I think I've knocked out most of the easy/cheap ones.

Clean MAS - Done 11/2015
Clean Throttle Body - Done 11/2015
Change Air Filter - Done 9/2015
Change PCV Valve - Done 7/2016
Change engine oil - Done 7/2016
Change MAS
Clean Fuel Injectors (profeesional service not just a bottle of juice in the tank) - Done 7/2016
Change O2 sensors
Diagnose fuel trend issues
Diagnose possible vacum leak
Change conveter
Fix engine oil burning problem - Done 7/2016 (was a result of the PCV failure)

 

Throttle body and PCV valve are cheap and worthwhile too, even if they aren't acting up...depending on age/mileage.

 

A P0420/430 fault can only be caused by low cat efficiency.

Low cat efficiency can be caused by many other factors though, such as contamination of the cat substrate by oil or unburnt fuel in the exhaust.

If your PCV valve failed and caused excessive oil consumption, you need to clean it out before it can fully coat the inside and carbon to the point where chemical cleaning will not work.

When I see this, I usually perform an induction service, with the addition of a different chemical, I use BG211, which is more aggressive than the BG206 that is normally used to clean the intake system. The BG211 is designed to help clean carbon deposits from the EGR tube, so it's made for the hardened, baked on stuff, not the oily/waxy build up that the 206 is designed to clear.

The key to having it clean the cats is that you need to start the service when the engine and cats are cold, and raise the idle enough that it doesn't completely burn in the combustion chamber, usually steady around 2-2500 rpm, with periodic throttle sweeps to 'blow' out the cats. You will want to follow up with a can of 206 to clean out any residue from the 211, as it is aggressive and can cause rubber gaskets(and even the PCV valve diaphragm) to prematurely fail.

I have had this work many times, and not work several others. The main thing is how long the oil consumption has been going on prior to attempting the clean.

 

So in other words, it wouldn't do any good to try replacing the O2 sensors first to see if that resolves the issue?

If the O2 sensors are fouled, couldn't it trigger the same code?

Just hoping, since the O2 sensors are much much cheaper and easier.


Also noticed the code only seems to come back if I drive it relatively hard (i.e. RPMS of 3,000 or more). If I keep it very tame, the CEL doesn't come back until I push it again.

 

O2 sensors will not cause this, at least not directly.

For these faults to throw, it needs to see the downstream O2 reading switching faster than it should, with relation to the upstream. If an upstream sensor is switching slow(lowering the period of up to downstream switch) it will set a O2 sensor fault before it sets a cat fault.

That said, if the upstream is failed in a way that it is reading lean, it will cause the PCM to enrich the fuel mixture, which can lead to excess fuel into the cat, which can then lower it's efficiency, however, for it to have enough of an effect on the cat to significantly lower it's efficiency, it should set a fueling or O2 fault long before a cat fault.

With what you're seeing, I would suggest having an induction service to attempt to clean any fouling that is in the substrate(as described above) before replacing any parts. A new cat will rectify it, however that may very well be an over-repair at this point. Keep in mind that you were probably burning a moderate amount of oil for a while before replacing the PCV(it doesn't need to be smoking to be burning oil), and if nothing else, an induction service will help clean up the rest of the fouling caused by the failed PCV valve.

 

I think (and I'll have to double check) the shop already did an induction service. Someone else suggested taking the cats off and back-flushing with water...would that have a chance of working?

Since money is tight, would a used catalytic converter from a 2005-2006 LR3 work for a 2008? Were there any changes in the cats across the model years?

 

Was the induction service before or after the PCV valve failure? Do you know what chemicals were used?

I can't think of a difference between the cats, so I think it should fit.

Just water probably won't do too much. If removed, I would try a solvent based cleaner, and then rinse with a detergent and water. Expect a good amount of smoke from the exhaust when re-installed. This may help, but if the fouling is too baked on, it may not be enough to clean without heat as well.

 

I just got my LR3 back from the Indy shop I trust with CEL issues and same code. They said the mass air flow sensor was fried DUE to the K&N filter . They said it was fried from sucking the oil off of the K&N filter and suggested I immediately go back to the paper filter. And put in new mass air flow sensor . I am also told a bad capacitor could throw the same codes . A new capacitor and air mass filter are on their way. Hopefully one or both will fix the problems.