TROUBLESHOOTING
Page 79
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. 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.
3. Record the maximum boost pressure with
both housings (HI position).
4. Record the boost pressure with the switch in
the LO position.
LO position may be either front or rear housing.
5. Disconnect the LO position harness to the
solenoid and rerun the test with the switch in
the HI position. Record the results.
The individual housing readings will not be half of
the maximum boost pressure reading due to the
effect of the turbocharger. The individual boost
pressure readings, however, should be
approximately the same.
6. A significantly lower reading in one housing
indicates a possible problem with the
housing. Compare the maximum boost
pressure with the boost pressures in the
Table on page 78. A low reading indicates a
possible problem. Readings within 3 psi of
the values shown indicate proper operation
of the engine brake.
Electrical Troubleshooting
The J-Tech™ engine brake is activated by the
V-MAC
®
system. When the ignition switch is
turned ON, the engine brake solenoids are
supplied a constant 12-volt direct current with
current flow increasing whenever the engine
brake is activated. To properly diagnose electrical
problems with the brake, an ammeter may be
required.
If insufficient electrical power is reaching the
engine brake, perform the preliminary checks
outlined below. For more information, see the
V-MAC
®
III Service Manual, 8-211.
NO ENGINE BRAKE OPERATION
1. Check for a blown fuse or circuit breaker.
2. With electrical power OFF, check the control
system for a short to ground. Check systems
separately to isolate where the short is
occurring. If the control system is OK up to
the engine brake spacer connection,
measure the resistance to the solenoid
valve. High resistance means an open
circuit in the solenoid or solenoid wire.
ONLY ONE HOUSING OPERATING
1. Determine which housing is not operating by
closing all the switches and checking the
power at the wires leading to the solenoid
valves (front and rear).
2. Remove the wire to the solenoid valve at the
spacer and check for resistance (the Table
on page 80). No reading indicates an open
circuit in the wire or solenoid coil. A low
resistance reading indicates a short to
ground in the solenoid wire or solenoid coil.
A constant 12-volt low amperage signal is
supplied to the engine brake solenoids by the
V-MAC III module when the ignition switch is
turned on. During an engine braking event,
V-MAC increases the current to the solenoids to
activate the engine brake. The most accurate
method of checking electrical functionality of the
engine brake solenoids circuit is by using an
ammeter to measure current at the solenoids
when the engine brake is activated. When the
engine brake is activated, current should be
approximately 1.59 amps. For additional
information, consult the V-MAC
®
III Service
Manual, 8-211.
3. Test the solenoid by checking for current
draw and pull-in voltage per specifications
listed in the Table on page 80.
5_106_00.bk Page 79 Friday, August 4, 2000 11:17 AM
BDC for engine manuals and specs
https://barringtondieselclub.co.za/
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