Hey guys, I’ve been looking into replacing my upstream cats and deleting my downstream cats. I’ve seen some other threads about doing this, but it always seems to end up with the Cali emissions hoopla and some mixed reviews of replacement cats. I’m from Arkansas, and until I see them bringing their machine down my driveway to test my exhaust I’m not gonna worry about how compliant it is. I have just recently got my trans replaced (previous owner didn’t plug in a vacuum hose and it’s sucked dirt since I’ve owned it) and the mechanic said that I had a considerable amount of back pressure, most likely from my cats. That was 2 weeks ago, and just 3 days ago I’ve had the SES light come on, which ended up being a P2A03 code, meaning I have an exhaust leak or one of my O2 sensors are bad. What I wanted to do is have all 4 cats removed, and have them replaced by 2 thunderbolt cats from eBay (I’ve read about them and I plan on using them on other stuff as well, they seem to have a good track record and people like them for a cheap hi-flow), of corse having a new pipe for both sides be fabricated so they’ll bolt to the manifolds. I’d also want to put spacers on the back 2 O2 sensors. Would something like this work or is there a different route that would be better/ cheaper? I figure the two cats are around $100 for both, plus the muffler shop I have in mind does good work for a reasonable price, but I haven’t contacted them yet.
Cat Delete and Replacement
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The rear cats are not monitored by the system so there's no need for them really, as far as the computer goes. The common thought is that they were put there for redundancy, to catch any pollutants that make it past the primaries. The o2 sensors are before and after the primaries, nothing downstream of the secondaries. My Xterra came with gutted cats but I was getting codes for both so I replaced them with aftermarket cats. Probably could have just replaced the o2 sensors and been done with it, but I didn't know I had gutted cats until I pulled them off.
For the P2A03, you're correct it's usually a leak - I've seen a few guys have this code pop up after replacing their primaries and 9/10 times it's due to a crappy flange gasket that came with the cats. I'm going through this now, which really sucks considering how much of a pain in the ass it is to remove the cats. It's not difficult work but access to the cats is terrible and drives me nuts.
For the P2A03, you're correct it's usually a leak - I've seen a few guys have this code pop up after replacing their primaries and 9/10 times it's due to a crappy flange gasket that came with the cats. I'm going through this now, which really sucks considering how much of a pain in the ass it is to remove the cats. It's not difficult work but access to the cats is terrible and drives me nuts.
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I've had good luck with having all the cats deleted, a magna flow muffler and a 12" resonator. Been about 1200 miles with no cats and the X is running better than ever.
That’s why I was thinking about deleting them, just because I knew there wasn’t much room at all in there to get too them. I hope it’s a leak, I just looked under it and it looks terrible, stuffs rusted together and one of the studs are broke on my downstream, and it’s been welded on.
That would be a cheaper alternative just going with a straight pipe. What did you do for your O2 sensors, did you just put spacers on the lower 2?
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The 02 sensors stayed, I just deleted the cats. Check engine light is on, cat codes for both sides
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I had a P2A03 code and based on advice here I went looking for a leak - and I did find a cracked flange on the front of the secondary cat so I replaced it - but the code came back immediately. I then replaced the primary 02 sensor and it solved the problem. So based on my sample of 1, I would suggest replacing the sensor first - with a Denso since that is what my OEM one was. Its cheap an easy - and you can go from there.
I also suggest attempting to get the code solved before you start changing a bunch of other stuff. My experience is that making a bunch of changes with a problem makes it harder to solve if that doesn't fix your problem. One thing at a time in steps is my philosophy.
I also suggest attempting to get the code solved before you start changing a bunch of other stuff. My experience is that making a bunch of changes with a problem makes it harder to solve if that doesn't fix your problem. One thing at a time in steps is my philosophy.
Ah I see, well maybe I can find a way to get my SES to go out
Yeah I need to get my code to stop before I continue, I just figured I’ll need to do something since that guy told me they seemed to be clogged. I planned on getting them checked at the muffler shop just to be certain. The downstream left denso O2 sensor is $56 on rockauto, with the other 3 being $80. Is that what you paid roughly? And could you tell which one was out or did you just start replacing them? I’m fine doing one for $56/$80, I just don’t want be replacing 3 for that price when it was just one that was bad.
Really the spacers would be redundant if I put cats back on it (which I’m thinking more of just going with a straight pipe) just to make sure the downstream O2 sensors wouldn’t have a fit since they were different than stock.
Would putting spacers on the two downstream sensors trick them into thinking everything was fine even if I went with a straight pipe?
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A P2A03 code would likely be the upstream sensor unless the www is wrong. I changed the primary sensor to solve my issue - the one upstream of the first cat -
P2A03 NISSAN - Air Fuel Ratio Sensor Circuit Range/Performance Bank 2 Sensor 1
You didn't mention what year your X is - however earlier models - I think 2005 and 2006, had an actual 02 sensor upsteam, and then they went to A/F sensors in I think 2007? Both upstream sensors are the same, as would be both downstream sensors. My 2008 uses a Denso 234-9038 Air Fuel Sensor upstream - but as I mentioned they changed by year so follow the catalog. And shop around by part number - because with shipping rock auto is often not the cheapest anymore.
Oh - and if you do think your primary cats are plugged best not to leave it. You can pull the secondary cats and have a look. Often the primary cat will implode and send crap downstream to plug the secondary - and you DO NOT want to drive it like that - several around here have wrecked their engine doing so.
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admission that federal law do not trump state law?
Yeah, I didn’t think nothing of saying that to begin with, mines a 2010. I just got back from the muffler shop and looks like I dodged a bullet. He checked my two upstream cats and they’re both fine, just the only problem was my drivers side was dumping fuel, so looks like I just need to change out my A/F sensor.
Here in Arkansas no one cares, there’s so many people that run without them. Plus there’s no sort of a state inspection, so I’m good. Yeah if I went off somewhere I could be inspected but I’m not worried about it. Plus with it being hopefully just the A/F sensor I’ll be able to put the new exhaust on hold.
I did, however, find another possible way of going about it: I’ve heard on some of the other discussions that people were able to solve the code issue by using uprev, is that a sure fire way of solving the SES because of that code? Really this is for future reference, again I hope it’s just the sensor
Well, so far so good, after I replaced both A/F sensors and reset the codes, the SES light has stayed off.
For curiosity’s sake, has anyone done a full 4 cat delete and used uprev to cover the code plus the lack in power some people report from deleting the front 2 cats?
For curiosity’s sake, has anyone done a full 4 cat delete and used uprev to cover the code plus the lack in power some people report from deleting the front 2 cats?
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Full cat delete (all 4), magna flow muffler and a 12" resonator for sound. Runs better than ever now. I feel I gained power. Not sure why people say they lost power.
Yeah I’ve heard of some people getting less power w/o any cats, but others say they got more w/o em. Have you seen a drop in fuel economy since you did the delete?
Also, as an update the SES light has come back on with the same code, just this time on the other bank (passenger side). I’ve started to notice a pretty loud hissing sound from the back of the intake/ FI unit, so I might have a vacuum leak that’s causing it. Didn’t notice it before now.
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I have not seen a drastic change in fuel, but my daily commutes are just a few miles. The only time my X gets real mileage is when I go offroading ( so it's hard to tell, due to terrain and 4wheel drive)
Well after letting it set a while during the summer, then letting my grandpa use it after he sold his pickup, the SES light has mysteriously turned off, and I have since seen an increase in gas mileage back to around 18-19 commuting to college which is how much it was getting before the SES light came on. Why it went out is beyond me, maybe the MAF sensor had something stuck to it, but grandpa said “your welcome for fixing your car” all the same lol
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I went with Doug Thorleys, but be warned - they'll make your Xterra sound like actual garbage. I'm going to be taking mine off and reinstalling the originals as soon as I get enough motivation.
I stumbled on the "B pipes" awhile ago and noticed that in Nissan oem parts exploded views the "downstream cats" are called EXHAUST TUBES. Less than 1/2 the price of the actual cats and no heat shields.
As far as I know, the downstream O2 sensors are always after the last cat to report on cat efficiency.
Are we 100% certain that the "downstream cats" after the second O2 sensor aren't resonators? A resonator makes a lot more sense when you consider how its normally done and the above mentioned garbage exhaust sound.
As far as I know, the downstream O2 sensors are always after the last cat to report on cat efficiency.
Are we 100% certain that the "downstream cats" after the second O2 sensor aren't resonators? A resonator makes a lot more sense when you consider how its normally done and the above mentioned garbage exhaust sound.
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