Ford 2003 Mustang Workshop Manual page 849

4. WORN RINGS OR DILUTED OIL: When the engine is accelerated (dotted needle), the needle
drops to 0 kPa (0 in-Hg). Upon deceleration, the needle runs slightly above 74 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 lash adjuster or hydraulic
lash adjuster (HLA) 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 over about a 13 kPa (4 in-Hg) range at idle
speed, the valve guides could be worn. As engine speed increases, the 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 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 are gapped too close, a regular, small
pulsation of the needle can occur.
13. INTAKE LEAK: A low, steady reading 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 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 (5230), kinked tail pipe 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.
16. 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.
Excessive Engine Oil Consumption
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