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89' nissan 300zx

This car passes a smog test at 25mph but fails at 15mph. I’ve tried a smog treatment add to the tank,warmed it up by drive fast in low gears and it still fails.Any help would be appreciated.


I’m really glad I don’t live in whichever state you live in.

'89? C’mon, how many 1989 ANYTHINGs are on the road, and how much impact on the overall picture can they possibly have?

I can’t help you, but I wish you the best of luck.

Please tell us which state (of the union) you’re in.

Would you please post the actual pollutant values and the limits?

Well, my fuel injected '88 Accord still passes the treadmill test with the original converter and O2 sensors at 218k miles.

I don’t know if this will help or not. Two years ago my 93 Caprice barely passed NJ emissions. The readings were 80 to 90% of the max allowed values. This time the Caprice passed with flying colors, the readings were 20 - 25% of the maxes. The only difference was that I drove about 50 - 60 miles the day before I took it for inspection. The spark plugs, wires, and distributor cap and rotor and were changed prior to the first inspection and were about 3 years old at the second inspection.

It would help to know what tests (CO, etc) the Nissan failed and the values. Other more experienced members of this forum than myself may provide better advice.

Ed B.

P.S. Don’t forget the basics like a clean air filter, fresh oil, and a tune up.

How many miles does it have on it, what’s the maintenance history if any, how’s it running overall,

and most important…what were the readings?

An oil/filter change, using one of those ‘oils for high mile cars’ might help, just a (low cost) guess. When’s the last time you had plugs put in?

I have an '88 Toyota Supra that still passes with flying colors. And I do none of those ‘fool the test’ crap.

Tdwag31, please post the test results. They will help us know what is not working.