Does anybody know what is supposed to happen before the egr system actuates in a automattic '94 SR? The basic's I know, in gear, warmed up, and under moderate load. What I want to know is what sensor outputs are needed.

Maybe we could start with the egr solenoid voltage. The voltage at my egr solenoid varies from 0 at idle to battery voltage at around 2500 rpm.

And yes I'm asking these questions because of high nox. Here's the numbers:

15 mph co2(15.2) o2(0.1) hc(27) co(0.20) no(1565)
25 mph co2(15.2) o2(0.0) hc(16) co(0.18) no(1598)

Your cat-converter is probably bad, especially if it's an aftermarket part. You should have ZERO CO left over if the converter is working properly. The state of CA mandated a change in converter quality starting this January. They have to guarantee them for 5 years and they have to have a CARB EO (Exemption Order)to be legally sold now. I've seen the old style aftermarket replacement Cats fail in one year, and barely pass NOX readings when they are new. They skimped on the Rhodium in the substrate for cost reasons.

As far as the EGR is concerned, find the factory test procedure and see if the EGR valve is actually working. Usually if there is a circuit problem with the controls, it would throw a code and turn on the light. Most CA Mitsubishi's had a EGR temp sensor that if it doesn't see the temperature rise when the ECU turns on the EGR valve, a code will set and the Check Engine light will come on. EGR should come on at partial throttle, medium to light load, engine fully warmed up.

Thanks for the quick reply.

I've just been playing with it and found that my evaporative purge solenoid is always open with the engine running (I'm thinking it might be getting a bad signal from the MAF). This was causing enough vacuum leak to mess with the egr function.

The purge valve being stuck open would have more effect at idle, causing a lean condition/rough idle with a Mass air EFI system, but would not have much effect under moderate load or cruise, when it's normally supposed to be on. The HC reading is pretty low, and the high CO2 readings indicate good fuel mixture control, too.

The only way it might effect the EGR valve is if for some reason, the vacuum line to the EGR valve and solenoid were caused to lose vacuum below about 5" or so.

Do you have a vacuum pump to test the EGR valve? Can you loop a hose from a manifold vacuum port to the valve while you are idling? With vacuum at the valve, it should stall at idle.