CL-Fault... where to begin?

[danhr]

Ok I know the answer to my question, and I don't.

Got a vehicle that I'm going to start modding, and figured I would try tuning myself this time around.

Got the vehicle and it has a misfire, I throw the scanner and figure out the following:

1)CL Fault - ok... I'm only running on one o2 sensor. one bank's fuel trim was slightly negative

2)Check the upstream o2 sensors... both seem to be working fine... both go back and forth between 100 mv and 800 mv

3) Duty cycle is through the roof... 100-110% at idle.... rev it to 2000 rpm, and I'm at 300%. Didn't want to go any further than that.

4) Downstream o2 sensors are stuck at 252 mv

5) Doesn't seem like there is a vacuum leak

6) I just replaced the spark plugs because I had an extra set laying around

7) Fuel pressure is ok (60 psi for a 4.8 LS motor)

8) Getting a misfire very seldomly

So should I assume that I have a set of clogged cats? It seems odd that I would be running on one o2 sensor, when both banks are acting the same.

Sorry if this is a dumb question. Figured I'd get some input before I start throwing parts at it.

[joecar]

3) Duty cycle is through the roof... 100-110% at idle.... rev it to 2000 rpm, and I'm at 300%. Didn't want to go any further than that.

several things can cause these symptoms:
- air leak at intake manifold,
- air leak at exhaust manifold/header (influencing front O2 sensor),
- "worn out" front O2 sensor (they still switch, but more slowly),
- injectors sticking (they fail to open sufficiently).

Clogged cats may cause similar symptoms, but you will also notice lack of power, poor revving, lack of flow at exhaust output tips.

I would get new front O2 sensors, remove and inspect cats (substitute a test pipe and see how it runs), check injector balance (from scantool, turn off each injector one at a time, if rpm does not drop by about 50 rpm for a moment then that injector is not flowing sufficiently).