Ported EGR Valve
- Check vacuum hoses for correct routing. Connect a vacuum gauge directly to EGR vacuum source. With engine running, open throttle. If gauge indicates vacuum, EGR vacuum supply is okay.
- If gauge indicates no vacuum, EGR vacuum port is plugged. Disconnect vacuum hose at EGR valve, and plug hose. Connect a vacuum pump to EGR valve.
- Start engine. Apply 6-10 in. Hg to EGR valve. Engine should run rough or stall and EGR valve should hold vacuum. If engine speed does not change, check for plugged EGR passages or faulty EGR valve.
Backpressure Transducer EGR System
- Check vacuum hoses for correct routing. Connect a vacuum gauge directly to EGR vacuum source on carburetor. With engine running, open and close throttle. If vacuum is present, EGR vacuum port is open.
- If no vacuum is present, EGR vacuum port is plugged. Disconnect EGR supply hose from EGR valve. Connect a vacuum pump to EGR valve. With engine at normal operating temperature and at 2000-2500 RPM, slowly apply 8 in. Hg to EGR valve. EGR valve stem should move up, oscillate and move down with throttle movement. Release vacuum and engine speed should increase.
- If operation is not as specified, check for plugged EGR passages or faulty EGR valve.
Integral Backpressure Transducer Assembly
- Check vacuum hose routing. Disconnect EGR valve hose, and connect vacuum gauge to hose. With engine warm, vacuum to EGR valve should exist at 2000-3000 RPM. If vacuum does not exist, check vacuum lines from EGR valve to source.
- Clamp a plug (freeze plug may be used) into end of tailpipe; plug should be about 1/16" less than I.D. Connect vacuum pump to EGR valve. DO NOT disconnect transducer from EGR valve.
- Idle engine and gradually apply 6-10 in. Hg. EGR valve stem/diaphragm should move smoothly and engine speed should drop at least 100 RPM.
Electronic EGR Valve
- Connect vacuum gauge to EGR valve. Start engine. Ensure there is less than one in Hg to EGR valve at idle with engine at normal operating temperature. NOTE: EGR Vent Solenoid (EVRV) allows a small vacuum signal (less than 2.5 in. Hg) at idle.
- Install tachometer. Disconnect Idle Air By-Pass Valve (IABV) harness connector (if equipped). Disconnect and plug vacuum hose to EGR valve. Start engine and idle in Neutral. Note idle speed. Using a hand-held vacuum pump, slowly apply 5-10 in. Hg to EGR valve.
- Engine should either stall or idle should drop at least 100 RPM. Idle speed should return to normal when vacuum is released at EGR valve. Repair or replace EGR valve if none of the conditions occur.
Vacuum Amplifier (If Equipped)
- Ensure manifold vacuum is okay. With engine warm and idling, connect vacuum gauge to port "O" (leads to EGR ported vacuum switch) on vacuum amplifier. Vacuum should not read more than 2 in. Hg at idle.
- Disconnect venturi hose at carburetor/throttle body. Increase engine speed to 3000 RPM on 2.3L engines or 2000 RPM on all other engines. Vacuum should not change. Maintain high engine speed and reconnect venturi hose.
- Vacuum gauge should register at least 4 in. Hg. Return engine to idle. Vacuum gauge should return to initial reading. If vacuum gauge does not return to initial reading, replace vacuum amplifier.
EEC-V Equipped Vehicles
- Turn ignition off. Disconnect and plug vacuum hose at EGR valve. Connect a hand-held vacuum pump to EGR valve. Connect scan tool to DLC.
- Start engine and bring to operating temperature. Allow engine to idle. Adjust scan tool to read EGR Differential Pressure Feedback Sensor voltage.
- Slowly apply 5-6 in. Hg to EGR valve and hold for 10 seconds. Keep engine RPM at 800 RPM.
- As vacuum increases, voltage should rise to about 2.5 volts. When vacuum is held steady, voltage should hold steady.
- If EGR does not hold vacuum, check for defective EGR valve. If Differential Sensor Pressure Feedback Sensor voltage is not as specified, check for defective sensor. Also check for blocked EGR passages.
1996-97 EEC-IV Equipped Trucks
- Ensure all vacuum hoses are correctly routed and securely attached. Replace any crimped or broken hoses. Ensure less than one in. Hg vacuum to EGR valve exists at idle with engine at normal operating temperature.
- Install tachometer. Disconnect idle air by-pass valve electrical connector (if equipped). Remove and plug vacuum hose at EGR valve. Start engine, and idle it in Neutral. Note idle speed. Using vacuum pump, apply 5-10 in. Hg to EGR valve. When vacuum is fully applied to EGR, one or more of following should occur: Engine should stall. Idle speed should drop greater than 100 RPM. Idle speed should return to normal when vacuum is released.
- Repair or replace EGR valve if engine does not respond as specified. Reconnect idle air by-pass valve electrical connector. Unplug and reconnect vacuum hose at EGR valve.
EGR Valve
- Ensure all vacuum hoses are correctly routed and securely attached. Replace any crimped or broken hoses. Ensure there is less than one in. Hg vacuum to EGR valve at idle with engine at normal operating temperature.
- Install tachometer. Disconnect Idle Air Control (IAC) wiring harness connector. Remove and plug vacuum hose at EGR valve. Start engine and allow to idle in Neutral. Note idle speed. Using hand vacuum pump, slowly apply 5-10 in. Hg vacuum to EGR valve. When vacuum is fully applied, engine should do one or more of the following: Engine should stall. Idle speed should drop more than 100 RPM. Idle speed should return to normal when vacuum is released. Service or replace EGR valve if engine does not stall or idle speed does not respond as specified. Reconnect IAC harness connector. Unplug and reconnect vacuum hose at EGR valve.
EGR Vacuum Regulator Solenoid
Turn ignition off. Disconnect EGR Vacuum Regulator (EVR) solenoid wiring harness connector. Measure resistance across EVR solenoid terminals. If resistance is not 26-40 ohms, replace EVR solenoid.
TEST 9
For EGR function testing, see appropriate ENGINE PERFORMANCE section of electronic information product.