Here's some EGR information a buddy sent me. He works at Ford in Dearborn.
1995 PCED OBD I A SECTION 10A: Exhaust Gas Recirculation (EGR) Systems
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EGR System Descriptions
Vacuum Operated EGR Systems
The Exhaust Gas Recirculation (EGR) System is designed to reintroduce exhaust gas into the combustion cycle lowering combustion temperatures and reducing the formation of Oxides of Nitrogen (NOx).
There are two basic types of EGR systems:
The Pressure Feedback Electronic (PFE)/Differential Pressure Feedback Electronic (DPFE) System (9J460 + 9D475)
The EGR Valve Position (EVP) System 9F483 (9H473 + 9G428)
The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration and is controlled by factors such as engine speed, engine vacuum, exhaust system back pressure, coolant temperature and throttle angle. All EGR valves are vacuum actuated. The vacuum diagram is shown on the emission decal for each calibration.
Pressure Feedback Electronic EGR (PFE/DPFE) Systems
PFE is a subsonic closed loop EGR system that controls EGR flow rate by monitoring the pressure drop across a remotely located sharp-edged orifice. The system uses a pressure transducer as the feedback device and controlled pressure is varied by valve modulation using vacuum output of the EGR Electronic Vacuum Regulator (EVR) solenoid (9J459). With a PFE system (Figure 1) , the EGR valve serves only as a pressure regulator rather than a flow metering device. The Differential Pressure Feedback Electronic EGR (DPFE) system (Figure 2) operates in the same manner except it directly monitors the pressure drop across the metering orifice. This allows for a more accurate assessment of EGR flow requirements.
Figure 1: Typical Pressure Feedback Electronic EGR (PFE) System
Figure 2: Differential Pressure Feedback Electronic EGR (DPFE) System
System Components
PFE EGR Valve
The PFE EGR valve (9D460) (Figure 3) is a conventional ported EGR valve. The service replacement for this valve is 9D475 which does not include the pickup tube/plug. The original pickup tube/plug should be used with the new service valve (9D475).
Figure 3: Typical PFE EGR Valve
PFE and DPFE Sensors
The Pressure Feedback Electronic EGR (PFE) and Differential Pressure Feedback Electronic EGR (DPFE) sensors (9J460) (Figures 4 and 5) convert a varying exhaust pressure signal into a proportional analog voltage which is digitized by the Powertrain Control Module (PCM). The PCM uses the signal received from the PFE or DPFE sensor to compute the optimum EGR flow.
Figure 4: Pressure Feedback Electronic EGR (PFE) Sensor
Figure 5: Differential Pressure Feedback Electronic EGR (DPFE) Sensor
EGR Valve Position (EVP) System
The EVP EGR Valve (Figure 6) is required in EEC systems where EGR flow is controlled by the Powertrain Control Module (PCM) through an EGR Valve Position (EVP) sensor attached to the valve.
The valve is operated by a vacuum signal from the EGR Electronic Vacuum Regulator (EVR) Solenoid (9J459) which actuates the valve diaphragm.
As supply vacuum overcomes the spring load, the diaphragm is actuated. This lifts the pintle off its seat allowing exhaust gas to recirculate (flow). The amount of flow is proportional to the pintle position. The EVP sensor mounted on the valve sends an electrical signal of its position to the PCM.
Figure 6: Typical EGR Valve Position (EVP) System
System Components
EVP EGR Valve
The EGR valve (Figures 7 and for this system is a vacuum operated EGR valve which maintains a sonic flow in the valve seat/pintle area.
The EVP EGR valve assembly (9F483) is not serviceable. The EVP sensor (9G428) and EGR valve (9H473) must be serviced separately.
Figure 7: EVP EGR Valve—5.0L Mustang and 5.8L Truck (Lightning)
Figure 8: EVP EGR Valve—All Other Applications
EGR Valve Position (EVP) Sensor
The EVP sensor (9G428) (Figure 9) provides the EEC system with a signal indicating position of the EGR valve.
Figure 9: EGR Valve Position (EVP) Sensor
EGR Electronic Vacuum Regulator (EVR) Solenoid
The EGR Electronic Vacuum Regulator (EVR) solenoid (9J459) (Figure 10) is an electromagnetic device which controls vacuum output to the EGR valve. An electric current in the coil induces a magnetic field in the armature which pulls on a disk closing the vent to atmosphere. The Powertrain Control Module (PCM) outputs a duty cycle to the EVR which regulates the vacuum level to the EGR valve. As the duty cycle is increased, so is the vacuum signal to the EGR valve. The vacuum source is manifold vacuum.
Figure 10: EGR Electronic Vacuum Regulator (EVR) Solenoid
Vacuum Reservoir
The Vacuum Reservoir (9E453) (Figure 11) stores vacuum and provides "muscle" vacuum. It prevents rapid fluctuations or sudden drops in a vacuum signal such as those seen during an acceleration period.
Figure 11: Vacuum Reservoirs
Diagnosis
When charged initially with 51-67 kPa (15-20 in-Hg) vacuum, vacuum loss shall not exceed 2 kPa (.5 in-Hg) in 60 seconds. If it does, replace the reservoir.
Vacuum Check Valve
A vacuum check valve (12A197) (Figure 12) blocks airflow in one direction and frees airflow in the other direction. The check side of this valve will hold the highest vacuum seen on the vacuum side. If not, replace it.
Figure 12: Vacuum Check Valve
Diagnosis
Apply 54 kPa (16 in-Hg) vacuum to "check" side of valve and trap. If vacuum remains above 50.6 kPa (15 in-Hg) for 10 seconds, the valve is acceptable.
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1995 PCED OBD I A SECTION 10A: Exhaust Gas Recirculation (EGR) Systems
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EGR System Diagnosis By Symptom
Condition Possible Source Action
Rough Idle Cold
EGR valve malfunction.
RUN Quick Test.
EGR flange gasket leaking.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
EGR valve attaching nuts or bolts loose or missing.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specif ication.
Vacuum leak at EVP sensor.
REPLACE O-ring seal and TIGHTEN EVP sensor attaching nuts to specification.
EVR solenoid malfunction.
RUN Quick Test.
EGR valve contamination.
CLEAN EGR valve.
Rough Idle Hot
EGR valve malfunction.
RUN Quick Test.
EGR flange gasket leaking.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
EGR valve attaching nuts or bolts loose or missing.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
Vacuum leak at EVP sensor.
REPLACE O-ring seal and TIGHTEN EVP sensor attaching nuts to specification.
EVR solenoid malfunction.
RUN Quick Test.
EGR valve contamination.
CLEAN EGR valve.
Rough Running, Surge, Hesitation, Poor Part Throttle Performance—Hot
EGR valve malfunction/erratic operation.
PERFORM EGR valve functional diagnosis.
EGR valve contamination.
CLEAN EGR valve and if necessary, replace EGR valve.
EVR solenoid malfunction.
RUN Quick Test.
Pressure/Vacuum signal hose(s) leak (PFE/DPFE).
REPLACE hose(s).
Engine Stalls On Deceleration—Hot
EGR valve malfunction.
PERFORM EGR valve functional diagnosis.
EVR solenoid malfunction.
RUN Quick Test.
EGR valve contamination.
CLEAN EGR valve and if necessary, replace EGR valve.
Engine Spark Knock or Ping
EGR valve malfunction.
PERFORM EGR valve functional diagnosis.
EGR valve attaching nuts or bolts loose or missing.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
Blocked or restricted passages in valve or spacer (EVP).
CLEAN passages in EGR spacer and EGR valve.
Engine Stalls At Idle—Cold
EGR valve malfunction.
PERFORM EGR valve functional diagnosis.
EGR flange gasket leaking.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
EGR valve attaching nuts or bolts loose or missing.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
EVR solenoid malfunction.
RUN Quick Test.
EGR valve contamination.
CLEAN EGR valve.
Engine Stalls At Idle—Hot
EGR valve malfunction.
PERFORM EGR valve functional diagnosis.
EGR flange gasket leaking.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
EGR valve attaching nuts or bolts loose or missing.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
EGR valve contamination.
CLEAN EGR valve and if necessary, replace EGR valve.
Vacuum leak at EVP sensor.
REPLACE O-ring seal and TIGHTEN EVP sensor attaching nuts to specification.
EVR solenoid malfunction.
RUN Quick Test.
Engine Starts But Will Not Run—Engine Hard To Start Or Will Not Start
EGR valve malfunction.
PERFORM EGR valve functional diagnosis.
EGR flange gasket leaking.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
EGR valve attaching nuts or bolts loose or missing.
REPLACE flange gasket and TIGHTEN valve attaching nuts or bolts to specification.
EVR solenoid malfunction.
RUN Quick Test.
EGR valve contamination.
CLEAN EGR valve.
1995 PCED OBD I A SECTION 10A: Exhaust Gas Recirculation (EGR) Systems
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EGR: EGR System Functional Diagnosis
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EGR1 CHECK SYSTEM INTEGRITY
Check vacuum hoses and connections for looseness, pinching, leakage, splitting, blockage and proper routing.
Inspect EGR valve for loose attaching bolts or damaged flange gasket.
Does system appear to be in good condition and vacuum hoses properly routed?
Yes No
GO to EGR2 . SERVICE EGR system as required. RE-EVALUATE symptom.
EGR2 CHECK EGR VACUUM AT IDLE
Run engine until normal operating temperature is reached.
With engine running at idle, disconnect EGR vacuum supply at the EGR valve and check for a vacuum signal.
Note: The EVR solenoid has a constant internal leak. You may notice a small vacuum signal. This signal should be less than 3.4 kPa (1.0 in-Hg) at idle.
Is EGR vacuum signal less than 3.4 kPa (1.0 in-Hg) at idle?
Yes No
GO to EGR3 . RECONNECT EGR vacuum hose. INSPECT EVR solenoid for leakage. RUN Quick Test.
EGR3 CHECK EGR VALVE FUNCTION
Install a tachometer, Rotunda 059-00010 or equivalent.
Disconnect the Idle Air Control (IAC) solenoid (9F715) electrical connector.
Remove and plug the vacuum supply hose from the EGR valve nipple.
Start engine, idle with transmission in NEUTRAL, and observe idle speed. If necessary, adjust idle speed according to Section 12A.
Note: If the engine will not idle with IAC solenoid disconnected, provide an air bypass to the engine by slightly opening the throttle plate or by creating an intake vacuum leak. Do not exceed a typical idle rpm.
Slowly apply 5-10 inches of vacuum to the EGR valve nipple using a hand vacuum pump, Rotunda 021-00014 or equivalent.
Does idle speed drop more than 100 rpm with vacuum applied and return to normal (± 25 rpm) after the vacuum is removed?
Yes No
The EGR valve is OK. UNPLUG and RECONNECT the EGR valve vacuum supply hose. RECONNECT the IAC solenoid connector. REFER to Diagnostic Routines, Section 2A. INSPECT the EGR valve for blockage or contamination. CLEAN the valve using Rotunda 021-80056 EGR valve cleaner. INSPECT valve for vacuum leakage. REPLACE if necessary. If EGR valve is OK, inspect the EGR flow path in the intake manifold for blockage.
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Rotunda Equipment Model Description
021-00014 Vacuum Pump
021-80056 EGR Valve Cleaner
059-00010 Tachometer
I laughed and said I'd just grab an X pipe for $500 from a local shop and improve the sound and performance. And that's what I did. 
Time to go check the weather. 
