<>Failed Smog Check . Hi Doc, Sorry for the delay. I have a fairly new computer and it is doing some strange things. Plus things are not always where they should be.. All the HC and CO tests passed. The NO passed at 15 mph but failed at 25 mph. The MAX should be 1224, the AVE is 468, and mine was 1315. I was told I needed a regular gas cap instead of the locking cap I had on the car. I now have a regular cap. As I mentioned, the mechanic said 'there was no vacuum coming from the throttle body unless it was cranked hard.' He thought it might start getting expensive trying to work on the car further. I just had a bad feeling about all this.. E-mail me when you get a chance. Also, have a great time with the kids at Disneyland.. Thanks, Gene . Hi Gene, Doc here, it has been about two years since I saw your "Z" and we got it from a Gross Polluter to a very low emission range and passed the 'Exam'. The numbers that you have right now reflect the CO (fuel) and the HC (unburned fuel. The NO, or NOX is nitrides of oxygen and are a byproduct of the "fuel" that we really don't have now. For all the mileage that you have the engine is running great. It is also possible that you are ready for the valve adjustment and that will have an effect on the 'exam'. If you take my suggestion about the oil change thing and the other suggestion then we will know the results of this operation and the effect that it has on the 'exam' tailpipe report. The scientific method is to do one thing at a time and then test the result to prove the operation procedure. I have seen some products that claim to get your car to pass the 'exam' by some chemical property added to your gas tank. I have not personally tested them, but they claim good results... The overall readings for the age and mileage of your "Z" are a remarkable testimony to the design and engineering potential of the car. Longevity is a wonderful thing and we ALL owe a debt of gratitude to Datsun/Nissan for their efforts! What we have now is the result of a political system with an agenda to get the older cars off the road through the process of rigging the test. The MTBE fiasco has been willingly and knowingly been a bad example of the doctored evidence and put the stuff in our gas tanks and then in all our water supply. Why didn't they immediately stop putting it into our gas when they found out what it was really doing to the public health issue? But never mind. The tests conducted with the out of state gas and the California stuff on the same vehicle are proof positive that the fuel is the way to cause the vehicles to increase the emissions and cause more pollution in many other areas too. OOPS! I'll get your test results back and I believe that you will pass the test, so please report the findings to me. I hope that this helps you.... ZDOC OUT... :^). Gene O'Riordan wrote:. Hi Doc, I just got your e-mail. I'm having trouble with the AOL mail system. I have much better success with Yahoo.. At 15 mph HC = 98, CO = 0.15, and NO = 1006. Pass. At 25 mph HC = 78, CO = 0.14, and NO = 1315. FAIL. I have 214,000+ miles on the car. I also have my fingers crossed. I'll try your suggestions and get a retest on Monday or Tuesday. I'll let you know how things turn out.. Thanks again, Gene. Hi Doc,. I talked to the owner of the SMOG shop about the previous test. Evidently they tested the car with -8 degrees BTDC. They were busy so I didn't want to wait around. I decided to take it to the SMOG ONLY center. The new gas cap and the 20w50 oil change did the trick. The new reading are: 15 mph HC = 107, CO = 0.37, NO = 1097, PASS 25 mph HC = 73, CO = 0.72, NO = 1077, PASS. If it didn't pass I was thinking of going to Reno and get a tankful of the good gas. I was wondering what grade of gas to use. The Datsun manual said 92 octane but an article in SportZ magazine (I think it was SportZ) said to use regular and never burn more than mid-grade(89 octane). That seems strange.. Anyway, thanks for your help. Sometime later in the summer or early fall I'll let you do a valve adjustment. Maybe we can keep it running a while longer.. Till later, Gene.