smoke test for vacuum leak?

Yeah, that doesn't sound right to me at all.

The EGR should not leak smoke or vacuum in any shape or fashion.

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

I'm looking for some help and info sounds like a possible solution for my problem but the tech help seems a little over my head. My car starts and idles well after a few moments of running it will stutter under load but after about five minutes it will clear up and run good. The vacuum lines look ok but there are some vacuum lines from the pods that are blocked off. Any ideas. Sorry to thread jack but im curious if the egr could be causing my problems. Thanks

187mustang said:

I'm looking for some help and info sounds like a possible solution for my problem but the tech help seems a little over my head. My car starts and idles well after a few moments of running it will stutter under load but after about five minutes it will clear up and run good. The vacuum lines look ok but there are some vacuum lines from the pods that are blocked off. Any ideas. Sorry to thread jack but im curious if the egr could be causing my problems. Thanks

Click to expand...

Attach your problem to the end of the "Surging Idle Checklist and I will try to help.

See the "Surging Idle Checklist for help with all your idle/stall problems.

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

Buddy said:

Well, I'm at a dead end. I've installed and tested 4 different EGR valves with the smoke machine. (2 used, 1 new from Rockauto "Standard", 1 new Motorcraft from Rockauto) All 4 leak smoke out of the holes in the EGR housing. I don't understand why they're leaking - could all 4 be faulty?

I also mocked up an EGR blockoff plate and installed it. The symptoms seemed less severe, but still present.

Symptoms are as stated in my initial post: when cold, good idle, good acceleration. After about 3 minutes, backfires/hesitates on partial acceleration. Wide open, it's strong - no hesitation.

I'm back to square 1. Suggestions, anyone?

Thanks.

Buddy

Click to expand...

Have you dumped the codes and done the EGR test that I posted?

I JUST WENT THROUGH THIS!!! I pressurized the engine w/everything blocked off. What I found was the EGR valve leaking and it seemed pretty bad. Got another one off a car that idles fine, and it didn't really change anything regarding my vacuum readings only a hair ... so I thought why buy a new one! The problem I found was that the EGR valve has basically 2 ports. The one with the pintle is tapered (self-cleaning) and was sealed. However, the exhaust gas are pushing/pulling thru the open port and exiting via the diaphram rod and housing into the diaphram chamber which has a bunch of holes on the outside open to atmospheric pressure!!! Thus, when it opens, it can pull in outside air or create a leak. I didn't want to buy another since a new one probably has this small clearance for the diaphram rod to move back and forth (dunno) ... but, they do apparently leak! When blocked off completely, my vacuum reading did go up 1-2 in hg. I have no EGR codes whatsoever and never have but it definitely leaked here so much that it could be heard easily when the intake system was pressurized with 3-5 psi. So, like you, I wondered what the deal is? Is the valve bad cuz its leaking or is this acceptable? Would a new one leak the same amount? As I said, I grabbed one off another car that idled good (but it was used) but it did not change my rough idle when installed nor raised my vacuum reading. This is obviously a vacuum leak that the engine sees ... add it to the EVR vacuum bleed off and could this be creating a rough condition???

I have just about all of the same symptoms as you and have replaced just about all of the same things as you to no avail. I do seem to see some misses with my timing light hooked up to different wires but nothing consistent ... got me thinking it was a lean misfire or something. When first started and it elevates idle, it runs fairly smooth (richer mixture, I guess) ... but as it idles down, it gets real rough at idle especially cold ... as it warms up, it gets better somewhat if not left idling too long. On restarts (warm), it idles like crap. I did gain 1-2 in Hg. vacuum by blocking the EGR off but the EGR keeps it from pinging etc.. So, what is the answer here???