How to: EGR System O&T

The purpose of this thread is to explain the operation and testing of the EGR system utilized in the generation II Explorers. In the past the EGR system has always been a mystery to me. Since I never was aware of any EGR malfunctions with any of my vehicles, I never bothered to learn how the system was designed to operate. I purchased my 2000 Sport in May 2009 and since then have noticed many EGR system problem related posts on this forum. I assume that with over 150,000 miles on the odometer, it will not be long before I will also experience EGR system problems. I decided to research the system now in preparation for an inevitable malfunction.

The following is from the Ford 2000 MY OBD System Operation Summary:

"Note: EGR normally has large amounts of water vapor that are the result of the engine combustion process. During cold ambient temperatures, under some circumstances, water vapor can freeze in the DPFE sensor, hoses, as well as other components in the EGR system. In order to prevent MIL illumination for temporary freezing, the following logic is used:

If an EGR system malfunction is detected above 32 oF, the EGR system and the EGR monitor is disabled for the current driving cycle. A DTC is stored and the MIL is illuminated if the malfunction has been detected on two consecutive driving cycles.

If an EGR system malfunction is detected below 32 oF, only the EGR system is disabled for the current driving cycle. A DTC is not stored and the I/M readiness status for the EGR monitor will not change. The EGR monitor, however, will continue to operate. If the EGR monitor determined that the malfunction is no longer present (i.e., the ice melts), the EGR system will be enabled and normal system operation will be restored."

The EGR system incorporates three different flow mediums: (1) exhaust gas, (2) vacuum pressure, and (3) electrical current. A significant deviation from norm in any of the flows results in a system malfunction. The OBD attempts to determine proper operation of the EGR system. The PCM is an automotive application specific computer that controls the operation of the engine and transmission. The PCM also executes the software associated with OBD. When the PCM detects a malfunction an associated DTC is stored in the PCM. If the same malfunction is detected on two successive drive cycles the CEL or sometimes called the MIL is illuminated. The PCM has a limited monitoring capability of the EGR system components and consequently can make erroneous determinations of the cause of a detected problem.

The structure of this thread will follow my perceived order of failure probability from highest to lowest. Consequently, following the testing order of the thread should statistically result in the quickest isolation of the failed component. Doing so should also reduce the instances of unnecessary replacement of functional components.

It is my opinion that due to high temperatures and particle content the exhaust gas flow is the most prone to failure. In addition, some of the components involved in the exhaust gas flow rely on mechanical movement that is subject to physical fatigue.

The next least reliable flow medium is the vacuum pressure. While the temperature and particle content occurring in the vacuum is much less than in the exhaust gas, so is the reliability of the flow duct. Vacuum hoses become brittle over time from engine heat and can eventually crack and leak due to continuous vibration. Also, some of the components involved in the vacuum pressure flow rely on mechanical movement.

The most reliable flow medium is the electrical current. The electrical components are designed to operate in temperature extremes that exceed those encountered in the engine compartment. The components are designed to operate properly when encountering shock and vibration extremes that are unlikely to occur. The most likely cause of malfunction is corrosion or physical damage to electrical connectors or shorting or breaking of wires.

You may notice that a specific DTC may be associated with multiple flow paths. An EGR system component such as the EGR valve involves more than one flow (i.e. exhaust and vacuum) directly and electrical current indirectly since it is controlled by the EGR valve regulator which is controlled by the PCM. There is inadequate instrumentation in the EGR system for the PCM to isolate a failure to a single component. That is why it is important to follow an organized test process to avoid unnecessary replacements.

Acronyms
CEL: check engine light
DTC: diagnostic trouble code
EGR: exhaust gas recirculation
MIL: malfunction indicator light
OBD: on-board diagnostics
PCM: powertrain control module

Related corrections and comments subsequently posted (encouraged) by members will be incorporated into the basic posts as deemed appropriate.

EGR System exhaust gas flow O&T

Associated DTCs:
P0401 Exhaust Gas Recirculation Flow Insufficient Detected
P0402 Exhaust Gas Recirculation Flow Excessive Detected
P1400 Differential Pressure Feedback Electronic Sensor circuit Low Voltage
P1401 Differential Pressure Feedback Electronic Sensor circuit High Voltage
P1405 Differential Pressure Feedback Electronic Sensor circuit Upstream Hose
P1406 Differential Pressure Feedback Electronic Sensor circuit Downstream Hose
P1408 EGR Flow out of Self-Test Range

Operation

The exhaust gas flow path starts at the EGR outlet port on the driver side exhaust manifold (shown below) and progresses to the EGR valve via the EGR pipe as shown below.


Located in the EGR pipe is an orifice (flow restriction) with small ports located slightly upstream and downstream. Each small port is connected to a metal tube that transitions to a high temperature flexible hose (as shown below) that connects to a port on the DPFE sensor.

The DPFE sensor (shown below) compares the static pressures of the exhaust gas before and after the orifice.

There is no actual exhaust gas flow toward the sensor unless there is a break in one of the metal tubes or flexible hoses. If the EGR valve is fully closed there will be no flow thru the orifice and the DPFE will detect equal static pressures from both inlets. When the EGR valve is open unmetered (not measured by the MAF sensor) exhaust gas is allowed to flow into the upper intake manifold and mix with the metered air for combustion in the cylinders. The more the EGR valve opens the greater the difference in static pressure across the orifice that is detected by the DPFE.

Acronyms
DPFE: differential pressure feedback EGR
DTC: diagnostic trouble code
EGR: exhaust gas recirculation
MAF: mass air flow

EGRS exhaust gas flow O&T (cont)

Testing

The first thing to test is the EGR valve. This is easily accomplished with a manual vacuum pump and gauge. With the engine Off disconnect and cap or plug the vacuum line attached to the top of the valve and attach a hose connected to a manual vacuum pump and gauge as shown below.

Apply 5 to 6 in-Hg to the valve and see if it holds the vacuum. If it doesn’t the diaphragm is ruptured and the valve must be replaced. If it holds vacuum then you must determine if the valve is opening. Release the vacuum and start the engine. With the engine idling gradually increase the vacuum and note if the idle becomes unsteady. You should notice an impact to the idle between 1 to 2 in-Hg. If the idle does not become irregular by the time the vacuum increases to 6 in-Hg then there is insufficient flow of exhaust gas into the intake manifold. Turn off the engine and inspect the EGR tube from the exhaust manifold to the intake manifold looking for a crimp restricting the flow. Then remove the EGR valve and inspect its inlet and outlet ports. Clean any dirty or blocked port, install the valve and repeat the idle test. If the test still fails replace the EGR valve.

The known good EGR valve can now be used in testing the DPFE sensor. Two different types of DPFE sensors with different electrical characteristics are utilized. One type has a black plastic housing and the other type has an aluminum housing. Backprobe the DPFE sensor signal (brown/light green wire) and the common sensor return (gray/red wire) and connect the backprobes to a voltmeter. Release the hand pump vacuum to the EGR valve (closes the valve), turn on the ignition and note the voltage which should be greater than 0.195 volts. Then start the engine. With the EGR valve closed there is no exhaust gas flow thru the orifice and the DPFE sensor output will be minimal. Note the reading and then subtract the value noted before the engine was started. The difference should be less than or equal to 0.6 volts. Using the hand pump gradually increase the vacuum while monitoring the DPFE sensor signal voltage. The voltage should increase to at least 4.0 volts but less than 4.96 volts as the vacuum increases to 6 in-Hg. If either voltage test fails it may be due to a poor electrical connection. Try cleaning the electrical contacts by disconnecting and reconnecting a couple times. It could also be due to an incorrect reference voltage. Backprobe the reference voltage pin (brown/white wire) and measure the voltage between it and the common sensor return. It should be at least 4.0 volts with the ignition on. If the test(s) still fail it may be due to moisture or carbon accumulation in the DPFE sensor inlet ports or connecting hoses. The high temperature insulation around the EGR tube and the DPFE connecting tubes increases heat retention and reduces moisture condensation. Even though the hoses are rated for high temperature they become brittle with age. Since they are also short in length, bending them for removal risks damaging them. A safer method is to disconnect the DPFE sensor electrical connector and then remove the mounting bolts. Then remove the DPFE sensor and hoses as an assembly. Work the hoses loose from the EGR pipe by carefully twisting and pulling. Once the assembly is loose remove each hose and inspect/clean the hoses and sensor ports. After cleaning reinstall and retest. If the test(s) still fail, replace the DPFE sensor.

Here are additional photos related to the EGR System exhaust gas flow operation and testing.

A closeup of the EGR valve is shown below.

If there's a possibility you may have to remove this valve, spray the threaded section with rust solvent the day before.

The photo below shows the EGR tube entering the upper intake manifold.


The photo below was taken after the throttle body was removed.

It shows the end of the EGR tube with holes to allow the exhaust gas to be mixed with the air flowing from the throttle body outlet port.

Acronyms
DPFE: differential pressure feedback EGR
EGR: exhaust gas recirculation

EGR System vacuum pressure flow O&T

Associated DTCs:
P0401 Exhaust Gas Recirculation Flow Insufficient Detected
P0402 Exhaust Gas Recirculation Flow Excessive Detected

Operation

First it should be explained that during normal EGR system operation there is no flow of air in the vacuum path. Unless there are leaks, the EGR vacuum system is closed except for the amount of air added or subtracted to vary the absolute static pressure according to the system control. A vacuum source hose identified by the red arrow in the photo below (upper and lower intake manifolds removed) connects to a port in the upper intake manifold.

The green arrows identify the routing of the vacuum source hose to the EVR connector identified by the blue arrow. The EVR inlet and outlet ports are identified with arrows in the photo of the EVR shown below.

The green arrow identifies the inlet that connects to the vacuum source. The red arrow identifies the outlet. The PCM controls the opening and closing of the EVR. The corresponding change in static pressure leaves the EVR outlet port and propagates to the EGR valve via a semi-rigid hose. The red arrows in the photo below indicate the routing of the vacuum hose between the EVR and the EGR valve.


Testing

Make sure that the EGR vacuum source hose is firmly connected to the intake manifold port. Visually follow the hose to the EVR checking for kinks or breaks. Then follow the hose connected to the other EVR port to the EGR valve again looking for kinks or breaks. Make sure the vacuum hose is firmly connected to the top of the EGR valve. Disconnect the electrical connector at the EVR and measure the resistance between the two contacts on the EVR. The resistance should be 20 to 70 ohms. The EVR is a fast acting electromagnetic solenoid that operates from 12 volts provided by fuse 13 (15 amps) in the battery junction box. Reconnect the electrical connector to the EVR and backprobe the 12 volt source pin (light blue/orange wire). Turn the ignition on and measure the voltage between the probe and ground. It should be battery voltage. Turn the ignition off, remove the backprobe, and backprobe the return line pin (brown/pink wire). This wire goes to the PCM that activates the EVR by grounding the line. Start the engine and let the idle stabilize. During normal operation there is no EGR at idle. Briefly ground the probe to energize the EVR solenoid. The idle speed should immediately become unsteady. Unground the probe and the idle should become steady. Turn off the ignition and remove the probe. Clear any set DTCs with an OBD device or by disconnecting the battery for 10 minutes and test drive the vehicle.

Acronyms
DTC: diagnostic trouble code
EGR: exhaust gas recirculation
EVR: EGR vacuum regulator
PCM: powertrain control module

EGRS vacuum flow O&T (cont)

The photo below is of the right rear of a 1996 V8 intake manifold directly below the PCM connector. The EGR vacuum regulator (EVR) is identified with the red arrow. To the right and below the EVR is the EGR valve identified with the green arrow.

The photo below is of the EGR valve.

EGRS electrical current flow O&T (cont)

EGR System electrical current flow O&T

Associated DTCs:
P0401 Exhaust Gas Recirculation Flow Insufficient Detected
P0402 Exhaust Gas Recirculation Flow Excessive Detected
P1400 Differential Pressure Feedback Electronic Sensor circuit Low Voltage
P1401 Differential Pressure Feedback Electronic Sensor circuit High Voltage
P1405 Differential Pressure Feedback Electronic Sensor circuit Upstream Hose
P1406 Differential Pressure Feedback Electronic Sensor circuit Downstream Hose
P1408 EGR Flow out of Self-Test Range
P1409 EGR Vacuum Regulator circuit malfunction/Electronic Vacuum Regulator Control circuit fault

Operation

Power is supplied to the EGR vacuum regulator from the Battery Junction Box. The PCM controls the solenoid in the EVR with alternating shorts and opens to generate a rectangular waveform (on/off) electrical current that flows thru the EVR. The duty cycle (time on vs time off) of the waveform is transduced to a corresponding opening and closing of the vacuum valve in the EVR.

An electrical current that corresponds to the static pressure difference in the exhaust before and after the orifice is output by the DPFE and routed to the PCM where it is sensed as a voltage.

EVR Testing

Check fuse 13 (15 amps) in the battery junction box. Disconnect the EVR electrical connector and connect the positive probe of a voltmeter to the light blue/orange wire or pin. Connect the negative probe of the voltmeter to ground. Turn the ignition switch to On and check the meter for battery voltage. Turn the ignition switch off. Disconnect the probe from the light blue/orange wire and reconnect the EVR electrical connector.

DPFE Testing

Disconnect the DPFE electrical connector and connect the positive probe of a multimeter to the brown/white wire or pin. Connect the negative probe of the multimeter to the gray/red wire or pin. Turn the ignition switch to On and check the meter for 4.0 to 6.0 volts. Turn the ignition switch off. Disconnect the meter probe from the brown/white wire of the DPFE and connect the probe to the gray/red wire connected to the TPS. Set the multimeter to ohms and check for less than 1.0 ohm. Remove the meter probes and reconnect the DPFE electrical connector.

Acronyms
DPFE: differential pressure feedback EGR
DTC: diagnostic trouble code
EGR: exhaust gas recirculation
EVR: EGR vacuum regulator
PCM: powertrain control module

additional egr data

The photo below shows the end of the EGR tube with the upper intake manifold removed.

The red arrow identifies the ring seal that prevents outside air from infiltrating the manifold.

Subscribing....

Hi,

Looking at the picture of the 1996 v8 intake manifold, there seems to be an electrical connector directly on top of the EGR valve. Is that correct? Is this another mechanical part?

no electrical connector to EGR valve

There is no electrical connector to the EGR valve. The electrical connector that is shown in the photo is to the EGR vacuum regulator (EVR) identified by the red arrow in the photo.

Hi

There is something mounted on top of the EGR valve on the 1996 v8 EGR valve. Also the picture of the new EGR valve shows 3 studs for mounting something. What is that?

Evr

The EVR is mounted to the intake manifold above the EGR valve. The photo below shows an EGR Vacuum Regulator.

There is a vacuum hose that connects the EVR to the EGR valve. I believe the EGR valve is attached to the intake manifold on one side and the exhaust on the other side. The EGR valve controls the flow of exhaust to the intake manifold.

Let me try to be more clear. The valve is mounted on the manifold on the v8 and the other end faces the firewall. There is something bolted directly to the valve on the end that faces the firewall. In YOUR PICTURE it is there and is a bit lighter gray in color than the valve itself. What is that?

That would be the EGR solenoid I reckon. The 1996 and early 1997 v8 are the ONLY explorers with a egr solenoid. Yes it is an electro-mechanical component. There is also a egr position sensor in place of the DPFE in this type system.

No Egr flow is actually measured in the V8 internal egr system like there is with the external( DPFE) system, rather it merely assumes EGR flow is present by the state of the egr valve position. Make sense?

OK
DPFE
Differential Pressure Feedback EGR

From my experimenting and reading--
The DPFE sensor is merely that-a differential sensor-

there are 2 tubes on the egr tube going to it, in between each of these tube "nozzles" on the egr tube is an orifice--
it is a thick metal bushing with a small hole. this causes a pressure difference between the 2 "nozzles" when the exhaust gasses pulse through.
To satisfy the DPFE sensor-all that is needed is a differential between the 2 nozzles.
ok for illustration here is a home made EGR tube that was needed on the (RIP) Mounty. I had to lengthen and move it a bit but this will show some things



Try to ignore that it has an extra orifice because it was made from 2 egr tubes

this picture shows the internal orifice



More visual stimulation for you.

OK thanks Turdle

So I'm gonna assume that the device on top of the valve is a position sensor(logical location). A solenoid wouldn't make sense, what would be its function? The valve is already vacuum commanded by the EVR. BTW nice homemade tube you made there..

EGR Valve Position Sensor

Rock Auto calls it an EGR Valve Position Sensor as shown below.


It seems redundant to me. I guess it provides a way to independently determine the valve position to compare with the PFE reading. Apparently going to DPFE allowed elimination of the position sensor which was probably not reliable.

So I checked to see if I had one of those DPFE things and of course I do.
But the hose fitting toward the front of the engine had melted off and the hose was very hard and brittle, I'd say it's not the right kind of hose.

What would it have been doing with that one hose disconnected?

And what's it doing now the both hoses are disconnected?

It seems to be running ok.

burning up stuff

Those open hoses allow exhaust gas to exit thru them melting anything plastic near the flow. The original hoses are high temperature rated and should not be replaced with normal vacuum hoses. When the hoses are connected to the DPFE sensor there is no flow thru them - only pressure for the DPFE sensor to sense and provide the results to the PCM. The PCM has probably detected the failure and disabled EGR.