Am I in danger f damaging anything if i just leave it?

[dared3vil00]

So, as some of you may know i made a thread about how i got the SES and code that my cats are done. I took it to a friendly dealer who confirmed it was a code for bad cats, and they erased the code. That was almost a month ago now. The SES light has stayed off (knock on wood) and i'm not sure what to do. I have heard horror stories of what not replacing cats can do (racerzx for one) and I am wondering IF the SES light stays off, am i ok NOT to replace the cats? Thanks

[Baedarlboo]

Sometimes, that code could be triggered by a failing 02 sensor also....but if it's been over a couple hundred miles since reset and it hasn't come back, I wouldn't worry about it too much.

[hfrez]

If the light comes back several times I would start getting concerned but if it stays off you are good to go. If the problem persists the light will most definitely come back. Just because they erased it doesn't mean the computer will continuously ignore the problem.

[dared3vil00]

Yeah i thought it wouldn't just ignore the problem, However i was curious if it required some attention, which thankfully it appears it doesn't.

[eieio]

it'd be nice to be able to verify that the "cats" are OK
sometimes a bad cat can cause engine damage............
http://www.thenissanpath.com/viewtopic. ... cat+damage

[skwerl]

Article on how to diagnose bad cats:
http://answers.yahoo.com/question/index ... 830AAzOPz0


The front cats are the two to be concerned with (there are 4 total) but the front two cats are between two O2 sensors. FYI, Advance Auto and Auto Zone are no help. Advance was going to sell me a rear cat and it wasn't labeled front or rear. When I asked them why that seemed to be the part # to the rear cat made by Walker they just told me they were sorry they had no more information.

Walker, Eastern Catalytic, and Davico are three reasonably priced brands I've been able to find (Magnaflow are expensive).

Here are links to front and rear cats from the Walker website and a few links to buy the cats. I would make damn sure my O2 sensors were all good, have my plugs replaced, and check for vacuum leaks before putting cats on. One way to check if a cat is functioning is to point an infrared thermometer on the front of the primary cat and on the rear of the primary cat and their should be about 100 degree difference in temp.

Front Driver
http://catalog.walkerexhaust.com/catalo ... tus=ACTIVE

Front Passenger
http://catalog.walkerexhaust.com/catalo ... tus=ACTIVE

Rear Driver
http://catalog.walkerexhaust.com/catalo ... tus=ACTIVE

Rear Passenger
http://catalog.walkerexhaust.com/catalo ... tus=ACTIVE



These Davico are the cheapest I've found from a reputable dealer:

Davico Front, Driver Side Catalytic Converter
http://www.autopartswarehouse.com/sku/N ... 18218.html

Davico Front, Passenger Side Catalytic Converter
http://www.autopartswarehouse.com/sku/N ... 18219.html



Eastern Front, Driver Side Catalytic Converter
http://www.autopartswarehouse.com/sku/N ... 40710.html

Eastern Front, Passenger Side Catalytic Converter
http://www.autopartswarehouse.com/sku/N ... 40711.html





Here's a site that also sells Walker cats (cheapest on Walker rear cats):

Front Driver
http://www.woodys-auto-supply.com/auto- ... =WAL-16468

Front Passenger
http://www.woodys-auto-supply.com/auto- ... =WAL-16467

Rear Driver
http://www.woodys-auto-supply.com/auto- ... =WAL-16400

Rear Passenger
http://www.woodys-auto-supply.com/auto- ... =WAL-16399


Article on how to diagnose O2 sensor problems:
http://www.aa1car.com/library/o2sensor.htm

A good O2 sensor should produce an oscillating waveform at idle that makes voltage transitions from near minimum (0.1 v) to near maximum (0.9v). Making the fuel mixture artificially rich by feeding propane into the intake manifold should cause the sensor to respond almost immediately (within 100 milliseconds) and go to maximum (0.9v) output. Creating a lean mixture by opening a vacuum line should cause the sensor output to drop to its minimum (0.1v) value. If the sensor does not flip-flop back and forth quickly enough, it may indicate a need for replacement.

My issue is my primary cats both show the 100 degree difference between front and rear leading me to believe one or more of my O2 sensors are bad but there are specific codes for bad O2 sensors which I'm not seeing leading me to believe I have a bad cat. It's a very tricky thing to diagnose if you don't know what you're doing. I wouldn't even know where to begin to hook up an oscilloscope like recommended in the article above.

I bought an OBD II code reader/diagnosis tool to record readings from my O2 sensors and this is what I saw. I was parked and gave throttle up to about 3k~4k RPM and back down to idle repeatedly for about 30 seconds and this is the readings of my O2 sensors.










If I'm reading this correctly, Sensor 1 bank 1 (drivers front O2) and Sensor 2 bank 1 (drivers rear O2) have bad readings.
To add to my confusion is I believe if the ECM senses that the motor is running too rich in the case of a bad cat, the ECM will lean out the air/fuel ratio which would also affect the readings of the O2 sensors. That seems to me to make it even harder to tell whether an O2 sensor or cat is bad when the O2 sensors could be self-adjusting for a bad cat.

Furthermore, my vehicle gets the same MPG it has always gotten and doesn't run poorly or idle roughly. I sold the vehicle anyway so good riddance Nissan!

[deermjd]

Good info! Thanks for doing all that research. Sorry to hear you sold your Pathfinder. Was it having any problems other that the cats?

[skwerl]

Good info! Thanks for doing all that research. Sorry to hear you sold your Pathfinder. Was it having any problems other that the cats?

I had to replace the fuel sending unit since it was right over the mileage limit Nissan extended. About $100 and half a day so it was child's play compared to this cat issue.

[disallow]

On the Cats, not sure if anyone has mentioned, but RacerZX had an issue on his V6... IIRC there is a potential to get pieces of the catalyst upstream and into the cylinders. If that happened, you could have major engine damage.

Not sure where you live, but if its not in the cards to replace them, I would find someone handy with a welder and cut them out. You'd then have to live with the constant SES light, but at least you wouldn't damage them.

This all assumes, of course, that it is your Cats that are bad, and not just the O2 sensors.

[skwerl]

On the Cats, not sure if anyone has mentioned, but RacerZX had an issue on his V6... IIRC there is a potential to get pieces of the catalyst upstream and into the cylinders. If that happened, you could have major engine damage.

Not sure where you live, but if its not in the cards to replace them, I would find someone handy with a welder and cut them out. You'd then have to live with the constant SES light, but at least you wouldn't damage them.

This all assumes, of course, that it is your Cats that are bad, and not just the O2 sensors.

You've got that right. Even if you don't want to cut them out and have to spend ~$500 on cats is better than ruining a motor! Cut the back cats off if you don't want to spend that cash. I would make damn sure anything was bad before I replaced it. There are some cat inspection tips on one of the links I posted.

[RacerZX]

There's no way for cat chunks to get up into the cylinders, but the back pressure caused by a failed cat can cause detonation which can be a bad thing.

Have you tried just whacking the cat with a rubber mallet? If you hear rocks inside instead of a solid thunk, that's bad...

[disallow]

hmmm I guess IDNRC...

[smj999smj]

There's no way for cat chunks to get up into the cylinders, but the back pressure caused by a failed cat can cause detonation which can be a bad thing.

Have you tried just whacking the cat with a rubber mallet? If you hear rocks inside instead of a solid thunk, that's bad...

"Chunks" may not be able to get up there, part small bits and particles from the catalyst media certainly can. The issue is similar to the QR25DE in the 02-04 Altimas and Sentras, which, like are VQ40DE's, do not use a conventional EGR system (EGR valve, pipe, solenoid valve, etc.). The accomplish EGR by partially opening the exhaust valve during the intake stroke to suck exhaust back into the combustion chamber, which is made possible with the variable valve timing. The small particulate from the catalyst is very abrasive, which scores the cylinder walls. At least that's what the guys on Nissan's tech hotline were telling their technicians a few years back.