Isuzu Cars and Trucks 1981-1991

Exhaust Gas Recirculation System

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OPERATION

The EGR system lowers temperatures in the combustion chamber in order to reduce nitrogen oxide emissions in the exhaust gas stream. Exhaust gases are drawn from the cylinder head exhaust port through the intake manifold riser through the cylinder head, intake manifold and EGR valve passages. The EGR valve vacuum diaphragm is connected to the carburetor flange signal port through a thermal valve vacuum valve. The configuration controls the EGR cold override. When the throttle valve is opened, vacuum is applied to the EGR valve diaphragm which opens the valve, admitting a controlled amount of exhaust into the intake manifold.



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Fig. EGR system G180Z and G200Z carbureted engines



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Fig. EGR system 4XC1-U engine



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Fig. EGR system 4XC1-Turbo engine



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Fig. EGR system G200Z EFI engine



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Fig. EGR system 4ZC1-Turbo engine



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Fig. EGR system 4XE1 DOHC and SOHC engine



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Fig. EGR system 4ZE1 engine

SERVICE
Gasoline

G180Z and G200Z: The BP transducer is responsive to exhaust pressure. Under normal operating conditions, ported vacuum leaks into the atmosphere and is applied to the EGR valve under high pressure conditions.

To test the BPT, disconnect the hoses, blow air into the black colored hose at the lower side of the BPT, should be closed. Check to see if air passes through the signal hose on the opposite side and air filter side of BPT when tested by blowing air into the EGR side signal hose.

The thermal vacuum valve is mounted on the intake manifold and is connected in series between the vacuum port in the carburetor and EGR valve. While the coolant temperature is below 115129and#x00B0;F (4654and#x00B0;C) the valve is closed. Above that temperature, the valve is open.

To test the thermal vacuum valve; disconnect hoses, check that no continuity exists between the hoses when the engine is cold and that the passage opens after engine warm up.

4XC1-T: The vacuum switching valve overrides the EGR system when the engine is started cold. The valve blocks the vacuum signal to protect the EGR valve from excessive pressure from the turbocharger. The valve is controlled by the ECM (electronic control module).

The 4XC1-T engine uses the same BP transducer as does the G180Z and G200Z carbureted engine.

To test the EGR system, connect a tachometer to the engine and connect a vacuum gauge to the BPT, location A. Start the engine when cold, below 176and#x00B0;F (80and#x00B0;C). The vacuum gauge should read 0 at all engine speeds. Allow the engine to warm. The gauge should read 0 at idle and raise at 3500 rpm. Disconnect the vacuum gauge and connect it to the BPT. Make sure the EGR diaphragm operates properly when racing the engine up to 2000 rpm.



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Fig. EGR valve V6 engine



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Fig. Backpressure transducer G180Z, G200Z and 4XC1-T carb. engines, others similar



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Fig. Thermal vacuum valve G180Z, G200Z and 4XC1-U carb. engines, others similar



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Fig. Vacuum switching valve 4XC1-T engine



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Fig. Checking the EGR system 4XC1-T engine



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Fig. Vacuum switching valve 4ZC1-Turbo engine

4XE1, 4ZE1 and V6 engines: use the troubleshooting charts in this section.



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Fig. EGR troubleshooting chart 4XE1 engine



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Fig. EGR system check 4ZE1 engine



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Fig. EGR troubleshooting chart V6 engine

Diesel

4FB1 diesel (Calif.) engine: The EGR controller is mounted with the UQOS controller. The controller sends electrical ON-OFF signal to the vacuum switching valve according to coolant temperature, engine speed and injection pump control lever angle.

The engine speed sensor is mounted on the right side of the injection pump. The control lever position sensor is mounted on the front upper part of the injection pump. The resistance changes depending of lever position. The thermoswitch is mounted on the thermostat housing.

Testing: The EGR valve should hold constant vacuum at 13.8 in. Hg with a vacuum pump. Test the vacuum switching valve by applying 12V to the electrical terminals. Listen for plunger noise that is accompanied with electrical operation of the plunger. Connect a voltmeter to the black/green (+) and black/yellow (-) wire terminals at the vacuum switching valve. The controller is normal if the voltage is about 12V when the engine speed is above 1200 rpm. Test the thermo switch by submerging the switch in water and raise the temperature. Make a continuity test across the terminal and body using a circuit tester.

C223 diesel (Calif.) engine: The EGR controller is mounted with the UQOS controller. The controller sends electrical ON-OFF signal to the vacuum switching valve according to coolant temperature, engine speed and injection pump control lever angle.

Testing: The EGR valve should hold constant vacuum at 13.8 in. Hg with a vacuum pump. Test the vacuum switching valve by applying 12V to the electrical terminals. Listen for plunger noise that is accompanied with electrical operation of the plunger. To check the controller; connect a voltmeter to the green/black or green (+) and black/yellow (-) wire terminals at the vacuum switching valve. The controller is normal if the voltage is about 12V when the engine speed is below 3000 rpm. Test the thermoswitch by submerging the switch in water and raise the temperature to 115 and 19129and#x00B0;F (46 and 1954and#x00B0;C). Blow through the valve. Air should pass through the valve, if not replace the valve.



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Fig. EGR system 4FB1 diesel (California)



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Fig. Vacuum switching valve 4FB1 diesel (California only)



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Fig. EGR controller 4FB1 diesel (California only)



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Fig. EGR flow chart 4FB1 diesel engine



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Fig. Troubleshooting chart 1 4FB1 diesel engine



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Fig. Troubleshooting chart 2 4FB1 diesel engine



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Fig. EGR system C223 diesel (California only)



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Fig. EGR flow chart C223 diesel engine (California only)



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Fig. Troubleshooting chart 1 C223 diesel engine (California only)



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Fig. Troubleshooting chart 2 C223 diesel engine (California only)



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Fig. EGR controller and control lever position sensor C223 diesel engine (California only)

 
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