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Discussion Starter · #1 · (Edited)
Anyone already did this and can give me some advice on how to do it? I'm pretty good at working on my truck. (Done a lot harder than this) but on the two front converts it almost looks impossible to undo the bolts on the engine side because the heat shield is in the way. But at the same time it looks crazy hard to try and get that heat shield off. It's hard enough to even see the bolts on the thing. Any advice on how yall did it would help! Thanks (2005 frontier 4.0)
 

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Well, installing a replacement converter on my 1998 4-cylinder Frontier was easy-peasy after the single original one was unbolted and stolen in my driveway (I didn't need to buy replacement bolts and nuts !!). But yours sounds like a newer 6-cylinder version, you didn't state. And I'm in Arizona, you likely have more rust; so wear eye protection when under the truck.
 

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It's a bit of a PITA to replace the cats on the V6. It takes a pretty serious tool stash and/or a healthy dose of patience. You have to loosen the rest of the system first to get it off of the rear cats. Once the secondary cats are removed the primaries are much easier to access. Do yourself a favor and soak all the nuts and bolts with PB Blaster or similar for a couple days prior.
The driver's side heat shield is possible to remove intact with some super ninja wrench skills but it's nearly impossible to remove the pass side intact. Your options are to cut the shields to remove them or to work around them for the forward bolts on the primaries. It can be done, see previous mention of tools and patience ; )
 

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I had installed Doug Thorley headers on my 2006 Pathfinder, which is similar to the D40 Frontier, and then had the right side converter fail and had to replace it.
Removing the fenderwell liners is a must. Make sure you get some new, plastic, push-pins as many will break when you try to remove them; I believe there are four per side. Soaking down with rust penetrant is a must, but, you'll likely break at least a few of the heat shield bolts on the manifold. This all the more reason to install some headers! I think the only way to get the passenger side out and in without cutting it out is to undo the right motor mount and raise the engine up on the passenger side. I cut mine out using a hand-held Ingersoll-Rand air saw and cutting one piece at a time. It was a real pain! I also removed the bolt & bracket from the brake block that attached it to the frame, which allowed me to move the lines a bit. Once the shield is removed, you can get to the top bolts of the upstream converter. For the bottom bolt, you can get that from the bottom of the vehicle. Of course, don't forget to remove the air-fuel sensor. I used a Walker direct-fit catalytic converter and it worked great! I got a great deal on it for $90 from a place that sells scratch-and-dent items. Once unbolted, it can be pulled through the bottom (of course, you'll have to remove the secondary converters before that point). The left side shield can be carefully pulled through from the top once you get it unbolted. The next issue will be drilling out those broken bolts from the manifold if you plan to re-install the shields. Hmm-mmm.... Headers are starting to sound good, again! Once the heat shield and converters are removed, the headers are a piece of cake! You can get some pics of what I did here (the exhaust starts on page 2). I also replace the post-cats with Doug Thorley mid-pipes and the main muffler with a Magnaflow 12580:

http://www.thenissanpath.com/viewtopic.php?t=12841&postdays=0&postorder=asc&start=0
 

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If you have a sizable compressor get a cut off wheel tool with extension.
ex: http://www.harborfreight.com/air-tools/specialty-air-tools/3-in-high-speed-extended-reach-air-cutoff-tool-67996.html[/URL]

front flange of cat has 3 bolts. I think 2 are in same direction and can be cut off as new cat will have these 2 bolts at flange. Once they are cut off it becomes easy.
Just look at what your replacing and make sure to cut the right bolts off.

Also you will need about 2 1/2 ft of extension and some swivels to use with a socket. Once you have the extensions in hand you will need to be creative running them to the bolts.
 

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I did mine a few months ago. I didn't have to cut any bolts or use a impact wrench. Make sure you soak all bolts with PB blaster in advance multiple times. This job requires patience and breaker bars. I replaced both front cats with walkers and denso o2 sensors. It's been 5k and so far so good.
 

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I replaced the forward catalytic convertor on the passenger side of my wife's 2006 Xterra. There was no way to remove the heat shield (for the exhaust manifold) in one piece. You probably could, but that would require the removal of some coolant line above.

I ended up cutting the heat shield, as well as prying it and smashing it.

You will need to remove all hanger bolts for the exhaust manifold, as well as loosening the bolts on the opposite bank catalytic convertor. I then used a ratchet tie down to pull the exhaust system to the rear of the car.

Be sure to use new exhaust gaskets as well.
 
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