'03 Avalanche problems

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Hi,
It's a 1500 5.3 all stock. I put the old plug wires back on this afternoon and got the same results. Your guesses sound progressively less expensive, an O2 sensor would thrill me.
Would a bad injector cause the random misfires? Wouldn't a code come up for any of those issues?
It does still have the original exhaust system, I've never had one last this long actually. Is there an inexpensive way to determine if it's the Cat?
Thanks for your input, you guys are great!
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James Horn wrote:

If it is the catalytic converter, it might still be under warranty, even tho' the rest of the truck isn't.
Bob
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wrote:

If one bad injector, probablyi not, as the ECM would indicate which cylinder, and you seem to be seeing it on all cylinders. Tried viewing live data and watching the mis-fire counters?

Measure the pressure differential between the cat in and the cat out...

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