1988 JEEP CHEROKEE sensor

valve.
FORWARD DELAY VALVE
Forward delay valve is located between EGR CTO switch and EGR
valve. It modifies initial vacuum signal applied to EGR valve by
delaying full vacuum force.
TESTING
EGR VALVE
Valve Opening Test
1) With engine at normal operating temperature and at idle,
rapidly open and close throttle. Open throttle sufficiently to obtain
at least 1500 RPM. Movement should be noticed in EGR diaphragm.
2) If diaphragm does not move, probable causes are: faulty
vacuum signal to EGR, defective EGR diaphragm or defective
backpressure sensor diaphragm (if equipped), or leaks in vacuum lines
or connections.
Valve Closing Test
1) With engine at normal operating temperature and at idle,
manually depress EGR valve diaphragm. RPM should immediately drop,
indicating that EGR valve is not leaking and had been properly cutting
off exhaust gas flow at idle.
2) If there is no change in RPM and engine is idling
properly, exhaust gases are not reaching combustion chamber. Check for
plugged passage between EGR valve and intake manifold.
3) If engine idles poorly and RPM is not greatly affected by
manually moving diaphragm up, EGR valve is not closing off exhaust gas
flow. Check for carbon between pintle, leaking EGR valve gasket or bad
EGR valve.
COOLANT TEMPERATURE OVERRIDE (CTO) SWITCH
NOTE: Engine coolant temperature must be below 100F (38C) to
perform this test.
1) Check vacuum lines for leaks and correct routing.
Disconnect vacuum line at backpressure sensor (if equipped) or at EGR
valve, and attach this line to vacuum gauge.
2) Operate engine at 1500 RPM. No vacuum should be indicated
on gauge. If vacuum is shown, replace CTO switch.
3) Idle engine until coolant temperature exceeds 100
F (38C)
on 4-cylinder engines, or 115F (46C) on 6-cylinder and V8 engines.
4) Raise engine speed to 1500 RPM. Ported vacuum should be
shown on gauge. If not, replace CTO switch.
DUMP VALVE
1) With engine at normal operating temperature, remove dump
valve vacuum hose from manifold and plug manifold connection.
2) Raise engine speed to 2000 RPM. Vacuum should be present
at exhaust ports on bottom of valve. If not, replace valve.
3) Reconnect vacuum hose to manifold and raise engine speed
to 2000 RPM. No vacuum should be felt at exhaust ports on bottom of
valve. If vacuum is present, replace valve.
THERMAL VACUUM SWITCH (TVS)

SENDING UNITS & SENSORS









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Component Component Location
Automatic Load Leveling Sensor On top of left rear axle.
Brake Pad Wear Sensors In both inner front brake
pads.
Coolant Temp. Sending Unit/Switch
4-Cyl. On top left rear of cylinder
head.
6-Cyl. On top front of cylinder head.
Coolant Temperature Sensor

4-Cyl. (Graphic 2) In left rear side of intake
manifold.
6-Cyl. Left side of engine block,
under intake manifold
Engine Speed Sensor

Automatic Transmission On left side of torque
converter clutch.
Manual Transmission On left side of bellhousing.
Fluid Level Sensors
Brake Fluid In master cylinder.

Knock Sensor On lower front of engine.
Manifold Absolute Pressure
(MAP) Sensor In engine compartment, on
center of firewall.

Manifold Air Temperature
(MAT) Sensor (Graphic 1) On upper rear of intake
manifold.

Manifold Air Temperature
(MAT) Sensor (Graphic 2) On upper rear of intake
manifold.
Oil Pressure Sending Unit/Switch On right side of block, near
distributor.

Oxygen Sensor (Graphic 1) In exhaust manifold, near
exhaust pipe flange.
Oxygen Sensor (Graphic 2) In exhaust manifold, near
exhaust pipe flange.
Road Speed Sensor Under instrument cluster, in