Jeep Cherokee 2000 Service Manual - page 1953
When the variable ground signal is supplied to the
EVM, vacuum from the vacuum pump will be
allowed to pass through the EVM and on to the EGR
valve with a connecting hose.
Exhaust gas recirculation will begin in this order
when:
•
The ECM determines that EGR system opera-
tion is necessary.
•
The engine is running to operate the vacuum
pump.
•
A variable ground signal is supplied to the EVM.
•
Variable vacuum passes through the EVM to the
EGR valve.
•
The inlet seat (poppet valve) at the bottom of
the EGR valve opens to dilute and recirculate
exhaust gas back into the intake manifold.
The EGR system will be shut down by the ECM
after 60 seconds of continuous engine idling to
improve idle quality.
DIAGNOSIS AND TESTING
EGR GAS FLOW TEST
Refer to the 2000 XJ Diesel Powertrain Diagnostic
Manual for complete test procedure.
EGR SOLENOID TEST
VACUUM TEST
With the engine running, disconnect the vacuum
supply line at the fitting on the Electric Vacuum
Modulator (EVM). Vacuum should be no less than 20
inches. If vacuum is lower, check for leaks in vacuum
supply line. If leaks cannot be found, check for low
vacuum at vacuum pump.
REMOVAL AND INSTALLATION
EGR VALVE
REMOVAL
(1) Disconnect vacuum line at EGR valve vacuum
supply fitting.
(2) Loosen the tube fitting at exhaust manifold end
of EGR tube.
(3) Remove the two bolts retaining the EGR tube
to the EGR valve and remove the EGR tube.
(4) Remove the two bolts retaining the EGR valve
to the intake manifold elbow and remove EGR valve.
(5) Discard both of the old EGR mounting gaskets.
INSTALLATION
(1) Clean the intake manifold of any old gasket
material.
(2) Clean the end of EGR tube of any old gasket
material.
(3) Position the EGR valve and new gasket to the
intake manifold elbow.
(4) Install two EGR valve mounting bolts. Do not
tighten bolts at this time.
(5) Position new gasket between EGR valve and
EGR tube.
(6) Install two EGR tube bolts. Tighten all four
mounting bolts to 23 N·m (204 in. lbs.).
(7) Tighten EGR tube fitting at exhaust manifold.
(8) Connect vacuum line to EGR valve.
EGR TUBE
The EGR tube connects the EGR valve to the rear
of the exhaust manifold.
REMOVAL
(1) Remove two EGR tube mounting bolts at EGR
valve end of tube.
(2) Loosen fitting at exhaust manifold end of tube.
(3) Remove EGR tube and discard old gasket.
(4) Clean gasket mating surfaces and EGR tube
flange gasket surfaces.
(5) Check for signs of leakage or cracked surfaces
at both ends of tube, exhaust manifold and EGR
valve.
INSTALLATION
(1) Install a new gasket to EGR valve end of EGR
tube.
(2) Position EGR tube to engine.
(3) Loosely tighten fitting at exhaust manifold end
of tube.
(4) Install 2 mounting bolts at EGR valve end of
tube. Tighten bolts to 23 N·m (204 in. lbs.) torque.
(5) Tighten fitting at exhaust manifold end of tube.
Fig. 2 Internal Vacuum Pump
1 – INTERNAL VACUUM PUMP AND DRIVE GEAR
XJ
EMISSION CONTROL SYSTEM
25 - 7
DESCRIPTION AND OPERATION (Continued)