EGR ... To delete or not to delete?

There is no good reason to delete the EGR on a street driven daliy driver.

You may have already seen this, but here it is for review.

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.



This will affect idle quality by diluting the intake air charge

I deleted mine. And never had any running probablem with it. Most don't work anyways because all the carbon build up in the lines on back of the heads.

88mouse said:

I deleted mine. And never had any running probablem with it. Most don't work anyways because all the carbon build up in the lines on back of the heads.

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You are confusing the Thermactor Air System (smog pump) with the EGR. They are two different and totally separate systems.

I suggest you look closely at the post explaining how the EGR works. You won't find a line across the back of the heads in the diagram because it belongs to the Thermactor Air System.

oops. I deleted all my smog stuff. But my intake and the lines on back of the heads where stoped up with carbon.

Well mine didn't run lean, rich if anything. No surging. Started idleing better after i deleted it tho.

Isn't it true that if the EGR throws a code (like it is gone or not working) then it's function is disabled in the computer? In other words you don't need to get a chip or tune to turn it off.

I feel like EGR and Thermactor systems are the most misunderstood systems on this forum. People do not want to spend the time to read through and understand all the information in Jrichker's posts. I do not believe that when the EGR system is throwing a code, that it disables the entire system in the computer. What test did the code 34 come up in...was it KOER or KOEO?

i deleted my egr completely. i bought a connector bung from ebay for 20.00 and plugs into the egr connector. it tricks the computer in thinking the egr is functioning properly. i had no problems at all. shaped a piece of metal to cover the hole on the backsde of the intake. looks a lot cleaner.

so my opnion...........delete it!!!

myslo50 said:

i deleted my egr completely. i bought a connector bung from ebay for 20.00 and plugs into the egr connector. it tricks the computer in thinking the egr is functioning properly. i had no problems at all. shaped a piece of metal to cover the hole on the backsde of the intake. looks a lot cleaner.

so my opnion...........delete it!!!

Click to expand...

Why delete it? You gain absolutely nothing except a slightly cleaned up engine compartment.

that was the purpose if it, was to make the compartment cleaner