TheBigDogg

Lat october I did a smog check on my 89 XJ and it failed bad, there were parts missing and vacume lined plugged, well i fixed all that and took it today to get smogged, since the last smog I ran some Lucas fuel injection cleaner on about 3 tanks.

check out the attachment, in the Oct 2009 test, CO(%) failed at 15 & 25 mph, anf HC failed at 25 MPH

todays test failed just on the CO(%) at 15 mph

please help me

TheBigDogg

can someone help me?

Abovetimberline

What have you done to it besides the items you mention here,it is running rich,it would not be uncommon for it to fail at 15 mph vs 25,do they do a test at idle,it does not look like it. Which I find strange because at idle,it would fail even worse.

TheBigDogg

yeah i know it is running rich, I am going to replace the O2 sensor and see what happens

Abovetimberline

The 02 sensor may help,how long has it been since the cat was replaced,tune-up done? You can check the sensor,once your jeep is warm just back probe the sensor and the volts should be between o to 1 volts

TheBigDogg

the smog guys thinks it doesnt need a tune up because how smooth it was running, he thought it would have no problem passing, he is going to test it for free when i go back, he said if it was the CAT, that the HC would be higher

Abovetimberline

The cat could be worn a bit,the #1 enemy for a cat is unburnt fuel,with the issues you had you probably did some damage to the cat,mine was close and all I did was change the cat,if your cat is older it would probably pass with a new one.
here in ca they do a dynamic test like yours in populated areas,here where I am they only test at idle and 2000 rpm,without a good cat they will always fail at idle.

JrRifleCoach

When my 86 VW failed, the fix was to back off the timing 2 deg. This moves more heat out the exhaust to help heat the cat. Car passed on the second try.

I also let the fuel level run down to a few gallons and dump in a pint of alcohol. This helps reduce the hydrocarbon count. Take it for a spirited run and show up for your appointment a few minutes late so the engine and cat are nice and hot.

These measures will make small changes to assist a marginal engine.

However a local shop subscribes to replacing the cat because a new cat will hide a lot problems simply because its new. That may be an answer as well.

RevZeroX

have the cat pressure tested. also, run it hard before retest.

smokinlib1

My 90 failed first on NOX, got that fixed and then it failed CO. Fixed the overheating problem which fixed the NOX then replaced the O2 sensor and passed smog. If you google your question you'll find page after page of what to look for for high CO. That's how I got the info to fix mine.