Quote:
Originally Posted by Franke
Can anyone tell me why a 1990 LT5 would fail emissions with 3.9ppm Nox? The car has 55,000 miles on it and runs great. The max Nox limit in this state is 3.5 ppm. The HC and CO are well within limits. Some emissions people tell me to check the EGR but I don't think the LT5 has a EGR. The local Chevy dealer thinks the cats are failing but can't go any farther. Any help would be appreciated.
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You could be running lean. Did you dump out any codes that maybe set? Like maybe 44 and/or 64 ?
See the bottom of page 6E3-B-6 in your FSM.
Not likely at all it's the Cat.
O2 sensor(s) very possibly.
In any event you're so close to passing that another try with the car when it's not running as hot could pass. Let it cool before getting in line.