Jaguar Repair: Smog, gas additives, air filter oil

Question
QUESTION: Hi Howard, i just recently bought a 85 jaguar xj6. I have changed the O2 sensor, spark plugs, cables, distributor cap, rotor, air filter, oil filter, and gave it an oil change. I took it to smog and it failed. I dont use gas additives. The engine doesnt overheat.

the readings were:
HC 79
CO 0.28
CO2 14.3
O2 0.1
NOx 1843

What do u recommend for me to change? or wat do u suppose can be the problem?

ANSWER: Hi Eddie,
Your test sheet should have given you the limits on each. I live in a state where they only require HC and CO to pass and the limits on HC is 220 PPM and CO is 1.2 and you are within limits on both.
CO-2 is usually out of specs when you have an exhaust leak. I don't know what your limits are in your state.
The same for O-2 and NOX. NOX is the Nitrogen in the air burning which is usually an indication the combustion chamber is over heating for some reason. Unless one of the two CATs is overheating. Your HC does not indicate raw fuel going into the CATs unless you can see the first CAT glowing.

Your HC and CO readings are not great but passing. You should do some testing like what is your fuel pressure (with vacuum and without). (32PSI w/vac and 42PSI wo/vac)
Also take a volt meter reading of the O-2 sensor to see if too much fuel is going to the first CAT. A volt reading of .5v is normal and .3 and less is lean and .7v or more is rich.
If you have a three wire sensor, the blue wire is the sensor and the other two are just the heater.

Howard

---------- FOLLOW-UP ----------

QUESTION: when u talk of the CAT your talkin about the catalyctic converter?

here are the readings again and their limits..
Hc..  79   limit:82
Co..  0.28 limit: 0.52
CO2.. 14.3
O2..  0.1
Nox.. 1843 limit:742

Answer
Yes, CAT is Catalytic converter. and your limits in NOX confirms my suspicions. Before you take the car to a shop that has the test equipment to give you an estimate on what is wrong, try what I said. Put a "T" in the fuel line just before the fuel rail and get a 0 to 50 or 0 to 100 PSI gauge. Auto fuel pressure gauges for fuel injection systems are a little pricy so I just bought a industrial gauge and it worked fine for several years before I got a regular gauge system. Be sure to put clamps on each hose connection and be sure to use pressure hose available at any auto parts store. All ser III XJ-6 cars have the Bosch "L" Jetronic injection system that operates at 32 PSI w/vacuum on the regulator and 42 PSI with no vac.

Your HC and CO readings are passing but too high. I have two series III XJ-6 cars and they both have over 120,000 miles on them and they always run in the HC = 20+ range and CO is always in the .1+ range.

You have to remember that these readings are at the tail pipe after two CATs. That is why I told you to take a 0-2 sensor reading with a volt meter because it is a good indicator of fuel mixture BEFORE either CAT.
If the fuel mixture is close to correct the 0-2 sensor will produce a .5 v DC. If the fuel mixture is too rich the reading will be from about .7 v to 1.0 volts. The sensor needs to be heated up first so you will need to run the car a little before testing it. When you unplug the sensor the heater will be disabled but that is only needed when the engine is cold or at low RPM.
Howard