What Say You SMOG FAILURE

I recently obtained a 1994 XJ12 that has 98k miles on it and did not pass California Smog. BAD on all items.
Well I just got done putting new plugs, wires, cap and rotor in it. I do not believe the plugs were ever replaced. They were at .035 and one plug was not firing. Do you all think this could be the reason it failed smog??? I plan on also putting on a new O2 sensor and driving the heck out of it before I try smog test
Tanks
Mike

California SMOG tests are very, very exacting. New plugs will certainly help especially if one was not firing at all. Do change the engine oil as contaminated oil can create fumes that are drawn into the engine intake via the crankcase breathing system. California, I understand, also verifies that the fuel tank vapor recovery system is intact and operating properly. Your fuel filler cap will also be checked. Before the test make sure you have driven the car hard for 10 miles and make sure the tester tests your car IMMEDIATELY after your drive when the engine is at full operating temperature. Were any “check engine” malfunction lights illuminated? If so, have a shop read the codes and address these issues prior to the test. Do report back with the results of your next test. I wish you the best of luck.
/s, a former CA resident who escaped for Oregon

Also make sure that the thermostat is allowing the engine to reach full operating temperature. I have a 1993 XJ6 and it never failed emissions here in NJ. I just made sure that the plugs, cap, rotor, wires and thermostat were good. Bosch platinum plugs with the four firing points are fantastic for clean emissions. I swear by them.

If the car has been driven for a while with the plugs so worn and one not firing at all, chances are the exhaust system and cats will be dirty inside with the the unburnt fuel that’s been passing through them.
Sometimes a good long fast drive for an hour or so can be enough to clean out the system.
Here in the UK there is a product called Cataclean that you pour into the tank. If you can get it where you live and take the car for a good long blast it will clean the cats and fuel system. This will definitely improve the emission readings all round and may even bring them down to within range with one treatment.
I was sceptical when I read the claims on the bottle but it definitely works. My sons 1996 Mini failed the UK emissions at the recent MOT test, we added one bottle and followed the instructions, without doing anything else the car sailed through the tests.
good luck

casso
Yes that is what I planned on doing after I get it all back together, we have the Cataclean here in the states.
The one that was not firing was almost at .40 wide. I just think that was the problem because smelling the exhaust you could smell raw gas smell.
Hope it is a cheap and easy fix.

mike

Is your engine consuming oil noticeably?

No color whatsoever out the exhaust. So I would say no, since it is a new purchase.

It might help if you can provide the results of your last smog test before the one you failed. And the time interval and mileage that you drove.

Used to get all my old cars thru emisions by running to almost empty, add 2 or 3 bottles of stp and a 1/4 tank of high test! Run for one hour and never failed!

The reason I ask for the oil consumption is that when the valve guides wear, some oil gets past them and into the chamber. Oil burns poorly and lots of CO, NOx, and hydrocarbons get into the exhaust manifold and towards the catalytic converters. The cats are very good at reducing NOx, oxidizing CO, and finishing the oxidation of light hydrocarbon fragments, but partially-burnt oil is too much for them, and will over time saturate cat surface and make them both inefficient and clog them up. So you end up with failed emissions on all 3 California components (NOx, CO, HC), and your engine power is half what it should be. Without taking apart the engine to measure the valve guides, a good indication is that you are down a quart of oil every few hundred miles, absent the oil leaks. If the guides are at fault, replacing one of the cats will get you through CA emissions, but also replacing worn guides will be the solution past 12 months. Again, assuming oil loss past valve guides.