You are fine with 265/75/16.

t

SES light is on and I've got P0430 and P0420. I'm stumped at this point cause the dealer just did the tune up and they checked it and said I need 2 new cats (even though 1 is new). What else could possibly be causing this, because even the old cat that came out of the truck looked fine, the truck has 126000 miles and the exhaust doesn't smell like it's burning rich (only when engine is cold). The shotgun approach to fixing this is leaving me broke.

If one is new, it should be covered under warranty. If it was installed by Nissan, parts and labor are warranted 12 months/12000 miles. If it was an aftermarket warranty, the part should be under warranty (most are typically 5 years/50000 miles).

There are several things that can cause the three-way catalyst codes, but in most cases where there are not additional codes, it is usually the converters, themselves, that are faulty. They only way to 100% confirm is to follow the diagnostic procedure in the factory service manual for those codes. If the converter has failed because it has become inefficient (most cases are due to this) rather than because the converter is restrictive or clogged, some have employed using O2 sensor spacers on the rear O2 sensors to "trick" the ECM. The spacers pull the rear sensors partially out of the exhaust stream, which alters the reading by the ECM. Spacers can be bought at places that sell performance exhuast systems and mods, or they can be made by modifying spark plug anti-foulers.

The new one isn't oem, it's from muffler express. I brought off of ebay, I'm gonna send them an email but I'm thinking I'm SOL.

I got an email from muffler express, they said it was probably a bad ignition module, or an exhaust leak or a bad after cat sensor. I'll check for an exhaust leak after work today but if it turns out the cat is some how defective I'm out shipping back to Canada and shipping to me and 10% restock fee according to thier rules. I'm starting to regret buying this truck as all I've done is spend $$$$ on it since June when I brought it, and the dealership says I'm SOL no warranty. The local Nissan dealer said that truck came in 1 year ago with P0430 and P0420 cat codes so this was obviously a long term issue. Taylorsville Automart in Taylorsville, NC will sell you junk and walk away. I will try the defouler mod that smj told me about and pray it holds up .

If the rear sensor was bad, it would usually throw a code. Exhaust leaks are easy to find, but you would have probably heard it. There really is no "ignition module" on the VQ engines. The power transistor is built into each coil pack, the crank and cam sensors signal the ECM, which "tell" the coils to fire. In essence, the ECM is sort of the "ignition module" and I highly doubt that's your problem. Coil packs and crank and cam sensors will, likewise, also "usually" trigger a trouble code. If there are no trouble codes and no exhaust leaks, there's a good chance you just got a cheap catalytic converter. I've never dealt with Muffler Express, so I can't really comment on their products. I have seen new "off-brand" and "no-name" converters cause catalyst codes soon after they've been installed. If you can't afford a genuine Nissan converter, your best bet is an established name like Bosal or Walker. If you live in California, make sure the part is CARB certified. As far as the anti-fouler med, Google it and you should find the procedure and part numbers for the anti-foulers. Spark plugs and O2 sensors use the same thread sizes (for 14mm and 18mm); the mod involves opening up the end of the anti-fouler so the O2 element can pass through. It's not a guaranteed fix, but it's a low-cost gamble as anti-foulers are only a couple of dollars and it has worked for many.

I'll take that gamble anyday, also I saw this: http://www.bigdaddiesgarage.com/straight-cel-fix.html
Seems like a high quality piece.

Looks like mufflerexpress catalytic converters are $140 paper weights, looky:
http://www.clubfrontier.org/forums/f8/b ... too-82693/

I shut off the check engine light and it hasn't been back for about 150mi. so far. Keeping fingers crossed!