1990 Accord EX passed smog test but with extremely high NO for a HONDA. Suspected EGR valve but tests OK. EGR control solenoid valve tests OK and there is a constant 5" vaccum from Constant Vaccum valve. Suspect ECU or input to ECU.

Question: What inputs does the ECU use to determine criteria to activate the EGR control solenoid valve?. I suspect engine speed and temperature are in the process but any more? I suspect the engine is running hot therby making high nitrogen oxides but don't know if it is so hot to take out the Catalatyic converter or anything else.

Any suggestions or answers?

first how many miles you have in your engine, it sounds like if the catalatyic converter is bad, inputs egr sensor, temp sensor, oxigen sensor, vac sensor, if evrithing checks fine all this sensor and catalatyic converter, it will be the driver that controls the ground side to the vacum valve, and remember it has to be 8" of vacum to the egr not 5

Car has 215K. Been researching this problem for awhile but the priority to fix it is somewhat low as I don't have to try to pass the smog test for another two years. The vacuum from the constant vacuum valve is 5 in/hg and that could be the problem. Will need to hook a volt meter to the ECU side of the vacuum valve to see if it goes to ground with driving and 1800 rpm. If that works then it could be a cataylic converter or the EGR ports into the intake manifold. I hear they tend to plug up. So many possibilites and the only way you know if it is fixed it is to take it to a smog check shop and have them run it on the dynometer.