EGR Valve problems

Instead of throwing parts at it with no idea as to what's wrong, I would try figuring out what is causing the error code before buying anything else.

The EGR Valve is controlled by the EGR vacuum regulator, which is mounted on the back of the passenger side strut tower. It is a black valve with a gray top that has one two-wire electrical connector and two vacuum hoses attached two it. That regulator controls the position of the EGR valve via vacuum. The regulator gets vacuum from the intake manifold, and then regulates that vacuum to the EGR valve.

To start off with, I would check to make sure the entire length of both vacuum hoses (from the EGR valve to the regulator, and from the regulator to manifold vacuum source) are not cracked or broken.

Another possible, less likely problem would be with the electrical connector at the EGR vacuum regulator.

Make sure that you replaced the EGR valve gasket that mounts between the EGR valve and the EGR housing. It is a thick, metallic gaskets that many folks don't replace when replacing the valve because it usually stays in tact and feels solid enough to reuse. That is a no-no, EGR valve gaskets must be replaced every time the valve is removed, no matter how intact/solid it is.

Don't quote me but I believe that there are TWO solenoids that deal with and feed the EGR. the TAD and the TAB. Both are in the location that jt has indicated above.

I've discovered that doing voltage and resistance checks on these solenoids pretty much tells you NOTHING. They can test good and still not function.

Daggar said:

Don't quote me but I believe that there are TWO solenoids that deal with and feed the EGR. the TAD and the TAB. Both are in the location that jt has indicated above.

I've discovered that doing voltage and resistance checks on these solenoids pretty much tells you NOTHING. They can test good and still not function.

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Sorry Daggar, I am quoting you lol

The EGR Vacuum Solenoid is the only solenoid that controls the EGR Valve.

The TAB and TAD solenoids are mounted on a single metal bracket, and are both located BELOW the EGR vacuum solenoid on the same strut tower.

However, the TAB (Thermactor Air Bypass) and TAD (Thermactor Air Diverter) solenoids are part of the Thermactor AIR injection system, NOT the EGR system.

The TAB Solenoid controls the TAB valve just behind the smog pump, and the TAD solenoid controls the TAD valve, which controls the flow of air either to the rear of the cylinder heads, or down to the catalytic converters.

There ya go... I knew better than to rely on memory but figured someone would corect it if I got it WRONG. hehehe

Ensure your sensor and valve are in calibration. If they are not in synch and matched-up, you can spit the code.

Good luck.

Some basic theory to clarify how things work is in order…

The EGR shuts off at Wide Open Throttle (WOT), so it has minimal effect on performance. The addition of exhaust gas drops combustion temperature, increases gas mileage and reduces the tendency of the engine to ping. It can also reduce HC emissions by reducing fuel consumption. The primary result of EGR usage is a reduction in NOx emissions.

The EGR system has a vacuum source (line from the intake manifold) that goes to the EVR, computer operated electronic vacuum regulator. The EVR is located on the back of the passenger side shock strut tower. The computer uses RPM, Load. and some other factors to tell the EVR to pass vacuum to open the EGR valve. The EGR valve and the passages in the heads and intake manifold route exhaust gas to the EGR spacer (throttle body spacer). The EGR sensor tells the computer how far the EGR valve is open. Then computer adjusts the signal sent to the EVR to hold, increase or decrease the vacuum. The computer adds spark advance to compensate for the recirculated gases and the slower rate they burn at.




Troubleshooting:
There should be no vacuum at the EGR valve when at idle. If there is, the EVR (electronic vacuum regulator) mounted on the backside of the passenger side wheelwell is suspect. Check the vacuum line plumbing to make sure the previous owner didn’t cross the vacuum lines.

Diagram courtesy of Tmoss & Stang&2birds. (the diagram says 88 GT, but the EGR part is the same for 86-93 Mustangs)


The EGR sensor is basically a variable resistor, like the volume control on a radio. One end is 5 volt VREF power from the computer (red/orange wire). One end is computer signal ground (black/white), and the middle wire (brown/lt green) is the signal output from the EGR sensor. It is designed to always have some small voltage output from it anytime the ignition switch is the Run position. That way the computer knows the sensor & the wiring is OK. No voltage on computer pin 27 (brown/lt green wire) and the computer thinks the sensor is bad or the wire is broken and sets code 31. The voltage output can range from approximately .6-.85 volt.


EGR test procedure courtesy of cjones

to check the EGR valve:
bring the engine to normal temp.
connect a vacuum pump to the EGR Valve
apply 5in vacuum to the valve.
if engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.
if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.
if engine stumbled, connect vacuum gauge to the hose coming off of the EGR Valve
snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
did the vacuum gauge show about 2-5 in vacuum?

if not, check for manifold vacuum at the EGR vacuum valve.
if you have manifold vacuum then connect vacuum gauge to the EGR valve side of the vacuum valve and snap throttle to 2500 RPM.
should read about 2-5 in vacuum


Late Model Restoration has the Ford Racing M-12071-N302 kit with the EGR valve & sensor along with the ACT & ECT sensors for $45. See http://www.latemodelrestoration.com/iwwida.pvx?;item?item_no=M12071N302 1&comp=LRS for more details

Code 34 Or 334 - EGR voltage above closed limit - Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat. Remove the EGR valve and clean it with carbon remover. Prior to re-installing see if you can blow air through the flange side of the EGR by mouth. If it leaks, there is carbon stuck on the pintle valve seat, replace the EGR valve ($85-$95).

If the blow by test passes, and you have replaced the sensor, then you have electrical ground problems. Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1.5 ohm. Next check the resistance between the black/white wire and the negative battery post. It should be less than 1.5 ohm.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.

Let’s put on our Inspector Gadget propeller head beanies and think about how this works:
The EGR sensor is a variable resistor with ground on one leg and Vref (5 volts) on the other. Its’ resistance ranges from 4000 to 5500 Ohms measured between Vref & ground, depending on the sensor. The center connection of the variable resistor is the slider that moves in response to the amount of vacuum applied. The slider has some minimum value of resistance greater than 100 ohms so that the computer always sees a voltage present at its’ input. If the value was 0 ohms, there would be no voltage output. Then the computer would not be able to distinguish between a properly functioning sensor and one that had a broken wire or bad connection. The EGR I have in hand reads 700 Ohms between the slider (EPV) and ground (SIG RTN) at rest with no vacuum applied. The EGR valve or sensor may cause the voltage to be above closed limits due to the manufacturing tolerances that cause the EGR sensor to rest at a higher position than it should.

The following sensors are connected to the white 10 pin connector (salt & pepper engine harness connectors)


This will affect idle quality by diluting the intake air charge

chr1s11575stang said:

ok and how do you do this?

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Mustang5L5 said:

I guess i've been off in the 4.6L world too long...


that one made me just scratch my head

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The seat can wear, causing the sensor to read incorrectly for a given EGR position.
Check the sensor-return reading when the EGR is closed.
If there's an issue, it's often easier to modify the sensor than anything else.

Not very hard to delete the egr system either, I did with mine after a fresh rebuild cause I'd rather not crud up my new clean motor to save the environment (definitely not a choice if you live in a state with emissions laws)