Part 1 of 3
EGR Testing Part 1 Of 3:
EGR Wiring Diagram:
CIRCUIT DESCRIPTION:
The ECM operates a vacuum solenoid to control the EGR valve. The solenoid is normally closed. The ECM provides a ground path to energize the solenoid. This allows vacuum to flow to the EGR valve.
The ECM monitors EGR effectiveness by de-energizing the EGR control solenoid thereby shutting off vacuum to the EGR valve diaphragm.
With the EGR valve closed, manifold vacuum will be greater than it was during normal operation and this will be relayed to the ECM by the map sensor. If the change is not within the calibrated window a Code 32 will set.
The ECM control of the EGR valve is based on the following inputs;
^ Vehicle speed is above 50 mph.
^ Manifold pressure is between about 60-70 kPa (BARO 100 kPa) at low altitudes or through 30-40 kPa (70 kPa BARO) at the higher altitudes.
^ TPS is between 9% and 20%.
^ No more than 0.4% change in the TPS while the test is being run.
TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.
1. Intake Passage: Shut "OFF" the engine and remove the EGR valve from the manifold. Plug the exhaust side hole with a shop towel or suitable stopper. Leaving the intake hole open, attempt to start the engine. If the engine runs at a very high idle speed (up to 3000 rpm is possible) or starts and stalls, the EGR passages are not restricted. If the engine starts and idles normal, the EGR intake side passage, in the intake manifold, is restricted.
Exhaust Passage: With the EGR valve still removed, plug the intake side hole with the same stopper. With the exhaust side hole open, check for the presence of exhaust gas. If no exhaust gas is present, the EGR exhaust side passage, in the intake manifold, is restricted.
NOTE: Remove towel or stopper once test is complete.
2. Grounding the diagnostic test terminal should allow the EGR solenoid to energize, and vacuum should flow to the gauge. The vacuum at the gauge may or may not bleed off slowly.
It is important that the gage is able to read the amount of vacuum being applied.
3. When the diagnostic test terminal is not grounded, the vacuum gauge should bleed off through a vent in the EGR solenoid. The vacuum gauge may or may not bleed off, but this does not indicate a problem.
4. This test determines if the electrical control portion of the system is at fault, or if the EGR solenoid and/or connector is at fault.
5. EGR valves used with this engine are stamped "P" for Positive and "N" for Negative. See EMISSION CONTROLS, for "EGR IDENTIFICATION," under COMPONENT OPERATION, to assist in determining the type of EGR valve used.
DIAGNOSTIC AIDS:
^ Vacuum hoses should be thoroughly inspected for proper routing.