help failed smog

my 88 xj just barley failed smog test in california. 15MPH NO was 1279. Max to pass was 1020. everything else was right in the middle. any suggestions

Install new Champ spark plugs. My NOX went down as a result of doing this. The problem you are having is related to a lean mixture.

My 1996 ZJ failed the TN while my 85 XJ passed perfectly. We got the ZJ to pass on try two by driving it for about 20-30 minutes before testing.

Try not to test cold.

try a service that cleans the top of the pistons and valves, chrysler makes a combustion chamber cleaner, just folow the directions on the can. we sell it for about 10 dollars

things to do.....

Fresh oil and filter change the same day you smog it.
Fresh air filter, fuel filter, and tune up on ignition system (plugs, cap, rotor, etc.). Run the tank low before and fill her up with an ethenal based fuel. Or if you have the money run it straight as it will burn clean. I have never actually seen anyone really do this last one. Have heard lots of talk about doing it but no takers. Look over the vacuum system and make sure you have no leaks.

Also there is the snake oil "Pass Smog Test" fuel additives. I do not know if they do anything but I am trying to give you more options. hope it helps

livewire said:

my 88 xj just barley failed smog test in california. 15MPH NO was 1279. Max to pass was 1020. everything else was right in the middle. any suggestions

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High NOx emissions is usually a sign of a lean running engine but since your CO/HC emissions are right in the middle, this seems unlikely. The '87-'90 4.0's have EGR and a common cause of leanness in these models is a stuck open EGR valve. Clogged injectors is another common cause.
It's just possible that your cat is going south and not cleaning up the NOx emissions so I think you should check that first. If it's gone, replace it with a Carsound high-flow unit.