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Discussion Starter · #1 · (Edited)
I recently purchased a 2006 Nissan Xterra off-road 6mt with 204k miles. Unfortunately, I had my father test drive the car and buy it for me while I was away and he did not notice that the truck has quite the stumble on acceleration and no power. The truck is throwing codes for both cats and smells like gas as well which leads me to believe the cats are the issue but a shop has told me they think this is the cause of a greater issue. I have only driven the truck maybe 40 miles as I did not want to cause greater harm.

A little more about the issue:
The vehicle starts right up every time and doesn't die once started. it seems to idle smoothly but I still notice when it's running (not exactly sure how smooth it should be as I'm coming from cammed muscle cars which vibrate a lot). The issue is that the throttle feels like it cuts out. You only notice it as an issue when you start to give it any decent amount of throttle. If you give it only a little gas it accelerates as it should and feels relatively quick. If you give it more than just a little throttle then it falls on its face and makes no power. it still accelerates but just at a snail's pace and doesn't sound quite right. The amount of throttle that causes the issue seems to be dependent on engine load but that's only a guesstimate (as in 1/4 throttle will cause the issue at 10mph but at 70mph it starts doing it at 1/2 throttle).

At first, I thought it could be an issue with the MAF but when I looked in the glove box I found an extra MAF sensor which leads me to believe it's been replaced (also the one installed looks cleaner than the rest of the engine bay). Ive also scanned for codes dozens of times and the only thing that pops up is the p0420 p0430 for the cats and p0455 for the evap.

The shop tells me they think the lack of power is caused by something else but they acknowledge that the cats are bad. My question is what else could be an issue being that no other codes are thrown? Does this sound like a case of clogged cats? or something else?
 

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P0430 / P0420 almost always means bad cats around here. That in combination with power loss, and often misfire, is one or more plugged cats. I recently learned here of a tool that allows you to measure backpressure in the exhaust. Essentially you shouldn't have any - the exhaust should be open. The primary A/F sensors are pretty easy to get to if you pull the wheel and inner fender. I am not necessarily recommending this one - just posting as an example. You might be able to get one as a tool loaner from your parts store: https://www.amazon.com/OEMTOOLS-372...sprefix=exhaust+pressure+tester,aps,90&sr=8-6

This is a very common problem around here, but it seems most mechanics that are not familiar with Nissan's misdiagnose this all the time - or that's what we notice around here.

If it is plugged cats, don't drive it - they can damage your engine.

Best of luck. Report back on what you find.
 

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Discussion Starter · #3 ·
The shop did a back pressure test and they did in fact determine the cats are bad. They still think the power issue is caused by something else. The new cats will be here at the end of the week. I'll keep this thread posted with what the solution ends up being. Hopefully, its just clogged cats. If there is anything else you think it could be caused by please let me know.
 

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‘06 Super Black S 5AT & ‘10 Knight Armor OR 5AT
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Make absolutely sure to double-triple-check and repair any fuel related engine issues before putting those cats on. You’ll fry the new ones in no time flat if running rich.

Did the shop check coils, plugs, etc? Clean the throttle body and check that new maf as well. Do a smoke test on all your vacuum lines. Etc.

There IS the possibility that the old ones just shit the bed by themselves, but best to be super cautious cause ya know, money ain’t cheap anymore…..
 
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Agree with the above. Bad cats are kinda the center of a whole engine problem universe. They do seem to just get old and go bad, which is annoying because my Toyotas never had the cats go bad after very high miles, and my 93 Ford just had it go bad last year. These ones seem more sensitive, fragile. But also, misfires will make them go bad as folks have said. Now in theory that misfire should show up as a code, which you don't have.

The other side of the universe is that, when the cats DO go bad in a catastrophic way (clogging and disintegrating), the engine can suck that debris into the chambers and grind up the cylinder walls and rings. The first symptom of this seems to be oil burning, typically.

Hopefully your story is not this drastic. If I were you I would want to just gut those primary cats and reinstall the empty shells for a while, just to establish a baseline and fix any other problems. Then when all is good, install the new cats. Or, in my case, I left them gutted. Yes, I have a code, on one side only oddly, which I am working to see if I can clear up using O2 spacers. But that's kinda another topic.
 

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One more thought. Your symptom could be consistent with a misfire OR a clogged cat. In either case you can get smooth idling and low throttle running, but with problems showing up under more load. Also, the idle of the X is certainly smoother than a cammy V8, but between the engine and mounting system it's not the smoothest I've ever felt by a long shot. So yes, you feel it when idling, just a little.
 

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@GearheadS - Just FYI, spacers don’t do squat. Been fully gutted on my ‘06 going on 4 years now. Tried the tricks and then some.
Now it’s just a cheapie reader to clear the codes whenever…..

And yeah, it seems, as so many posts over the years have shown, that our damn cats are definitely the top trouble weakness pain in the azz Xterra achilles heel money suckers of all the modern crap to deal with…..
 
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Discussion Starter · #8 ·
I appreciate all the input. it is very helpful. How often do issues arise such as misfires, vacuum leaks, and faulty throttle bodies arise without throwing a code? is that common?

While I'm quite experienced with cars, I'm a little out of my element with the computer controls as almost all of my cars have been carbureted.
 

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Yeah. A misfire is a big one and should cause codes, cascading issues that cause codes… Keep digging and you’ll get to the root of what’s going on. Just knock out each step in order while continuing to check the code reader.
I second running your “bad” cats gutted for a bit to get a baseline of what the engine is doing. Unhook the battery for 30 minutes to reset trims and start from there.

Most common misfire cause are coils, but don’t go from just my opinion.
Could be an injector, bad gas………
 

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This is all Excellent advice, and most engines won't destroy the cat unless something is amiss. Your best tool is long term fuel trims - LTFT. If you do have a vacuum leak, intermittent misfire, stuck injector or something like that, it will usually show up in your LTFT long before it throws a code. It will throw a code at +/- 25%. Perfectly running engine will be around +/-5% or less. Anything running past +/- 10% is generally considered a problem in the making.

Having said that there are several examples here of early Xterra's with plugged / imploded cats and zero other issues. I think Nissan just cheeped out on the factory cat. This is the only vehicle I have owned that I needed to replace cats.
 

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I recently purchased a 2006 Nissan Xterra off-road 6mt with 204k miles. Unfortunately, I had my father test drive the car and buy it for me while I was away and he did not notice that the truck has quite the stumble on acceleration and no power. The truck is throwing codes for both cats and smells like gas as well which leads me to believe the cats are the issue but a shop has told me they think this is the cause of a greater issue. I have only driven the truck maybe 40 miles as I did not want to cause greater harm.

A little more about the issue:
The vehicle starts right up every time and doesn't die once started. it seems to idle smoothly but I still notice when it's running (not exactly sure how smooth it should be as I'm coming from cammed muscle cars which vibrate a lot). The issue is that the throttle feels like it cuts out. You only notice it as an issue when you start to give it any decent amount of throttle. If you give it only a little gas it accelerates as it should and feels relatively quick. If you give it more than just a little throttle then it falls on its face and makes no power. it still accelerates but just at a snail's pace and doesn't sound quite right. The amount of throttle that causes the issue seems to be dependent on engine load but that's only a guesstimate (as in 1/4 throttle will cause the issue at 10mph but at 70mph it starts doing it at 1/2 throttle).

At first, I thought it could be an issue with the MAF but when I looked in the glove box I found an extra MAF sensor which leads me to believe it's been replaced (also the one installed looks cleaner than the rest of the engine bay). Ive also scanned for codes dozens of times and the only thing that pops up is the p0420 p0430 for the cats and p0455 for the evap.

The shop tells me they think the lack of power is caused by something else but they acknowledge that the cats are bad. My question is what else could be an issue being that no other codes are thrown? Does this sound like a case of clogged cats? or something else?
My 2005 pulled the same shit they tried to tell me they couldn't figure it out so I mentioned the cats and they checked and then proceeded to tell me they were shot among other things over 3000 to fix so I towed it home ordered some 300 dollar cats and swapped them myself runs great now
 

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I've had the same CAT codes on my 06 that you are getting. Haven't replaced then in three years. Every four months I dump CATACLEAN into the tank and go for a long drive. Code disappears. This may not happen with yours because it sounds a lot more serious than mine.
 

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My 2005 pulled the same shit they tried to tell me they couldn't figure it out so I mentioned the cats and they checked and then proceeded to tell me they were shot among other things over 3000 to fix so I towed it home ordered some 300 dollar cats and swapped them myself runs great now
I'm sure one of ur cats fell apart plugin up the real cat your problem sounds like mine pull the driver and passenger side o2 sensor and go for a drive it's going to be loud but if it accelerates better you have a plugged cat.
 

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Sounds similar to the issue I had with my 2006 Xterra. It would idle fine, it ran fine for awhile, but I kept getting P0430 codes, and I just put it off. Then one day, it didn't run well, misfires, loss of power, smelled gas. Got to the point where it had very little power very quickly. After reading and consulting here, I parked it, pulled the cats and one side had blown apart and lodged into the secondary cat.

I replaced my primary cats and hollowed out my secondary cats and it ran just fine!

So Cats could very well be your issue.
 

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Just take the exhaust off where it meets up with the cat if it is not welded, I have a 2000 only 2 cats. I unplugged my cats electric too so the computer would not be calculating fuel off erroneous readings from the o2 sensors
 

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Discussion Starter · #19 ·
So I replaced all 4 cats. It runs much much better but there is still an issue. It still feels slow if I get on it too much. I know its not a race car but Ive had a manual trans Xterra before and it did not feel this slow. Its intermittent and sometimes feels normal (like it should). No more smells now that the cats are fixed but the tone of the engine does still change a tad when this issue is taking place.

The issue is still lacking acceleration when giving the engine too much load. I notice it most in second gear when the truck just won't accelerate like its supposed to. My problem right now (maybe its good maybe its bad) is that the computer is throwing zero codes and the SES light is off. Hopefully it means this is not a big deal but it certainly will make pinpointing it a pain.

Being that its higher mileage and I just bought it I should start addressing maintenance items. I'm thinking fuel filter and plugs and coils.

Fuel filter is just an easy inline filter under the passenger side rear door and like $20

I found coils and iridium plugs (and intake gaskets) on amazon for $110

Last thing I can think of that may be causing an issue is possibly the throttle body and TPS. Mine is old and crusty and while its not throwing a code, whenever I hook it up to my fixd obd2 scanner (cheap little $50 bluetooth scanner) the throttle position doesn't always seem to register when I rev the engine so it makes me think that it could be an issue. Being that a remanufactured unit is only $150 I might as well replace that too.

like I said the cats definitely improved it and made the car mostly normal its still not like its supposed to be.

Anyone have any other ideas as to what could be causing these issues? Any suggestions before I just start throwing parts at it?
 

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So I replaced all 4 cats. It runs much much better but there is still an issue. It still feels slow if I get on it too much. I know its not a race car but Ive had a manual trans Xterra before and it did not feel this slow. Its intermittent and sometimes feels normal (like it should). No more smells now that the cats are fixed but the tone of the engine does still change a tad when this issue is taking place.

The issue is still lacking acceleration when giving the engine too much load. I notice it most in second gear when the truck just won't accelerate like its supposed to. My problem right now (maybe its good maybe its bad) is that the computer is throwing zero codes and the SES light is off. Hopefully it means this is not a big deal but it certainly will make pinpointing it a pain.

Being that its higher mileage and I just bought it I should start addressing maintenance items. I'm thinking fuel filter and plugs and coils.

Fuel filter is just an easy inline filter under the passenger side rear door and like $20

I found coils and iridium plugs (and intake gaskets) on amazon for $110

Last thing I can think of that may be causing an issue is possibly the throttle body and TPS. Mine is old and crusty and while its not throwing a code, whenever I hook it up to my fixd obd2 scanner (cheap little $50 bluetooth scanner) the throttle position doesn't always seem to register when I rev the engine so it makes me think that it could be an issue. Being that a remanufactured unit is only $150 I might as well replace that too.

like I said the cats definitely improved it and made the car mostly normal its still not like its supposed to be.

Anyone have any other ideas as to what could be causing these issues? Any suggestions before I just start throwing parts at it?
Hopefully you went with OEM cats (or at least Walkers) or you'll be getting to do this again soon. Seems like nobody makes any OEM replacement parts worth a crap anymore. I replaced mine with mid-grade cats off Amazon and the code never went away. Complete waste of money.
 
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