1993 Ford Mustang Failing California Smog - Possible EGR Sy

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!