[RLee]

I've been looking through posts to get my 2011 Xterra up and running but now I'm stuck and hoping someone with a little more knowledge might be able to help. The X had a misfire in cylinder 2 (cut cable to the coil pack) and basically burned out the cats on bank 2. I fixed the wire, new fuel injector, coil pack, o2 sensors on bank 2, cats for bank 2, and a new intake sensor since it was throwing a code for it.

Everything seems to be working good and all the original codes have cleared except now I have a P0430 code and bad gas mileage (about 12mpg). The cats I put in are Easter Catalytic which seemed like a good buy, could I have got bad cats? Compression in all the cylinders were at or above 175 psi.

I have some screen shots for the sensors while idling and driving freeway, the fuel trim is moving around for bank 2 more than I think it should. Does the downstream o2 sensor have an input on the fuel trim?

I'm at a loss and don't want to just throw more parts at it, any ideas?

 

[Lowcountry idn]

If I had to guess, I would guess the same thing that gummed up your cat gummed up your primary A/F sensor. The lamda value should be around 0.45V, but I have found every reader likes to display that differently for some reason.

I see your STFT but there mostly irrelevant. What are your long term fuel trims at?

 

[mtnbound]

Sounds like you did all the right stuff, I highly doubt that the eastern cat was bad, but anything is possilbe, or maybe one of the new o2 sensors isnt doing its job well?

how the F did a cable get cut? were you doing some other work and that was collateral damage?

 

[RLee]

My primary A/F sensor is new as well, my LTFT is the same for both banks, it sits right about 5%.

I don't know how it got cut, it was like that when I bought it. The price was right and I figured I could fix it, I'm much better with the mechanical stuff but once it comes to electronics and sensors I'm not so good. It barely moved enough to get it onto the trailer when I bought it, the bank two cat was that plugged up. I went on a limb thinking the downstream O2 sensor might have been bad and already swapped that and I still have the same results, these readings were from the 2nd new O2 sensor.

I'm still not sure what could be causing my STFT to bounce around like that, as far as I know the downstream O2 sensor doesn't affect it and it should be going off the A/F sensor. Again, all these sensors are not my strong suit so correct me if I'm wrong.

 

[Lowcountry idn]

My primary A/F sensor is new as well, my LTFT is the same for both banks, it sits right about 5%.

I don't know how it got cut, it was like that when I bought it. The price was right and I figured I could fix it, I'm much better with the mechanical stuff but once it comes to electronics and sensors I'm not so good. It barely moved enough to get it onto the trailer when I bought it, the bank two cat was that plugged up. I went on a limb thinking the downstream O2 sensor might have been bad and already swapped that and I still have the same results, these readings were from the 2nd new O2 sensor.

I'm still not sure what could be causing my STFT to bounce around like that, as far as I know the downstream O2 sensor doesn't affect it and it should be going off the A/F sensor. Again, all these sensors are not my strong suit so correct me if I'm wrong.

Sorry, I missed the new A/F sensor.

If the LTFT is at 5% then everything in fuel delivery and burn is working correctly, at least according to the sensors. Your STFT is supposed to bounce around. There almost meaningless as a diagnostic tool. If there not bouncing around be worried - there there to adjust immediate problems - like fuel inconsistencies for example. They are actually the input into the LTFT - ie if the STFT is always running 5% positive for example, the ECU will push the LTFT up 5% and drop the STFT back to zero.

So the secondary 02 sensor has no input into engine control from everything I have read - it just monitors efficiency - but it could be your P0430 cause. It is also possible you got a bad cat. Easterns have been pretty good, but quality control in everything lately has been crap. I had 3 out of 6 General tires out of round. A warranty replacement for an earlier warranty replacement for out of round, was also out of round. So I guess never assume. The problem is - there is no good way to test a cat.

Also the mileage concerns me. Over how many miles is that average?

Also - the sensors were name brand - not house brand or ebay?

 

[RLee]

I've driven it about 500 miles since I got it, 130k miles total. Everything I replaced is OEM brand name except for the cats.

This screen is what has me a little confused, I wish the graph was better but my bank 2 A/F voltage is bouncing around with the STFT where bank 1 is steady for both. Am I still having a mechanical problem or is my A/F reading correctly? It would make sense if the O2 sensor had an input but that's where I'm confused.

 

[Lowcountry idn]

Yes, so that is not good. Thats your 02 equivalence ratio. It should sit right at 1 (0.98 to 1.02 is generally considered acceptable) Since its only 1 side, its got to be something directly in that bank - 02 sensor, injector, etc?

What OBD reader are you using BTW? I like the way it plots those.

 

[RLee]

I'll have to dig around and see if one of the cylinders is having problems still. I'm using Torque Pro on my phone, the adapter I'm using is the Obdlink MX+. It's not the most user friendly but once you get it set up it works. The app that comes with the adapter isn't bad but I've been using Torque Pro for a while now and mostly have it figured out.

 

[westslope]

@RLee: I also like the way you are displaying information with Torque Pro. Makes me think that I need to take a closer look at display options in Torque Pro.

I am surprised that you are using OBDLink MX+ as opposed to OBDLink LX which is what I have. What can MX+ do that LX cannot do? Transmission fluid temperatures?

My own personal 'cat' saga.... The X is currently in the Nissan dealership where they are (with some difficulty) installing primary AP Eastern catalytic converters, rear OE O2 sensors and replacing any parts of the exhaust system that should be replaced.

The tech noted that there was a pin-hole in one of the cat welds. He also noted considerable difficulty get the rear of these primary cats to fit the exhaust tube (or whatever you call it). The X is likely with a muffler exhaust speciality shop to do some bending, fitting and welding. On the bright side, the service manager is very forthcoming, and when this is all finished, I hope to drive away with a functioning exhaust system, no codes and a decent short-term warranty for the labour (but obviously not the parts I supplied).

Lowcountry idn has documented at length his own personal difficulties in getting the AP Eastern cats to fit. I chose AP Eastern cats from Rockauto.com because a single OE cat up here costs ~C$900 (ouch!) and I failed to find an aftermarket cat with fewer issues than the AP Easterns.

All this to say, that any leaks in the exhaust system may be causing you problems. I reckon that exhaust leaks can be rather difficult to identify if one is working from 6-tonne jack stands. Even if one is working on a hydraulic lift, it still takes two to do this.

Good luck and please keep us informed of your progress.

 

[Lowcountry idn]

Yes, my Easterns fit like crap. I did get them to seal with the help of some really good gaskets, but now the geometry is such that there almost sitting on the crossmember and rattle against it with most every pothole. I have tried loosening them off and manipulating them away from it, but it lasts about a week then moves itself back to that position. I am getting close to the mileage where i expect codes to come back, so I am debating my next move.

Still, I don't think a leak would cause a P0430. If the exhaust were leaking it would make the emissions at the second 02 sensor, better not worse, wouldn't it?

 

[RLee]

I had the baseline MX for years before it failed so I just went with the MX+ because it was similar. I'm not worried about the new one failing because my first one was not a production model, my brother works for the place that makes them and gave it to me to evaluate it when they were first hitting the market.

I didn't have a problem with the fit or leaks as far as I can tell, I got the direct fit and it bolted up exactly.

More Information for AP / EASTERN 644091

I think my next step is to disconnect the downstream O2 sensor and see if that affects my fuel trim, I tried I'm plugging fuel injectors and coils to see what the sensors read and my fluctuations went away. That might be a sign of a bad cat because it's no longer having to work as hard because not as much exhaust is coming through with a cylinder not getting fuel. That also leveled out the a/f bumps I was getting, if I pull the O2 sensor and the variations in my a/f and STFT go away I might have just got a bad cat. At least this time it's going to be way easier to take off because everything's not going to be rusted tight.

I think I did read somewhere that an exhaust leak before the sensor might be allowing some air in which would throw off the O2 sensor, I just don't know how big the hole would have to be.

 

[General_Tarfun]

@RLee: I also like the way you are displaying information with Torque Pro. Makes me think that I need to take a closer look at display options in Torque Pro.

I am surprised that you are using OBDLink MX+ as opposed to OBDLink LX which is what I have. What can MX+ do that LX cannot do? Transmission fluid temperatures?

My own personal 'cat' saga.... The X is currently in the Nissan dealership where they are (with some difficulty) installing primary AP Eastern catalytic converters, rear OE O2 sensors and replacing any parts of the exhaust system that should be replaced.

The tech noted that there was a pin-hole in one of the cat welds. He also noted considerable difficulty get the rear of these primary cats to fit the exhaust tube (or whatever you call it). The X is likely with a muffler exhaust speciality shop to do some bending, fitting and welding. On the bright side, the service manager is very forthcoming, and when this is all finished, I hope to drive away with a functioning exhaust system, no codes and a decent short-term warranty for the labour (but obviously not the parts I supplied).

Lowcountry idn has documented at length his own personal difficulties in getting the AP Eastern cats to fit. I chose AP Eastern cats from Rockauto.com because a single OE cat up here costs ~C$900 (ouch!) and I failed to find an aftermarket cat with fewer issues than the AP Easterns.

All this to say, that any leaks in the exhaust system may be causing you problems. I reckon that exhaust leaks can be rather difficult to identify if one is working from 6-tonne jack stands. Even if one is working on a hydraulic lift, it still takes two to do this.

Good luck and please keep us informed of your progress.

I’m surprised you were able to get a dealer to install aftermarket parts, especially the cats which are prone to issues if they’re not OE.

 

[westslope]

I’m surprised you were able to get a dealer to install aftermarket parts, especially the cats which are prone to issues if they’re not OE.

So am I. I have a good relationship with the Nissan dealership parts manager. I asked him for a recommendation for a muffler shop. He recommended their own shop.

At this point I have mixed feelings. The dealership sent my X to a muffler shop to weld the pin-hole, make adjustments and, as it turned out, to replace the muffler and rear pipe. The muffler shop's estimate for some of this work was half of what Nissan would charge so the service manager at Nissan requested the muffler shop do it.

Should be ready by Tuesday. Looking at a bill close to C$2K. Which is just fine by me.

Here is the optimistic take: the dealership may not have been as well equipped to do this admittedly difficult job as a really good muffler-exhaust shop. But the dealership likely understands better than most how the whole system fits together so having the dealership as the master contractor could work to my benefit.

So far I am quite happy with the way the Nissan service manager -- probably the most stressful job at the dealership -- has kept me informed of difficulties, challenges, options and progress. If I require something specialized or difficult to do in the future, at this point I would not hesitate to have this dealership service shop do it fully understanding that it will cost.

 

[RLee]

After more headache I'm going to try and get a new converter under warranty, they are asking for the sensor readings so hopefully they can tell if it is their cat. I'll update when they reply back or send a new one.

 

[RLee]

I just realized I never updated this, got the cat replaced under warranty. I might have gotten a bad cat and bad A/F sensor together since I got a CEL for the sensor after replacing the cat. Sensor replaced under warranty too and the light went away and hasn't come back, it's been a couple months now. I always hate seeing threads like this where you don't know if the problem ever got fixed!

 

[mtnbound]

its pretty common for the o2 to go bad after the cat is replaced. happened twice for me, once on each bank!

 

[RLee]

its pretty common for the o2 to go bad after the cat is replaced. happened twice for me, once on each bank!

The O2 was fine, upstream was the problem. When I swapped the cats I got all new sensors.

 

[mtnbound]

The O2 was fine, upstream was the problem. When I swapped the cats I got all new sensors.

i am referring to the up stream or primary. people seem to call them o2 or af depending on who you ask. ive always called them o2's. maybe im wrong. the part i installed is labeled air fuels sensor so i guess your right.