CA Smog Help - EGR

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

EGR System theory and testing

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.

The EVR regulates vacuum to the EGR valve to maintain the correct amount of vacuum. The solenoid coil should measure 20-70 Ohms resistance. The regulator has a vacuum feed on the bottom which draws from the intake manifold. The other vacuum line is regulated vacuum going to the EGR valve. One side of the EVR electrical circuit is +12 volts anytime the ignition switch is in the run position. The other side of the electrical circuit is the ground path and is controlled by the computer. The computer switches the ground on and off to control the regulator solenoid.



EGR test procedure courtesy of cjones

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 or see the EGR test jig drawing below. Connnect the test jig or to directly to manifold vacuum.

Do not connect the EGR test jig to the EVR (Electronic Vacuum Regulator).

apply 5in vacuum to the valve. Using the test jig, use your finger to vary the vacuum

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 EGR test jig to the hose coming off of the EGR Valve.
Use your finger to cap the open port on the vacuum tee.
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 the EVR has failed

EGR test jig


To test the computer and wiring to the computer, you can use a test light across the EVR wiring connectors and dump the codes. When you dump the codes, the computer does a self test that toggles every relay/actuator/solenoid on and off. When this happens, the test light will flicker. If the test light remains on the computer or the wiring is suspect.

To check the EVR to computer wiring, disconnect the EVR connector and connect one end of the Ohmmeter to the dark green wire EVR wiring. Remove the passenger side kick panel and use a 10 MM socket to remove the computer connector from the computer. Set the Ohmmeter to high range and connect the other ohmmeter lead to ground. You should see an infinite open circuit indication or a reading greater than 1 Meg Ohm. If you see less than 200 Ohms, the dark green wire has shorted to ground somewhere.

Late Model Restoration may still have 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

Well, thanks to jrichker you now know EVERYTHING there is to know about the EGR valve on your car!

Let me simplify: Okay, so the smog nazi put vacuum on the EGR and it didn't stall the engine: This means not enough is flowing, which simply means it is probably clogged or partly clogged. This can be a mofo on a 5.0HO because the way the gasses flow.

Remove the EGR valve and see the passages both in the EGR valve and the manifold/tb spacer. Tape up the manifold with a piece of duct tape, one piece on each hole. Start the car. Remove the intake side and see if you are getting vacuum, it should suck pretty hard, probably stall the engine. If so, your good there. Remove the exhaust side and you should have a decent amount of exhaust gas coming through. If you do, your good there, if not, you have clogged exhaust ports.

Cleaning the intake side, the worse case you will have to remove the spacer and scrub it out. The exhaust side, not that one could suck, because if you are not lucky enough that the clogging is just in the EGR spacer, you're going to most likely have to pull the manifold off and clean it out with a bore brush and lots of carb cleaner. The EGR gets its gasses all the way from the head. I doubt it's clogged there, and you can from there probably clear it out with chemicals. Use compressed air to see if you have flow. If you do, you should be good.

I live in cali and you don't have to print out ****, nor go to a referree.....if a smog tech tells you that crap, move on to the next one.

I agree, the passages are probably clogged. The port in the head and bottom of the intake is pretty large, so like mentioned, start at the top where the egr mounts...the problem is prob around that area.

Some of the intake gaskets block off the EGR passages, others have two extra pieces that can be used for the same thing. It is possible that this may be the source of your problem if the manifold has the EGR passages in it.

Yeah with it removed and vacuum applied do you see the pintle moving? Mine held vacuum, and collapsed the diaphragm but it did not move the pintle. I actually soaked it in cleaner, and tapped it with a hammer then it worked like new again not getting stuck.

I just replaced mine today, mine would not hold any vacuum at any time. I think cats are going bad too. has anyone replaced theirs with the generic MagnaFlow Catalytic Converters?

If you are referring to the stock replacement unit available then yeah, it works wonders, but I have not used the individual replacement cats myself. I am using a good used one. I have a spare if you need and are in the area.

The guy who helped me diag the problem said that he thinks replacing the precats will solve the problem, the guy at the muufler shop who quoted $230 per cat plus $30 to install said replacing the backs will solve the problem

Here is what I am looking

http://www.oreillyauto.com/site/c/d...=Search_02404_1134065_3065&pt=02404&ppt=C0022

how about this, does any one make a system that is California legal from the shorty pipe back?

MagnaFlow 37338 - Catalytic Converter | O'Reilly Auto Parts

That is the perfect one

actually I think i am going with this

Amazon.com: Magnaflow 37338 Direct Fit Catalytic Converter - CARB Compliant: Automotive

Now I have figure out that muffler setup for the back

Haha, its the same one! But its cheaper from Oreilly's if your in CA.

Or if your close to Six Flags, I have a set that is guaranteed to work!

do you have this cat setup there?

I have an OEM 4 cat H-pipe.

TenorPlayinGuy said:

Yeah with it removed and vacuum applied do you see the pintle moving? Mine held vacuum, and collapsed the diaphragm but it did not move the pintle. I actually soaked it in cleaner, and tapped it with a hammer then it worked like new again not getting stuck.

Click to expand...

I'll have to ad the hammer trick to my EGR writeup...