P0420

[richarcm]

I've owned this 2004 Xterra 3.3 since September. And I've spent the majority of time working on it fixing problems. I thought I was buying something that would "run forever". Seems it will only "run forever" as long as you are fixing problems on it every other weekend!!!

The last of my problems is this P0420 code.

From my research this is most LIKELY either a cracked manifold or a bad cat. Either way it would require removing the exhaust manifold. I've removed the manifold heat shield and I don't see any cracks. I'm assuming the cat is bad. But it does run rough and I don't want to drive it until this is fixed.

The bolts all seem to be fairly easy to access. But I know that the rust will be the bigger headache.

• How difficult is it to remove these manifolds (in a driveway without air tools)?
• How expensive is labor to remove this at a shop?
• Do you replace with stock components or aftermarket?
• If you replace with aftermarket, will there be any noticable problems leaving the factory exhaust on the drivers side (until it too goes bad)?

This truck is SUPPOSED to be my daily driver. I am having to drive my weekend car until this is fixed. Which doesn't bother me except I want to keep the miles off of it and IT needs repairs done as well. Which i'd like to do once I get the Xterra running again.

 

[Prime]

First things first, O2 sensors. You can get them on Amazon for about $25 each. Replace those before you worry about manifolds and cats.

 

[richarcm]

Thanks. I went ahead and bought the two for the passenger side. I figured even if it is the cat, when I changed the cats out I’d want to replace the O2 sensors anyways.

We shall see if that helps. But either way I think the cats are on borrowed time....

 

[Gen X]

If Prime's suggestion doesn't work...

I had the same issue when getting my X last year, but I had codes for both primary cats. OE primary cats are unreal expensive. I had a local shop quote $500 each plus another $500 for basic labor. I did what most do, went with long tube headers which eliminates the primary cats and replaces the manifold. Originally the plan was for Doug Thorleys as most people use. But, I couldn't get the downstream 02 sensors out so decided to replace the secondary cats as well. Hindsight on this one, I would have spent a bit more time yanking and PB blasting the sensors to get them out. I would have been able to afford Thorleys. But, instead I went with eBay special knock off long tubes and secondary cats. I passed on having the shop due it and did all in the driveway without air tools. It was surprisingly easy to do. You will need to disconnect the primary cats from the manifold to get all those pieces out. Luckily, with PB blaster, the bolts came out easily. Same for the manifold studs. Since I was scrapping the secondary cats anyway, I just cut between those and the primary cats with a recip saw. I put on new downstream 02 sensors. You will need to extend the passenger side upstream 02 sensor as the stock length won't reach to the new location with long tube headers. Just a short extension of about 6 inches works. I cut pieces of wire from the old 02 sensor and soldered them in. Only cut and solder one wire at a time so you don't get them confused. Use some heat shrink over the soldered connections. You'll need CEL eliminators to put between the downstream 02 sensor and the bung where they connect. This removes it from the exhaust stream and makes the computer think you have primary cats. It took me a couple days work over the weekend to get it all done. Cost was about $650 which included all the parts and pieces plus some tools needed for the job. No more check engine light and it's been running fine. If you have a little mechanical experience, you can do this yourself if needed. The savings is worth it. Thorleys are about $450, so less than one OE cat. If you can swing that, most on here will recommend them. I've never seen Thorleys so can't comment on how they are in comparison to my eBay cheapos. The ones I bought were pretty solid with good welds. I did have issues lining up one of the manifold studs on the driver side. Nothing a few swears couldn't fix.