Infiniti M56 code P0420 and strange metallic noise

[Khannsaad]

I recently picked up a used 2011 Infiniti M56, initially the car had low oil level, hesitation when accelerating from a stop, a P0448 code (no engine light), black smoke upon hard acceleration, and metallic sound during crank/start up.

Previous owner informed me the car Had been sitting for 5-6 months, has had aftermarket high flow cats put in as the factory ones failed.

I went ahead and changed the oil using Redline 5w30, along with a K&N oil filter. New air filter (old ones looked as if never changed), and changed the pcv valves. This took care of most of the sluggishness.

Now I am getting a code P0420, and upon start up there is a strange metallic noise, and very slight shudder which can be felt in the foot area of the passenger seat (closer towards the seat), the car is using a lot of oil. I feel as if the cat might have never been changed and that it is clogged, there isn’t a rattle but a strange sound only when starting can’t tell where it is coming from.

I want to gut the cats out, as I heard to replace you have to take the engine out of the car, can someone tell me if it is possible to cut and gut the cats from under the car, also if someone could tell me what might be causing my crazy oil consumption, I don’t think the black smoke is present now, but I read through forums that burning oil is blue smoke not black.

If someone could advise me or have had a similar issue, also who might have more knowledge with this vk56vd engine could give their opinion, it is much appreciated.

[VStar650CL]

P0420 is a cat code for bank1 (driver's side). If your rattle is coming from a disintegrating core, you should be able to reproduce it by banging on the cat or downpipe with a deadblow hammer. If that doesn't make any noises from inside the plumbing then it isn't a bad core. If the cats really are new then the noise could simply be a heat shield that's damaged or not installed right. It's pretty common for aftermarket cats to cause issues with the A/F's (front O2's) or rear O2's, particularly if the installer created air leaks or used aftermarket O2's. That can fool the ECM into thinking a good cat is bad. You can check for leaks by having an assistant block the exhaust with a shop rag, that will turn even a tiny leak into an audible air cannon.

It's correct that oil smoke is blue, black indicates a rich mixture. If there's no blue at idle, you still might have bad valve seals. Those only produce clouds under load when you work the throttle, so have someone drive behind you while you on-off the gas. If it spits little blue clouds every time you accelerate, the valve seals are shot. Running rich can also cause oil consumption, because the blowby thins the oil and sends it out through the PCV's. If that's the problem your new oil will quickly smell gassy and eventually the car will throw a P0172/P0175.

[Khannsaad]

I appreciate you taking the time to respond, so as for the P0448 evap code, it’s not present anymore, and the cat code comes on about 150-200 miles. This cat code started after replacing my oil, filters, and pcv valves.

I had the car up on the hoist and honestly the cats on it look factory, there is some seepage from my oil cooler o ring but not nearly enough for how fast my oil is going down, I had done a health scan on it, the read outs were great except for my intake valve timing, my bank 1 intake valve timing is reading the same as bank 2, is this normal? I will attach a picture of it.

My friend mentioned that if the timing were off by 45 it would be very noticeable, such as loss of power, clatter, and or overheating and what not. Yet the car drives great and my fuel economy is great.

Now i’m stressed about the cat code and the timing.

[Ilya]

I've had a P0420 for like 5 years...I just masked it with an O2 sensor spacer and haven't noticed a difference hah.

As was stated, unless you take a dead mallet to the cat and hear it rattle, it's likely your cat is juuusstttt slightly under efficiency triggering the code. Many on this forum believe Infiniti is very sensitive.

[VStar650CL]

Those cam readings have to be a scanner artifact, it couldn't possibly run right at those angles. In normal operation it should read zero at idle and about 30 degrees max during acceleration. Many aftermarket scanners don't handle the cam angles correctly, I think that's the case here.

[Khannsaad]

Ilya, thank you for your advice I actually saw your video on youtube, my concern with that was I heard through forums that on these VK56VD motors since the cat is part of the manifold, the disintegrated pieces can get sucked back into the engine and cause damage. A guy local to me told me that it won’t go back up in the engine but instead clog and damage the secondary cats.

Though I will give that hammer test a go to see if I have any pieces or a heat shield loose.

As for Vstar, once again I thank you for your feedback, I was thinking the same thing, this read out on the scanner is taken at idle, and seemed very off to me, if it were so bad I’m sure the engine would be gone by now, though the car runs great, and pulls hard.

I will try to upload a video on youtube and link it here as to the sound I am hearing, as I don’t see an attachment for video on the forum

[VStar650CL]

Anything Nissan which uses Miller-cycling can suck in the cat, and that encompasses practically everything from the late '90's onward. It's actually pretty common on VK56's. The only engines where it's very infrequent are longitudinal VQ's. However, your local guy is correct that they disintegrate much more often than they melt, so it's a relatively small risk. Just be aware that it has catastrophic results if you roll snake eyes.

[Khannsaad]

Would it be advisable to just for safety gut the cats out, there is no emission worries here

[VStar650CL]

If you're in a non-inspection state then there's no disadvantage to coring them, aside from needing to dummy the rear O2's. Just remember never to run it with the garage door closed, and warn your mechanic not to do it either.

[Khannsaad]

Thank you for the help, much much appreciated