1993 Ford Mustang Failing California Smog - Possible EGR Sy

Tiny
THEBAMES
  • MEMBER
  • 1993 FORD MUSTANG
  • V8
  • 2WD
  • MANUAL
  • 92,000 MILES
Let me give a little background first. I have a 1993 Mustang that I bought new. I put a lot of bolt-on performance parts on it during the first 5 years, all of which were CARB certified (intake manifold, u/d pullies, throttle body, mass air sensor, K&N conical, headers, exhaust). The car runs great, idles smooth, and the check engine light has never been on.

I have passed smog with flying colors until about 5 years ago, when I started barely scraping by. Well, I failed this most recent smog check. I knew that I had a bad cat at the time, and the test revealed that my timing was way too high, causing my NOx reading to be very high. It also failed HC. I fixed the timing, and got a new cat h-pipe. I took the car back in and it failed, although the numbers looked much better. This time it passed everything but the NOx at both speeds, which is sitting at about 1000 ppm, and should be somewhere around 750.

I read a lot of forums and articles on-line, and decided that cleaning the MAF sensor was a good idea (using MAF Sensor cleaner only), as well as Sea Foaming via vacuum system. I did both of these, and the car actually ran even better. I took it back for another smog test, and it passed everything but the NOx at 25mph. The 15 mph NOx dropped from 1000 to 650, which was amazing with only the SeaFoam and MAF sensor cleaning.

Now we are to the current day. I will be going back for another test in a couple weeks. DMV is getting impatient. I should probably take it in, but I'm determined to fix this myself. Of course everyone points to the EGR for high NOx. So I checked first to ensure the EGR valve was mechanically operational. I pulled of the vacuum line that goes to the EGR, and, with the engine idling, I applied a small amount of suction to the EGR valve, and the engine faultered, as it should if the EGR valve is opened at idle. My understanding is that the EGR is closed at idle and wide open. I also removed the EGR valve, cleaned it, and ensured it opens and closes freely. The diaphram looks great. No leaks. It can easily be opened with a little suction. Then I proceeded to check the other end, to make sure that vacuum was being applied when needed. So, per some internet help, I brought the car to operating temperature, I took off the line that connects to the EGR valve, blipped the throttle to 2500 rpm, and tested for vacuum from the EVR (EGR Vacuum Regulator) solenoid. Nothing. No vacuum. Next, I took off the EVR solenoid, and attempted to test it by applying some voltage to it, and then blowing through it to see if it opened. It didn't, but I wasn't confident I was testing it correctly. So I went out and bought a new EVR solenoid, installed it, and still no vacuum during the test. Unless this test is wrong, it seems that the EGR not getting vacuum is the reason I am failing smog. I'm just trying to figure out what tells that solenoid to open the vacuum line to the EGR valve. I'm sure it's the computer, but is another sensor telling the computer that it needs to open? I was also going to replace the EGR valve position sensor, for no apparent reason, other than the fact that it is a part of the EGR system, and might be faulty.

I have also ordered a couple new oxygen sensors, as mine have never been replaced. Note that my CO reading in all but the last smog check was 0, which, according to others, means that the car is running lean. The most recent smog check showed the CO was up a little, but not much, I tested for vacuum leaks, but none were found.

Although it seems unrelated, I have another question. My fuel pressure is running high, at about 55 psi. Per the manual, I believe it should be at 38-40 psi. Does this mean my regulator is shot?

Again, the car runs smooth and strong. It's just putting out too much smog!

So that's my dilemma. Sorry to be so verbose, but I know I will get a better answer if I give all of the information.

Thanks!
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Friday, October 10th, 2008 AT 5:49 PM

17 Replies

Tiny
RACEFAN966
  • EXPERT
Ok first the electric sensor on the top of the valve does not open it, that only tells the computer how far it is open and when. It opens on a combination of vacuum and backpressure. If the egr controller is not sending the vacuum signal to open then replace that first and get vacuum to the valve first. Let me know where this leads you ok.
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Saturday, October 11th, 2008 AT 10:52 AM
Tiny
THEBAMES
  • MEMBER
I believe is what you are referring to is the EVR (EGR Vacuum Regulator) solenoid. Per my original message, I already replaced this solenoid. Thanks
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Saturday, October 11th, 2008 AT 7:02 PM
Tiny
RACEFAN966
  • EXPERT
It is still conrolled buy vacuum and backpressure for the exaust. If you have little to no backpressure then it will not open either. The computer with the help of the throttle position sensor and the egr position sensor give the comand at when and how far to open. Hope this is more of what you were looking for. Let me know ok.
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Saturday, October 11th, 2008 AT 9:52 PM
Tiny
THEBAMES
  • MEMBER
Ok, so if I have already replaced the solenoid, what is the next step. Should I try replacing the TPS and EGR position sensor?
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Tuesday, October 14th, 2008 AT 11:25 AM
Tiny
RACEFAN966
  • EXPERT
No you should test them. Lets go with the TPS first ok. Find the green wire coming from it and back probe it (you need a digital volt meter) and then turn the key on engine off. With the throttle closed it should read.8 volts. Now slowly lift the throttle (engine still off) and it should slowly increase to 4.5 or 5 volts with no glitches inbetween. Let me know what you find here and we will go from there ok.
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Tuesday, October 14th, 2008 AT 8:30 PM
Tiny
THEBAMES
  • MEMBER
Ok, I did it. With the throttle closed, it was at exactly .8, and went smoothly up to 4.6 with it all the way open. So I guess the position sensor is next right? Thanks!
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Tuesday, October 14th, 2008 AT 10:19 PM
Tiny
RACEFAN966
  • EXPERT
Have we checked the knock sensor? If it is retarding the timing you get the same results it runs ok and all but it won't pass smog. I was a smog tech and vehicle inspector in Cali when I first got into this business after the Marines. It could also be that the exhaust is to free flowing and not causing enough backpressure to open the EGR valve. See the valve will not open in park or neutral it must be in gear and have some back pressure. Are they doing the smog on a dino? Get back to me we will get this thing figured out.
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Wednesday, October 15th, 2008 AT 9:56 AM
Tiny
THEBAMES
  • MEMBER
I have not tested the knock sensor, however, I was basing my assumptions about the psossible issue with the EGR system due to the lack of vacuum to the EGR valve. There are several forums out there where people explain both how to test the valve, and how to test the vacuum. See the test procedure below. Per 'cjones' (and many others), you can blip the throttle to 2500 rpm to get some vacuum (see procedure below). Note that there is a ton of vacuum going to the EVR solenoid, it's just not opening. And the valve itself tested out good.

So, if this method is not possible, how can one check if the EGR is ever opening? Is there a way to have it stay open without it dying at idle, just to pass smog?

They are doing the smog on the dino. They are acutally driving it. See my original question. It only fails at 25 mph, not 15 mph.

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

To test 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.
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Wednesday, October 15th, 2008 AT 10:48 AM
Tiny
RACEFAN966
  • EXPERT
Ok still is there enought back pressure from the exhaust. Secondly do you have power to the egr controller not the egr possition sensor but contoller.
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Wednesday, October 15th, 2008 AT 12:06 PM
Tiny
THEBAMES
  • MEMBER
Are you referring to the EVR (EGR Vacuum Regulator) solenoid? The one that I said I changed? Or is the controller something else? If you're referring to the solenoid that opens to let the vacuum through to the EGR valve, I have not checked to see it has power, but I can. How do I do this? I assume I test it at the harness, but is power only sent to it when it needs to open? Please send instructions on how to test it.

Thanks again for your help with this!
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Wednesday, October 15th, 2008 AT 4:22 PM
Tiny
RACEFAN966
  • EXPERT
Yes that is exactly what I am talking about. You will need to use a test light and bring it up to the 2000 rpm and do the same snap test as before and the light should come on.
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Wednesday, October 15th, 2008 AT 8:54 PM
Tiny
THEBAMES
  • MEMBER
Okay, sounds good. I just have a DMM and a household test light. I will buy an auto test light today. I'm sure it will be useful going forward. Assuming I'm not getting power to the solenoid when I blip the throttle, what would be the next step?
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Thursday, October 16th, 2008 AT 5:21 PM
Tiny
THEBAMES
  • MEMBER
I bought the test light. I tested it, and the light went on without having to rev the engine. Is this right? Doesn't it mean that the solenoid would be open all the time?
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Thursday, October 16th, 2008 AT 8:29 PM
Tiny
THEBAMES
  • MEMBER
Forget my last post. I was testing it with it ground to the shock tower, and not to the other terminal on the harness. I did the test again grounding to the other terminal, and the light comes on when I rev the engine to 2-2500 rpm. Sounds like the electronics are working. What's next?
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Friday, October 17th, 2008 AT 2:30 PM
Tiny
RACEFAN966
  • EXPERT
Sound like it is working as per what it should be doing. Wow this has got me stumped now I will do some checking at work on me mitchelle 1 and see if I can find a wiring diagram to be of more help. Now the exhaust port to the egr isn't pluged is it? Get back to ok
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Monday, October 20th, 2008 AT 6:29 PM
Tiny
THEBAMES
  • MEMBER
I had my smog test today, and I finally passed after 15 months!

So with your help, and help from another forum, here is what I did:

-Cleaned the MAF sensor
-Cleaned the throttle body
-Cleaned the EGR valve
-Tested the EGR valve - passed
-Tested the TPS - passed
-Tested the EVR - passed
-Sea Foam via vacuum system (which cut my NOx in half at 15 mph last test)
-Sea Foam through the fuel lines
-Sea Foam in the crank case for about 500 miles
-Installed new oxygen sensors (after Sea Foam treatments)
-Changed oil a couple days before test
-Reinstalled the tail pipe packs from Bassani in hopes it would create a little more back pressure to better heat up the hi-flow cats
-Drove the car on the freeway for about 20 min immediately before the test

Hopefully this thread will help someone else having the same problem.

Note that my NOx was still high, and could've probably been taken down below average with a new, non-hi-flow cat. But who cares. It passed!

Thanks again!
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Friday, October 31st, 2008 AT 3:28 PM
Tiny
RACEFAN966
  • EXPERT
Great glad to hear you past the test thanks for the update too.
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Saturday, November 1st, 2008 AT 12:09 AM

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