McQue
NAXJA Forum User
- Location
- Plainville, Connecticut
Found this write-up about troubleshooting motors with a vacumn guage...
Caused me to go looking for manufacturer specs on vacumn in my FSM...could not find them.. So...a couple of questions...
1. Any body have vacumn specs for an 01XJ at idle, and at 2000 RPM?
( or at least a ballpark range educated guess)
2. Do you buy off on the following write up as valid?
Diagnosing car engines with a vacuum gauge. A vacuum gauge gives
a quick and cheap (under $15) indication of engine problems. To
isolate a problem further diagnostics are usually needed.
This is a consolidation of diagnostics from three sources:
1. instructions for Equus vacuum gauge
2. Chilton general car care manual
3. Haynes emissions control manual
Connecting the vacuum gauge.
Engine must be warm or the gauge reading will be too high and
computer will be in warmup mode. Select a vacuum hose connected
directly to the car's intake manifold or select an unused port on
the manifold. The best alternative would be to attach a hose to
an unused port on the manifold and leave it there for use with
the gauge. Plug the hose when not in use. Otherwise if in doubt
which hoses are connected to the intake manifold, consult the
hose diagram on the emissions sticker, usually found on the
underside of the hood or on the firewall, or consult a repair
manual. If still in doubt the hose to the MAP (pressure) sensor
is connected directly to the intake manifold. The gauge can be
tapped into a hose using a T-connector. For a quick and dirty
reading unplug the easy to find PCV hose on the valve cover and
plug in the vacuum gauge. Using the PCV hose may not give a
direct connection to the intake manifold and it will cause the
engine to idle slowly, but it will give an intake vacuum reading
and is easy to use when looking at a strange car, for example a
prospective purchase. Start the engine and read the gauge in
inches of mercury (in Hg). The dial on the gauge may be marked
with the good range.
1. Equus instructions
a. testing at idle speed
- compare vacuum reading with manufacturer's specification.
- a lower reading indicates possible incorrect timing,
incorrect valve timing or adjustment, incorrect setting of
idle mixture, worn piston rings, or leak in intake
manifold.
- readings that change slowly indicate incorrect setting of
idle mixture screw.
- readings that change quickly indicate sticky valve guides,
burned valve sets, or leak in head gasket.
b. testing at 2000 rpm
- a lower reading indicates possible restriction in exhaust.
- oscillating reading indicates possible weak valve springs.
2. Chilton general car care manual.
- gauge reading steady 17-22 in Hg indicates normal engine in
good condition.
- gauge reading low (15-20 in Hg) but steady indicates late
ignition or valve timing, low compression, stuck throttle
valve, leaking carburetor or manifold gasket.
- gauge reading steady but dropping regularly indicates burnt
valve or improper valve clearance.
- gauge reading dropping gradually at idle indicates choked
muffler or obstruction in exhaust.
- gauge reading slowly dropping to zero as engine speeds up
indicates choked muffler.
- gauge reading fluctuating between 15 and 20 in Hg at idle
indicates stuck valve or ignition miss.
- gauge reading drifting indicates improper carburetor
adjustment or minor intake leak at carburetor or manifold.
- gauge reading fluctuating as engine speed increases
indicates weak valve springs, worn valve stem guides.
- gauge reading vibrating excessively at idle but steady as
engine speeds up indicates worn valve guides.
- gauge reading vibrating excessively at all speeds indicates
leaky cylinder head gasket.
3. Haynes emissions control manual
a. testing at various speeds
- engine starting vacuum should be 1 to 4 in Hg. To test
disable ignition (ground wire from coil), hold throttle
wide open, crank engine slowly with starting motor.
- healthy engine at idle should read steady 15 to 20 in Hg.
- healthy engine at 2000 rpm should read steady 19 to 21 in
Hg.
- healthy engine at open throttle should read close to 0 in
Hg.
- healthy decelerating engine reading should jump to 21 to
27 in Hg as open throttle released.
b. testing at idle speed
- low steady reading usually indicates leaking gasket
between intake manifold and carburetor or throttle body,
leaky vacuum hose, or incorrect camshaft timing.
- low fluctuating (3 to 8 in Hg below normal) reading may
indicate intake manifold gasket leak at an intake port or
faulty injectors on port-injected engines.
- regular drops (2 to 4 in Hg) in reading at a steady rate
indicates probable leaking valves.
- irregular drops in reading indicates possible sticking
valve or ignition misfire.
- rapid vibration (4 in Hg) in reading combined with exhaust
smoke indicates worn valve guides.
- slight fluctuation (1 in Hg) in reading indicates possible
ignition problems.
- large fluctuation (10 in Hg) in reading indicates likely
weak or dead cylinder or blown head gasket.
- slow movement through wide range in reading indicates
possible clogged PCV system, incorrect idle fuel mixture,
or gasket leak between carburetor, throttle body, or
intake manifold.
c. testing at higher speeds
- rapid vibration (4 in Hg) in reading at increased engine
speed indicates leaking intake manifold gasket or head
gasket, weak valve springs, burned valves, or ignition
misfire.
- reading returns slowly to normal and didn't peak above
normal (5 in Hg) after dropping to zero when throttle
quickly snapped open (2500 rpm) suspect worn rings.
- reading returns to normal after long delay when throttle
quickly snapped open (2500 rpm) suspect blocked exhaust.
d. testing for blocked exhaust
- idle speed reading slowly dropping toward zero indicates
exhaust restriction.
- excessive backpressure in exhaust then indicated by
reading not increasing quickly to about 16 in Hg when
engine speed slowly increased to 2000 rpm.
- backpressure also indicated by reading not dropping as
quickly when throttle quickly released and remaining 5 in
Hg higher or more than normal.
- disconnect exhaust manifold from engine and retest. If
problem disappears exhaust system is blocked.
- to locate restriction reconnect exhaust system one unit at
a time testing after each until problem reappears.
---------------------------------------------------------------
Caused me to go looking for manufacturer specs on vacumn in my FSM...could not find them.. So...a couple of questions...
1. Any body have vacumn specs for an 01XJ at idle, and at 2000 RPM?
( or at least a ballpark range educated guess)
2. Do you buy off on the following write up as valid?
Diagnosing car engines with a vacuum gauge. A vacuum gauge gives
a quick and cheap (under $15) indication of engine problems. To
isolate a problem further diagnostics are usually needed.
This is a consolidation of diagnostics from three sources:
1. instructions for Equus vacuum gauge
2. Chilton general car care manual
3. Haynes emissions control manual
Connecting the vacuum gauge.
Engine must be warm or the gauge reading will be too high and
computer will be in warmup mode. Select a vacuum hose connected
directly to the car's intake manifold or select an unused port on
the manifold. The best alternative would be to attach a hose to
an unused port on the manifold and leave it there for use with
the gauge. Plug the hose when not in use. Otherwise if in doubt
which hoses are connected to the intake manifold, consult the
hose diagram on the emissions sticker, usually found on the
underside of the hood or on the firewall, or consult a repair
manual. If still in doubt the hose to the MAP (pressure) sensor
is connected directly to the intake manifold. The gauge can be
tapped into a hose using a T-connector. For a quick and dirty
reading unplug the easy to find PCV hose on the valve cover and
plug in the vacuum gauge. Using the PCV hose may not give a
direct connection to the intake manifold and it will cause the
engine to idle slowly, but it will give an intake vacuum reading
and is easy to use when looking at a strange car, for example a
prospective purchase. Start the engine and read the gauge in
inches of mercury (in Hg). The dial on the gauge may be marked
with the good range.
1. Equus instructions
a. testing at idle speed
- compare vacuum reading with manufacturer's specification.
- a lower reading indicates possible incorrect timing,
incorrect valve timing or adjustment, incorrect setting of
idle mixture, worn piston rings, or leak in intake
manifold.
- readings that change slowly indicate incorrect setting of
idle mixture screw.
- readings that change quickly indicate sticky valve guides,
burned valve sets, or leak in head gasket.
b. testing at 2000 rpm
- a lower reading indicates possible restriction in exhaust.
- oscillating reading indicates possible weak valve springs.
2. Chilton general car care manual.
- gauge reading steady 17-22 in Hg indicates normal engine in
good condition.
- gauge reading low (15-20 in Hg) but steady indicates late
ignition or valve timing, low compression, stuck throttle
valve, leaking carburetor or manifold gasket.
- gauge reading steady but dropping regularly indicates burnt
valve or improper valve clearance.
- gauge reading dropping gradually at idle indicates choked
muffler or obstruction in exhaust.
- gauge reading slowly dropping to zero as engine speeds up
indicates choked muffler.
- gauge reading fluctuating between 15 and 20 in Hg at idle
indicates stuck valve or ignition miss.
- gauge reading drifting indicates improper carburetor
adjustment or minor intake leak at carburetor or manifold.
- gauge reading fluctuating as engine speed increases
indicates weak valve springs, worn valve stem guides.
- gauge reading vibrating excessively at idle but steady as
engine speeds up indicates worn valve guides.
- gauge reading vibrating excessively at all speeds indicates
leaky cylinder head gasket.
3. Haynes emissions control manual
a. testing at various speeds
- engine starting vacuum should be 1 to 4 in Hg. To test
disable ignition (ground wire from coil), hold throttle
wide open, crank engine slowly with starting motor.
- healthy engine at idle should read steady 15 to 20 in Hg.
- healthy engine at 2000 rpm should read steady 19 to 21 in
Hg.
- healthy engine at open throttle should read close to 0 in
Hg.
- healthy decelerating engine reading should jump to 21 to
27 in Hg as open throttle released.
b. testing at idle speed
- low steady reading usually indicates leaking gasket
between intake manifold and carburetor or throttle body,
leaky vacuum hose, or incorrect camshaft timing.
- low fluctuating (3 to 8 in Hg below normal) reading may
indicate intake manifold gasket leak at an intake port or
faulty injectors on port-injected engines.
- regular drops (2 to 4 in Hg) in reading at a steady rate
indicates probable leaking valves.
- irregular drops in reading indicates possible sticking
valve or ignition misfire.
- rapid vibration (4 in Hg) in reading combined with exhaust
smoke indicates worn valve guides.
- slight fluctuation (1 in Hg) in reading indicates possible
ignition problems.
- large fluctuation (10 in Hg) in reading indicates likely
weak or dead cylinder or blown head gasket.
- slow movement through wide range in reading indicates
possible clogged PCV system, incorrect idle fuel mixture,
or gasket leak between carburetor, throttle body, or
intake manifold.
c. testing at higher speeds
- rapid vibration (4 in Hg) in reading at increased engine
speed indicates leaking intake manifold gasket or head
gasket, weak valve springs, burned valves, or ignition
misfire.
- reading returns slowly to normal and didn't peak above
normal (5 in Hg) after dropping to zero when throttle
quickly snapped open (2500 rpm) suspect worn rings.
- reading returns to normal after long delay when throttle
quickly snapped open (2500 rpm) suspect blocked exhaust.
d. testing for blocked exhaust
- idle speed reading slowly dropping toward zero indicates
exhaust restriction.
- excessive backpressure in exhaust then indicated by
reading not increasing quickly to about 16 in Hg when
engine speed slowly increased to 2000 rpm.
- backpressure also indicated by reading not dropping as
quickly when throttle quickly released and remaining 5 in
Hg higher or more than normal.
- disconnect exhaust manifold from engine and retest. If
problem disappears exhaust system is blocked.
- to locate restriction reconnect exhaust system one unit at
a time testing after each until problem reappears.
---------------------------------------------------------------
