Smog test problems

I have a 1990 used MPV my wife got for free from a friend to fix for the daughter & grand kids. Well, it's not passing the smog test here in CA. Nitrogen Oxides or NO's are twice the limit. After replacing the exhaust & a tune up we got them down to 65% above the limit. Any one have experience with passing smog test any where would be helpful. Also looking for the EGR valve, not sure what to look for. Any engine diagrams on the web any where?

Thank you, Lance

sorry not sure i think its on the passenger side of the engine block toward the rear

Well for what its worth. Took it to a local shop to have it diagnosed. No EGR on this engine. But, the O2 sensor & coolant temp sensor were bad. the O2 sensor was working just not in range. Thats why no check engine light. Found that Autozones web site has a component locator as well for any one in the furture.