Mityvac MI8000 Manual Del Usuario página 8

DiaGnosinG mechanicaL enGine conDitions
BLOWN CYLINDER HEAD GASKET
At idle, the vacuum pump gauge pointer will
fluctuate between normal and a low reading.
The needle will drop sharply about 340 mbar (10"
Hg) from a normal reading and return each time
the defective cylinder or cylinders reach firing position.
EXHAUST RESTRICTION TEST
An exhaust restriction will cause normal or near nor-
mal performance at engine idle, but cause very poor
engine performance under load or at higher speeds.
1) Connect the pump hose to an intake manifold
vacuum fitting. Operate the engine at idle and
note the vacuum reading and needle movement.
Compare readings and movements against
descrip tions listed for burned valves and late
ignition or valve timing.
2) Watch the vacuum gauge as engine speed is
increased to approximately 2500 RPM.
3) An increase in vacuum over that obtained at idle
indicates an exhaust system that is free of restrictions.
4) If the needle drops toward zero as engine RPM
is increased, either an exhaust restriction or an
over-active Exhaust Gas Recirculation (EGR) valve
is causing the problem.
5) Test the EGR valve separately. If it is found to
be in good condition, the problem is a restricted
exhaust. Check and replace if necessary.
INCORRECT IDLE AIR/FUEL MIXTURE
If the gauge needle drifts slow ly back and forth at
idle, over a range of 135 to 170 mbar (4 to 5" Hg),
the fuel mixture is too rich. A lean mixture will cause
an irregular drop of the needle over about the same
range.
Page Number - 8
INTAKE MANIFOLD OR AIR INDUCTION
LEAKS
If there are any air leaks in the air induction
system, the gauge needle will be about 100 to 300
mbar (3 to 9" Hg) below normal, but will remain
steady.
LATE IGNITION OR VALVE TIMING
An extremely low but steady reading at idle
indicates late ignition or valve timing, or a
uniformly close setting of the valve lash.
Perform separate tests to determine which
of these problems, if any, have affected
the engine.
Form 824357