Emissions fail - high HC

[wanman75]

94 V6 XLE failed emissions with high HC for the second time. First time it failed with high NOx as well, but new plugs seem to have cured that. Also replaced air filter and PCV.

Comparing with my 2003 emissions test, HC is up from 0.01 to 1.05 ppm and CO is up from 0.01 to 4 ppm.

From forum searches and other research, sounds like one or more of:

- bad cat
- vacuum leak
- leaky injectors
- faulty O2 sensor(s)
- EGR system problem
- faulty termostat

Are any of these more likely than the others? Any other likely culprits?

I'm also wondering why it hasn't thrown a code. Is it possible to have a faulty O2 sensor but no CEL?

[touringcamry]

I am fairly certain that if the EGR has a problem, the computer will throw a code. I am not certain about the other problems.

But high HC generally means that the car is running rich which is a result of the above mentioned problems.

[wanman75]

Bad O2 sensor(s) and/or leaky injectors being the most likely?

If it's not the O2S, the only thing I'm not sure about diagnosing/repairing/replacing is a leaky injector. Can it even be repaired, or is that an R&R?

[Doctor J]

Check if there is a vacuum leak or over advanced timing. The car running rich will have high CO above .9 percent

[wanman75]

No vacuum leaks that I can find. Timing is all ECU controlled, no?