1986 Pulse-Width Modulated EGR Valve

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2.8L

The EGR valve is controlled by a normally closed solenoid (allows vacuum to pass when energized). The ECM energizes the solenoid to turn the EGR on and monitors vacuum to the EGR with the EGR diagnostic switch. Code 32 will detect a faulty solenoid, vacuum switch or vacuum supply.

NOTE: Test numbers refer to test numbers on diagnostic chart.

With the ignition on and engine stopped, the solenoid should not be energized and vacuum should not pass to the EGR valve.
Grounding the diagnostic terminal will energize the solenoid and allow vacuum to pass the valve.
Checks for plugged EGR passages. If passages are plugged, the engine may have severe detonation on acceleration.
The EGR solenoid will not be energized in Park or Neutral. This will determine if the Park/Neutral switch input is being received by the ECM.

5.0/5.7L

The EGR valve is controlled by a normally open pulse width modulated solenoid (PWM). The ECM turns the solenoid off to allow vacuum to pass to the EGR and turns the solenoid on to prohibit EGR operation. When EGR is commanded, the solenoid is turned on and off many times a second (duty cycle).

The duty cycle is calculated by the ECM based on information from the coolant, MAT, TIPS and MAF sensors. Also, engine RPM and the Park/Neutral switch inputs affect EGR. There is no EGR when in Park or Neutral and TPS is below a calibrated value or TPS is indicating wide open throttle (WOT). With the ignition on and engine stopped, the EGR solenoid is de-energized. The solenoid, however, should be energized if the diagnostic terminal is grounded with the ignition on and engine not running.

NOTE: Test numbers refer to test numbers on diagnostic chart.

This will test the solenoid value to determine if it is capable of closing off the manifold vacuum from the EGR valve. The vacuum may bleed off slowly but this should not be considered a fault.
As soon as back pressure is available at the EGR valve, the bleed portion in the valve should open and cause the valve to go to its heated position.
The EGR valve will be inoperative if the Park/Neutral switch is misadjusted or defective. Use "SCAN" tester and check Park/Neutral switch.

NOTE: Before using this chart, check for ported vacuum to EGR solenoid, also check hoses for leaks and restrictions. Should be at least 7" Hg vacuum at 2000 RPM. This chart assumes there is no Code 32.

Fig 1: Flow Chart C7B, EGR Recirculation Check (5.0/5.7L)