2003 blowing blue smoke

[Slartibartfast]

The clogged cat theory sounds good. Is there some special OBDII test that could verify this via O2 readings or increased fuel delivery? We'll do a smell test on the oil and see if we can detect any gas. Dad suggested having a used oil analysis done to confirm blow-by, but given how much fresh oil we're adding, would the oil stick around long enough to be worth testing? Given that the cats run about a grand just in parts we'd like to be sure they're the problem before buying new ones.

 

I've heard of the Maxima guys punching out their cats and putting the second O2 sensor on a spark plug anti-foul spacer to make the computer think everything's normal. We have no emissions testing around here obviously, and given how much oil's going through this thing I'd be surprised if the cats aren't in a bad way already. Even if the computer threw a low catalyst efficiency code, would that make it quit dumping gas?

 

I would like to check the valve screws just to be sure. Two questions on that. First, if we pull off the upper intake and find bits missing, should we assume the motor's shot? And after checking/loctite, can we get away with re-using the gasket? If we do solve the oil consumption it'll likely get new intake gaskets and a new PCV just to be on the safe side, but until we know there's hope for this engine we'd rather not throw new parts at it.

[Towncivilian]

Used oil analysis won't detect blow-by.

 

I'm not sure about your second question.

 

The gaskets (TB, two UIM gaskets) are supposed to be replaced per the FSM, but they are metal-backed so if they're in good condition I can't see why you couldn't reuse them after cleaning them and the mating surfaces.

 

If one or more power valve screws are missing, there may be engine damage or catalyst damage or probably both since you are consuming so much oil.

 

PCV is buried under the LIM and you *have* to take it off. So if you're tackling the PCV, do the threadlocker on the power valve screws with it off the vehicle so it's much easier.

[River044road]

It does sound like valve seals, but it seems odd that they'd fail so early. I would also expect it to smoke on cold starts, and it doesn't.

That might make sense though because it takes a while for oil to get back up to valve train.