refer to the table on page
111 for boost pressures.
RETARDING BOOST PRESSURES (PSI) WITH MACK
POWERLEASH™ ENGINE BRAKE
If the vehicle does not have a boost pressure
gauge, one must be installed. A pipe plug is
located in the air inlet manifold for this purpose.
2. Record the maximum boost pressure with
the engine brake switch in the HIGH
position.
3. Record the boost pressure with the engine
brake switch in the LOW position.
LOW position may be either front or rear unit.
4. Disconnect the wire lead from the LOW
position terminal of the engine brake switch
and rerun the test with the switch in the
HIGH position. Record the results.
Engine Models: All AC Power Ratings
2100 rpm — 27 psi Boost
1900 rpm — 27 psi Boost
1700 rpm — 25 psi Boost
1500 rpm — 19 psi Boost
1300 rpm — 11 psi Boost
1100 rpm — 6 psi Boost
Note: Boost pressures may be less at high altitudes.
5-111.bk Page 111 Monday, July 10, 2006 2:26 PM
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