Chrysler RAM TRUCK 2500 1994 Service Manual page 180

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POWER BRAKE VACUUM PUMP (DIESEL MODELS) i - 21
Fig. 2 Diesel Vacuum Switch Location (Without
ABS)
connects the switch sensor to the brake warning
light. I f booster vacuum falls below 8.5 inches for
8-10 seconds or more, the switch sensor completes
the circuit to the warning light causing i t to illumi­
nate.
VACUUM PUMP DIAGNOSIS
Vacuum pump diagnosis involves checking pump
output with a vacuum gauge. The low vacuum warn­
ing switch can also be checked with a vacuum gauge.
Refer to the diagnosis procedure i n this section.
A standard vacuum gauge can be used to check
pump output when necessary. Simply disconnect the
pump supply hose and connect a vacuum gauge to
the outlet port for testing purposes. Vacuum should
hold steady i n a range of approximately 8.5 to 25
inches at various engine speeds.
DIAGNOSING LOW VACUUM OUTPUT
CONDITION
A low booster vacuum condition or a faulty low vac­
uum warning switch will cause the brake warning
light to illuminate. I f the light does go on and indi­
cates the existence of a low vacuum condition, check
the vacuum pump, booster and warning switch as fol­
lows:
(1) Check vacuum pump oil feed line. Verify that
line connections are secure and not leaking. I f leak­
age is noted and pump is noisy, replace pump.
(2) Disconnect supply hose to booster. Connect vac­
uum gauge to this hose and run engine at various
throttle openings. Output should range from 8.5 to
25 inches vacuum. I f vacuum is consistently below
8.5 inches, problem is with vacuum hoses or pump
component. I f output is within specified limits, con­
tinue testing.
(3) Check booster operation as described i n diagno­
sis section. Replace check valve, vacuum hoses, or
booster i f necessary. However, i f booster operation is
correct but warning light is still on, continue testing.
(4) Disconnect vacuum hose at warning switch.
Plug hose and connect hand vacuum pump to switch.
(5) Start and run engine.
(6) Apply 8.5 to 9 inches of vacuum to warning
switch and observe warning light. I f light goes out,
switch vacuum hose is either loose or leaking. I f light
remains on, leave engine running and continue test­
ing.
(7) Apply 20-25 inches vacuum to switch and ob­
serve warning light operation. I f light now goes out,
switch is at fault and should be replaced. I f light re­
mains on, continue testing.
(8) Reconnect vacuum hoses and replace original
warning switch with known good switch. Run engine
and observe warning light operation. I f light is now
off, old switch is faulty. I f light remains on, problem
is i n wiring between switch and warning light.
VACUUM—STEERING PUMP ASSEMBLY REMOVAL
(1) Disconnect battery negative cable.
(2) Position drain pan under power steering pump.
(3) Disconnect vacuum and steering pump hoses
from respective pumps (Pig. 3).
Fig. 3 Vacuum And Steering Pump Hose
Connections
(4) Disconnect oil pressure sender wires at sender
(Fig. 4).
(5) Remove oil pressure sender (Fig. 4).
(6) Disconnect lubricating oil feed line from fitting
at underside of vacuum pump (Fig. 5).
(7) Remove lower bolt that attaches pump assem­
bly to engine block (Fig. 6).