P0420 on a 2005 G35Sedan with 266K Miles

[cfauvel]

So far this has popped just once.

But, based from what I've read, it points to the actual cat itself...and I guess bank 1 means the starboard side of the engine (passenger in USA markets).

Various forums suggest looking for exhaust leaks, and will do some smoke tests and report back.

But assuming IT IS the cat, who do you recommend for replacement cats? I really don't want to throw OEM priced cats (or Magnaflow priced cats) at this car.

I found ("Kinetix Racing High Flow Cats HFC, Smog Legal VQ35DE - Nissan 350Z / Infiniti G35") cats on Concept Z for about $419 for the pair. Scared to go with the cheaper ones on Ebay.

Thoughts or recommendations?

[AZhitman]

Sorry this took a while to answer... Definitely steer clear of the cheapo cats.

Have you a replaced the oxygen sensor on Bank 1? I'd do that first. If it is indeed the cat, you may as well do both since they're the same age.

[cfauvel]

I haven't replaced the O2 sensor yet...the code hasn't come back since I posted the error...

[zypor]

I'm not sure what you mean the code hasn't come back. Did the code clear on its own or did you use a code reader and clear the code?
Very Very unlikely it's the O2 sensor. In the FSM there is a long list of items to check. On the intake side look for leaks, exhaust leakage only joints just upstream of the downstream (NUMBER 2) O2 sensor. You can check for leak by running the engine and have someone plug up the exhaust at the tailpipe then look for leaks at the joints. The reason I say look for leaks at the joint just upstream of the downstream O2 sensor is if there is a leak this will effect the voltage on the downstream O2 sensor and give you a check engine. Also you can check for proper spark plug operation, check fuel injectors for leakage and you can check the O2 sensor by using a volt meter and reading voltage at the ECM for the O2 sensor. The cleaners sold probably won't work there is a lacquer thinner procedure that people have used with some success.

[cfauvel]

Hey zypor,

yes I cleared the code and it didn't come back ....for a long time.....It came back later on and I did a cat cleaner again and cleared the code again....I am at 273K.

The fuel trims are not right at all (searching for the numbers), especially on bank 1.
AI pointed me to bank 1 upstream O2 sensor as I got these numbers via LIVE data at about 40mph
They mentioned all of the things you mentioned too....I don't think it is intake leak as that would affect both banks...exhaust leak COULD very well be it.

Ok so the voltages
O2s11 = 0.295 v
O2S12 = 0/730 v
O2s21 = 0.590 v
O2S22 = 0.690 v

Fuel trim at around the same speed
SHRTFT1 = 0.8 %
LongFt1 = 10.2 %
Shrtft2 = 0.8 %
LongFT2 = 7.8 %

Then at another time on the same trip I got these numbers for fuel trims
SHRTFT1 = 1.6 %
LongFt1 = 10.2 %
Shrtft2 = -3.9 %
LongFT2 = 7.8 %

Then on same trip a little but later I got
VSS = 33.55 mph
MAF = .03 lb/s
O2S11 = 0.286 V
O2S12 = 0.680 v
O2S21 = 0.580 V
O2s22 = 0.680 V

Then AGAIN on same trip a little but later I got
VSS = 34.88 mph
MAF = .03 lb/s
O2S11 = 0.285 V
O2S12 = 0.680 v
O2S21 = 0.630 V
O2s22 = 0.440 V

I'm not any good at reading these numbers, but from what I understand the higher fuel trim % means the ECM THINKS it is running lean and needs more fuel? We definitely have seen less MPG over the years

AI stated that since bank 1 upstream voltage isn't changing much that something is wrong there.

I feel that there might be two issues...the bank 1 o2 and the injectors are tired and/or clogged, or the injectors are just not atomizing the fuel well and coming out as a stream.
I do have new hitachi injectors that I was going to put into my 350z, but maybe I should put them into wifey's G35 instead.

What do you think of the numbers?

[zypor]

Normal % is + or - 10 and you're not far off. Because it's only on Bank 1 the fuel injectors need to be looked at. Before taking them out you may want to try a fuel injector cleaner BG MK44 gets good reviews. All in All your cat may still need to be replaced but it's nice to find out what caused it to fail in the first place. from the data the snapshot of the O2 voltage is hard to determine . The downstream O2 sensor voltage should read high .6-.7v and be fairly steady or may be higher this indicates the oxygen is being consumed. The upstream O2 sensor will move between .1 and .9 volts as it sends signal to ECM to adjust fuel mixture. The ratio between the two should be .75 or less. I would try getting the injector cleaner first. O2 sensor will run about $70 Denso makes a quality sensor. If you can get a live reading of the sensor over time this will give you a better understanding of what is going on. You can monitor the sensor Voltage with a voltmeter at the ECM. As always when reading sensors make sure engine is at normal operating temps the CAT needs to completely warmed up.

[cfauvel]

Thanks Zypor,
the snapshots I gave were whilst my wife was driving....I can do the same PIDS and capture a video instead if that helps....it seems like the O2 upstream on bank 1 isn't swaying much at all. Could be an exhaust leak. I am going to try to stick my smoke machine into the tailpipe to see if I can see smoke coming out of the exhaust connecting points....if that doesn't work I'll try to use the smoke machine at the O2 downtream bung as that is easier to get to ....I'm hopeful that the smoke can permeate through the cat and show any exhaust leaks...other than that I have no other ideas to flesh out an exhaust leak near the upstream O2 sensor on bank 1.

I would have expected the MAF value to change too a bit, no?

I have a new Denso O2 upstream sensor for bank 1 and new hitachi MAF sensor too.

One time I captured the summation of the short term and long term % on bank 1 in the 14% range....just didn't capture it here.

[VStar650CL]

Your '05 G doesn't have O2's in front, it has wideband A/F's centered at 1.5V (lower is rich, higher is lean). They don't "swing" like an HO2S unless the ECM makes them swing, and you'll only see large movements when you're on and off the throttle. In a cruise the swings will be tiny, so your O2S1 readings don't make any sense at all. That 0.295V implies you're running 11.5:1 mixture, which is impossible with a normal STFT. I think your scanner must be giving you artifactual data for the fronts. BTW, your STFT's and LTFT's are all well within the normal range, I doubt you have any issues there.

That all said, the only way to tell anything from your rear O2's is to graph them. Spot voltages tell you nothing. The ECM judges the health of the cat by the timing between swings and the health of the sensor by the minimum and maximum voltages of the swings, so without being able to see the timing you can't tell anything about the cat, and without being able to measure the amplitude you can't tell anything about the sensor.

The bottom line I see here is that since Cataclean helped for awhile, your cat is probably just getting weak in old age. Successive applications will just work for shorter and shorter times until finally it dies and the P0420 won't go away.

[cfauvel]

yes VStar650CL you are correct that the upstream doodads are not O2 sensors, but A/F sensors...as layman I just use that term. Indeed seeing a screen shot is probably not the most helpful, I get what you are saying. I think my scanner can graph those pids, not sure if I can offload the results though....I'll re-do the test and video the graph and see if I can offload the graph for all to see.

I'll re-do the tests graphing the rears solely, the fronts soley, then both together. I'll keep you posted.

I too think the CATs are just old, but also suspect the injectors since both have 273K miles on them. My Z has 203K miles

Any recommendations for replacement cats? I am not going to spend 1K+ on new oem cats.....the car is worth $1,800 now according to Kelly Blue Book....She still looks good and got a new transmission rebuild at around 230K.

[VStar650CL]

If the injectors were actually problematic you'd be running fuel trims that were out of whack. Leaky injectors would cause big minus numbers, clogged ones would cause big plus. Yours are very normal. For reference, the max STFT or LTFT is +/-25%, that's where you get lean or rich codes. Your LTFT's show slightly lean (plus), but that could be from any number of harmless things. Run some injector cleaner through it, calibrate your MAF, and call it good.

You don't run much risk of cat inhalation on a longitudinal VQ like you do on a transverse, so on a car with that many miles, I won't steer you away from a cheap cat. I wouldn't go EBay, but you can get a decent Davico on RockAuto for about $250 or a better AP/Eastern for about $440 (unless you're in Cali, CARB is different).