03-oo-10
Engine-Service
03-oo-1 0
SERVICE PROCEDURES (Continued)
The following are potential gauge readings. Some are
normal; others should be investigated further.
3
4
5
10
12
13
14
15
A23315-A
1.
NORMAL READING: Needle between
51-7 4
kPa
(15-22
in-Hg) and holding steady.
2.
NORMAL READING DURING RAPID
ACCELERATION AND DECELERATION: When
engine is rapidly accelerated (dotted needle),
needle will drop to a low (not to zero) reading.
When throttle is suddenly released, the needle
will snap back up to a higher than normal figure.
3.
NORMAL FOR HIGH-LIFT CAMSHAFT WITH
LARGE OVERLAP: Needle will register as low as
51
kPa (
15
in-Hg) but will be relatively steady.
Some oscillation is normal.
4.
WORN RINGS OR DILUTED OIL: When engine is
accelerated (dotted needle), needle drops to
0
kPa
(0
in-Hg). Upon deceleration, needle runs
slightly above
7 4
kPa
(22
in-Hg).
5.
STICKING VALVES: When the needle (dotted)
remains steady at a normal vacuum but
occasionally flicks (sharp, fast movement) down
and back about
13
kPa
(4
in-Hg), one or more
valves may be sticking.
6.
BURNED OR WARPED VALVES: A regular,
evenly-spaced, downscale flicking of the needle
indicates one or more burned or warped valves.
Insufficient hydraulic valve tappet clearance will
also cause this reaction.
7. POOR VALVE SEATING: A small but regular
downscale flicking can mean one or more valves
are not seating.
8. WORN VALVE GUIDES: When the needle
oscillates (swings back and forth), over about a
13
kPa
(4
in-Hg) range at idle speed the valve
guides could be worn. As engine speed
increases, needle will become steady
if
guides
are responsible.
9. WEAK VALVE SPRINGS: When the needle
oscillation becomes more violent as engine rpm is
increased, weak valve springs
(6513)
are
indicated. The reading at idle could be relatively
steady.
10.
LATE VALVE TIMING: A steady but low reading
could be caused by late valve timing.
11.
IGNITION TIMING RETARDING: Retarded ignition
timing will produce a steady but somewhat low
reading.
12.
INSUFFICIENT SPARK PLUG GAP: When spark
plugs
(12405)
are gapped too close, a regular,
small pulsation of the needle can occur.
13.
INTAKE LEAK: A low, steady reading which can
be caused by an intake manifold or throttle body
gasket leak.
14.
BLOWN HEAD GASKET: A regular drop of fair
magnitude can be caused by a blown head
gasket
(6051)
or warped cylinder
head-to-cylinder block surface.
15.
RESTRICTED EXHAUST SYSTEM: When the
engine is first started and is idled, the reading
may be normal but as the engine rpm is
increased, the back pressure caused by a
clogged muffler, kinked tailpipe or other
concerns, will cause the needle to slowly drop to
0
kPa
(0
in-Hg). The needle then may slowly rise.
Excessive exhaust clogging will cause the needle
to drop to a low point even if the engine is only
idling.
When vacuum leaks are indicated, search out and
correct the cause. Excess air leaking into the
system will upset the fuel mixture and cause
concerns such as rough idle, missing on
acceleration or burned valves.
If
the leak exists in
an accessory unit such as the power brake
booster
(2005),
the unit will not function correctly.
ALWAYS FIX VACUUM LEAKS.
Engine Oil Consumption, Excessive
The amount of oil an engine uses will vary with the way
the vehicle is driven in addition to normal
engine-to-engine variation. This is especially true
during the first
16,100
km
(10,000
miles) when a new
engine is being broken in or until certain internal engine
components become conditioned. Vehicles used in
heavy-duty operation may use more oil. The following
are examples of heavy-duty operation:
•
trailer towing applications
•
severe loading applications
•
sustained high speed operation
1997 Thunderbird, Cougar July 1996
