O2 sensors in van?

[Testarossa]

2007 Chevy Express 1500, 5.3 liter V8. 350,000 miles. During the last trip to California one of the spark plug insulators cracked and I ran 1200 miles home with that cylinder misfiring. Burned a lot of fuel and undoubtedly ran rich, putting unburned gas through the catalytic converter.

All fixed now (all new plugs, intake manifold gaskets, knock sensors etc) but a couple of days ago the check engine light came on. Code reader said "cat converter inefficient," which usually means inconsistent readings from the O2 sensors, one or both. I erased the reading and it hasn't recurred, so I'm assuming this was a one-time response to the high-speed misfire. Can anyone confirm that theory or suggest a better diagnosis? What's the likelihood I cooked the cat?

[nc43bsa]

Given the circumstances you described (misfire for long distance) you probably ruined the cat.  You could try replacing both O2 sensors first, on the off chance that one of them is faulty.

The misfire should have turned the CEL on.

[Testarossa]

The misfire should have turned the CEL on.

It did. I read the code and it called misfire on cylinder 3. It was a Friday evening, I didn't have tools, and I couldn't get anyone to look at it on Saturday. We needed to be at home Sunday night, so we just drove.

Cross fingers the CEL doesn't come back on. If it does, maybe $150 for O2 sensors and $500 for the two cats and plumbing.

[nc43bsa]

I'm not intimately familiar with that model van;  does it have two O2  sensors or four?

[Testarossa]

Four. Upstream left and right, downstream left and right. I'm guessing $35 each.

[flangeman_70]

You could try regeneration on the cats if the internals haven’t melted.
The O2 sensors could also need to self calibrate in some applications.
Are post and pre cat sensors the same type? Swapping will help you troubleshoot.
Check your local web for more details.

Adam

[Two Checks]

The O2 sensors and cat could be fouled with carbon deposits from running rich. Try some mechanic in a can f the cel comes back. Ya never know it may work. If you do need to replace sensors use NTK. The Bosch units tend to be lazy.

[Testarossa]

Thanks for the advice!

[pat80flh]

I'm assuming the last code you set was a P0420? catalyst inefficient?
  Doubtless you've at least damaged the cat due to the unburned fuel, from misfire.
If 0420 is the only code, it's cat .  If there are no oxygen sensor codes, it's probably not an oxygen sensor.
 
   The 2 front oxygen sensors are used strictly for fuel management.

    The two rear oxygen sensors are used strictly to measure catalyst efficiency.

     

[Rough Edge racing]

 I'm aware of Chevy LS intake gasket issues.....Where the gaskets leaking when the spark plug failed?  I also think the convertor may have seen better days...It should have a cat on left and right bank...

[Testarossa]

Yes, the intake manifold gaskets were leaking (though I didn't know it) when the plug went bad.

Two cats, one on each side. I replaced them at Midas 18 months ago when the junction to one exhaust manifold failed just before a big ski trip. Can't recall if the sensors were replaced at the same time. Paid $1000.

No code at all right now -- fuel mileage is back where it should be and no other abnormalities. I'll motor until the CEL returns and then deal with it.

[sidecarnutz]

We had a cracked distributer cap on my wifes car in the 90s. Caused a misfire. Just driving it back from work that night caused the CAT to melt to slag and get flaming bits of it ejected out the tail pipe. Interesting to watch in the rear view mirror. Just needed a new CAT installed after fixing the ignition.