Car Smog Fail Help: High NO

[parasolution]

Failed smog in Alameda county in Northern California a couple of weeks ago. Been doing repairs, just need to make sure everything is good, will probably get a pre-test done to verify. Car is a 1990 SOHC with 180K and all stock.

Basically, I went into the test too complacent as I had lived in a non-enhanced area for the last several years and a smog test was never an issue. I just moved back to the Bay Area where the standards are tougher and require a dyno and NOx test. I had changed the oil and the car was warm, but I had old gas, a pinging motor, leaky exhaust manifold and a failing water pump (didn't know about the manifold and water pump until after the test). The car also doesn't get driven much so it had been sitting for a few months.

With all that said, the car passed everything except for high NOx. Complete reading:

15 MPH Test: %CO2: 14.9; %O2: 0.2; HC (measured/max): 18/85; CO% (measured/max) 0.11/0.54; NO (measured/max) 984/565
25 MPH Test: %CO2: 14.9; %O2: 0.1; HC (measured/max): 13/67; CO% (measured/max) 0.08/0.45; NO (measured/max) 943/522

From research, these numbers point to a bad EGR, vacuum leak or exhaust leak. As for the EGR, I applied vacuum to the EGR and it holds. I also lifted the diaphragm while idling and the motor stumbles. Based on these test it would seem I have a working EGR. I also revved to motor to 2300 RPM and checked to see if the diaphragm opens, but it didn't. So I checked the BPT and it was leaking. That was replaced, but I still can't seem to get the EGR to open as the revs increase. Does the diaphragm quickly lift as the revs increase or does the system have to build pressure first?

Also, I checked all the vacuum lines, there were no leaks, but I went ahead and replaced all the hoses since they were original. I also checked the EGR solenoid and its working properly.

In addition, I replaced the fan clutch, water pump, PCV valve, air filter and spark plugs. I also sealed the exhaust manifold leak. Car is driving much better and there is no pinging. Do I have this nailed down or do I also need to remove the EGR pipe and EGR and clean it thoroughly.

I'm a little concerned that I can't get the EGR diaphragm to lift as revs are increased. Is that still telling me that the EGR is not operating properly?

[Kon036]

A vacuum leak would make you run rich and cause your ecu to increase fuel trims to compensate, but based on your CO, O2, and HC levels thats not the case.
A exhaust leak would also make you run rich, but again, your CO, O2, and HC levels say otherwise.
Like you said it could possibly be EGR, but it could also be carbon deposits (hot spots) in the engine that could possibly cause high cylinder temps, timing too advanced, or the reduction side of your cat could have failed.

[AHall]

I have a very similar problem that I have been diagnosing of and on for over a month now. What I have narrowed my problem down to is either the ECM is not telling the EGR solenoid to shut off, or there is a problem between the ground wire from the ecm to the solenoid and maybe the BPT is not allowing the vacuum to flow from the solenoid to the EGR valve as a result of the back pressure from the exhaust. Have you tried unplugging your EGR solenoid and rev'ing the engine to see if the EGR valve functions properly? This would eliminate a problem with everything other than the EGR solenoid and the ecm. I would check for a vacuum from the solenoid when the engine is rev'ed. Then move on to the BPT.

By the way I have a 93 KA24DE.