halakar

Hey guys. I own a 2002 Maxima SE 6MT that has been running ****ty for a long time. Just clicked over 200K. I am no VQ35DE guru, more of an SR20 man personally.

I love my car, I've had it for 3 years now but as of late it's been running ****ty. P0138 code for rear bank1 o2 and P0430 Catalyst TW. As of late, **** poor performance, no power. Seafoamed it, changed out the plugs and ignition coils, rocker cover gaskets, cleaned throttle body and MAF, car ran even worse afterwards, bucking and hesitating. Threw my hands up and took it to the dealership. $440 later, they swapped an o2 sensor resolving the P0138 and an intake hose that had a tear in it after the MAF, something I overlooked when reassembling everything (wish I would have caught that). Upon return the car had no MIL but it reappeared about 20 miles in. Now it shows code P0430 and P0420. I think the tech just cleared the P0430.

What I don't understand is why I now have a P0420. Did the tech torque down the o2 too much, damaging it? The FSM indicates that will cause problems and MIL.

So, I am thinking that possibly both precats are clogged/faulty/whatever. It feels like the car flat out can't breathe. What to do? I am mechanically inclined, and still have faith in this car. Everything looked real clean under the rocker covers. I have done some research, and changing out these precats looks like a real bear. This is my daily driver. I have done some research about Y pipes etc for this thing, but apparently the precats have to stay. My question to you folks with experience is, is it easier for me to just remove the exhaust manifolds and cats in situ, assemble and replace the entire assembly not fooling with the precat-to-manifold bolts/nuts, or just try to get them out and leave the manifold alone? the one on the firewall (left) side looks like a nightmare. I can either do that, or try to find headers (do they make them?) and use this o2 sim thing? Dealer wants upwards of $1300 to replace perhaps one precat. I am not going there. Any advice, questions appreciated.

freezer

The first thing we need to know is do you have to pass emissions? If not, gut the pre-cats and carry on. Live with the MIL for free or get some O2 sims and that's all.

There's no decent new headers to be bought, you might find some used but they're not cheap.

maximatech12

For it to be clogged you would have had to have drove on it for quite a while after seeing the code.
I had the CEL blinking before I changed the Cat. I bought bad remanufactured injectors.
Even after two years of the P0430 then the blinking CEL the Cat still looked ok but just failed the inspection
Youd have to have pretty sh**** car to have them clog up.

halakar

Hey guys, thanks for the response.

I know I drove the car for a long time (2.5yrs) with the O2 code, not understanding the severity of it. I only have a single O2 on my NX2000 with no pre-cat nonsense. I don't have to pass emissions in VA. There are used header/precats on eBay which is why I was asking if it's easier to just remove the manifold bolts and replace the entire unit in situ. If I choose to gut the precats, what are the risks? There was a guy on youtube using a drill with a paddle bit to ream all the crap out of there. Will gas mileage still suffer with the MIL on? Where to procure an O2 Sim if I try to go that route? I might try to just replace the left (front) precat and see what that does. I dunno. Ugh.

freezer

I gutted my cats when I swapped the motor so I cannot say which way is easier when it's in the car, but I'm sure if you search, the question has been asked and answered.

No, your fuel economy should not suffer with working primary O2 sensors.

If you need sims, these are the best option Intelligent O2 simulators

halakar

Thanks freezer. If I choose to gut the cats, it seems as easy as drop the factory y-pipe and hollow them out using a drill or some other method. As far as primary O2 sensors, what do you mean by that? The ones that are downstream from the ones near the precats? I am still weighing my options - a replacement precat is $214 on rockauto doesn't look like tooo horrible of a job - that is of course bank 1, the one closest to the radiator IIRC.

freezer

Primary is before the cat, 3 wire sensors. Secondary are after cat, 4 wire sensors. The front cat (bank 2), is really easy to gut but it has to come off the manifold. The rear (firewall, bank 1) is a nightmare and I doubt a decent job could be done while in the vehicle.

maximatech12

Every time you have a hesitation its not always a clogged cat.
If you gut the cats thats OK but what id consider is mounting both downstream sensors behind the floor cat.
I didnt say to do that, but consider. that way you run 1 cat and you'll know when it goes bad.

freezer

This is very true. Have you verified your ignition timing? Checked the knock sensor wiring? A bad knock sensor or wiring can also give lousy performance

halakar

Changing out the pre-cat on the front today. Wish me luck!

halakar

Everything has gone from bad to worse. The precat was clogged, could tell by looking at it. Snapped the heads off of two of the lower bolts holding it to the manifold. ****ed it up further trying to drill them out. The manifold will have to come off and be replaced. Does anyone know the tightening/loosening sequence for these bolts?

Child_uv_KoRn

iTrader: (7)

It's called headers if they're that seized and replacing them is a waste of money.

maximatech12

Start pulling sensors and inspecting them!
Start with CSPS, CMPS. I just had one loaded with oil!

TSelanne

iTrader: (2)

Tightening sequence is in the FSM. However.......

IMHO, at this point you're better off getting rid of the pre-cats all together. Not having precats is going to be much better for your car anyway, especially if you plan to keep it around for a while.

And since the 5.5gen front manifold is now messed up, I'd suggest getting 3.0 manifolds. They flow better then 5.5gen manifolds and easy to find. You can get a decent header & ypipe setup from ebay that won't be terribly expensive. And it will bolt up to your stock cat & the rest of your exhaust.

Then you can remove the rear manifold with the pre-cat still attached, it's a lot easier that way, and you won't have to gut them.

If you go this route, you'll get the 430 and 420 codes, so grab a set of O2 extenders. Or if you have any electronic prowess, go on ebay and look for an electronic O2 sim (hint: will have to look for international sellers). Either of these methods should get rid of the codes, the latter being the more certain method.

This is what I would do if I were in your shoes. Good luck. Make that maxima great again!

2k2albatross

Halakar,
The one thing that stands out to me is the "bucking and hesitating." I had the bucking and hesitating but when the car did not buck it actually drove perfectly. My car threw the p0340. This reminds me of my costliest year of ownership. I have receipts that I kept because I was ready to get rid of the car when the dealership could not fix the issue after two tries. On the third try and emails to Nissan of north America they fixed the problem. Here is what it cost and what was done by the stealership:
1/27/2012 – Cam Sensor Replaced
2/22/2012 – MAF Sensor – 846.82
3/10/2012 – New Computer installed by Gregoris Nissan - $711

The old MAF Sensor was returned to me after it did not fix the issue and I received a credit. The new computer fixed the problem according to Nissan. I was very upset when this was all done but at least I did not have to get a new car.

Good luck resolving this problem.

maximatech12

The EC section in FSM even says the ECM is rarely the problem.

The car maybe designed with restricted exhaust in the muffler assembly then during acceleration a valve opens allowing more flow.

This is designed with high quality metal but it could collapse inside after so many years?

If you check the tailpipe and don't feel much pressure the car maybe designed this way?

rodent_infested_03

P0420 and P0430 are likely the result of heavy oil consumption. Or additives like "seafoaming", etc. they foul the catalyst in your converters. If bad enough, you get poor efficiency codes. The two you're getting. If you can geat the REAR O2 sensors off, try the $4 HELP! 42009 spark plug nonfouler trick. Not fixing dead catalyst, rather, pinching the nose of the rear O2 sensors. Then, what the sensors report to the ECU is back to an accepted range. Poof, lights go out. For good. But.. You gotta fix why the catalyst is becoming deficient long term.

maximatech12

He's already mentioned his catalyst was plugged up, sounds like he's got some oil burning.

To have a clogged cat you could say someone used silicone to seal the EM or UIM then the silicone got sucked into the catalyst.

Or a massive melt down, BHG, or shorted out F.I. ?
I wonder if hollowing out the Catalytic converter worked out for the O.P.?

rodent_infested_03

If you can't afford to buy new..

If catalyst is not broken and you can get it off, I see no reason why not to try cleaning it. Supposedly you can to some extent. A mild degreaser and water soak in a trash barrel overnight. then a rinse. Let dry upright for a day or 2, put back on. Now it should have enough flow to clean itself up even more.

maxinout93

Ok I have a question about gutting the pre cats in which I've gutted the front one. Ok I didn't use an o2 extender as of yet. So I've noticed an exhaust leak, as well as the 430 code and a system too rich. So is the fact that the pre cat is not there and there is more oxygen in the system. Is the ecu sending more fuel to be burned under these circumstances??? Tryna figure out why at idle or park my car acts as if it was shut off.

rodent_infested_03

The front O2 sensor is dual role. Measuring the O2 pre-catalyst for fuel trim and catalyst efficiency. The post-cat rear O2 sensor's role is to measure 02 post-cat. The ECU compares the front and rear O2 sensors to determine catalyst efficiency. If the range is not within spec, there is not much diff in O2 range it will throw a P0420 or a P0430 depending on which side of the engine it's on. So if you hollow out the catalyst you must use a spark plug non fouler all you will never get rid of the catalyst efficiency codes. The engine is running rough because of other problems related to oil consumption likely. It's quite possible that if the catalytic converters are clogged you are not able to exhaust so there is not enough good oxygen in the cylinders. That and cylinder spark plugs Etc fouled with oil. I would take things one step at a time fix one thing and then move on to another

maximatech12

Listen to rodent infested
It's got nothing to do with the Catalytic converter.
Both my cats are good and I can disconnect all the 02sensors and the car idles fine.
I'll post a you tube to show you.
That just sends value to the ECM to control the width of the fuel pulse.
Have you tried replacing the fuel pump?
Just make sure you got good fuel pressure, good spark, and good air intake.
After you get that in order it's just fine tuning making adjustments.

maxinout93

yeah I see what u mean I can kinda feel the difference in fuel trim right before the light comes on. But turns out it was either the copper spark plugs I replaced or the maf. Idle is fine now. Now to fix the cat exhaust leak next.

halakar

Hey guys, I wanted to provide an update and thank you all for your input. Since replacing the front precat as well as the upstream and downstream O2 sensors, the car still has no power. Feels like it can't breathe. The only code in the ECU now is P0420, indicating Bank 1 precat. The P0430 code is gone.

My question to you folks is how hard is this part to replace...and what brand precat would you recommend. Nissan OE is out of the question due to cost, there are a variety of brands on RockAuto. I just want the car to be back to normal I also heard that a faulty O2 sensor can cause this issue, but as I have said it feels like the car can't breathe...has NO power. Nissan replaced the downstream O2 sensor on Bank 1 because the car was throwing a P0138 (I think) so 3/4 of my O2 sensors are new. Should I try replacing the last remaining O2 sensor before attacking the precat near the firewall? Also, about the Y pipe...is there any catalyst material in there that could be causing such an issue.

Wild goose chase...sigh.

rodent_infested_03

Not a wild goose chase. You have the codes. Just gotta slow down a bit, work through it. Take it a step at a time. Don't overthink it. Lets start here.

Not sure what you mean by "precat". Both sides of your v6 have an exhaust manifold, then a catalytic converter, then a exhaust pipe. P0420, P0430 are "post cat" error codes. Left and right catalyst efficiency bad. Maybe plugged because of stated power loss. Why both sides? You burning huge amounts of oil? Need to know. Also, stop the Seafoam. Its also mostly oil. You're making things worse, not better using that stuff. Further plugging what appears to be both cats.

Plugged catalyst will cause the engine to stall, lose power at high RPMs. Because the exhausted gasses cannot exit the cylinders. No fresh O2 can come in, it cuts out. Its a exhaling, breathing out problem.

Here's where I need clarification. Are you burning large amounts of oil? What did the mechanic replace to resolve the P0430? How long has the P0430 been fixed? Knowing this answer points us in the direction of fouled catalyst vs vacuum, bad O2 sensors, etc.

maximatech12

I definitely do not recommend Magnaflow pre-Cats! It's a fitment issue. You will need welding equipment.
walker seems like a good fit! I think you'll like a Walker!

Maybe you got crud in the MAF when you tried cleaning it. What your going to have to do is spray the stuff into the tunnels at the base of the sensor.
If you look closely there's metal wires in one tunnel and a metal plate in the other.

You could take some MAF cleaner and simply blast the tunnels real well.

It may just be that the MAF has some crud on it.

halakar

Hey Rodent, thanks for chiming in. When I say precat I am referring to what nissan calls the "three way catalyst" hanging off of each exhaust manifold. P0430 was solved by myself replacing the precat at Bank 2 (front of car, right of engine near radiator).

The car does consume oil as all the early VQ35DE did to my knowledge. I have to put a qt in every 1500 miles or so. There's never any visible smoke from the tailpipe or anything. The car had a misfire prior and I think it F'd up both of the cats. Right now I am of the opinion to try and replace the final remaining O2 to see what happens...but I am not thinking that will fix unless the ECU is putting the vehicle in some sort of limp mode because of bad readings from the last remaining O2.

halakar

Maximatech, I also have carefully cleaned the MAF, throttle body, intake plenum when changing spark plugs, etc.

maximatech12

If you do have a plugged up cat as you posted then your car may not even start.
2K2Albatross and myself also had a Cam sensor issue.
It will cause hesitation and hard start.
As I posted check that.
The P0430 is just an emissions code I doubt it's the root of your issue.
A bad CMPS and a bad H02S and a dirty MAF could lead up to the bucking.

halakar

The car is no longer bucking as an intake hose leak was found after the MAF and fixed. The car just feels like it can't breathe. Floor it, it goes nowhere. Going up steep inclines...forget it unless you have a running start or want to try it at 5k+ RPM. The first thing I want to try and do is replace the last remaining O2 sensor before anything else.

rodent_infested_03

To clarify your breathing statement.. When people write about making their car "breathe better", they are almost always referring to "breathing in". Most assume the restriction is in the factory air box somewhere. They install an aftermarket CAI. Find no difference but noise. IMO thats the wrong direction. I think your problem may very well be breathing, but not inhaling. Exhaling, "breathing out" is the usually the problem, especially with heavy oil burners. Over time the catalyst becomes clogged, leading to a restriction and poor exhaust scavenging. If you can't push enough burnt exhaust gasses out on a piston stroke, there is no room for fresh oxygen. No oxygen, no spark. Depending on RPM, that may cause a stall until you slow RPM enough to keep up with the amount of O2 that can pass through the restriction. A CAI wont, can't change a scavenging restriction. In some cases may make it worse. This video explains some. .
The video provides some insight into an exhaust restriction symptom. Does the back of your Throttle body plate get soaked with oil fast? Thats a clue there is a backup of exhaust gasses bad enough they are backing all the way up into the intake.

Is blocked catalyst your problem? I can't say for sure. But if you're losing power, stalling out on the highway, this may be why..

maxiiiboy

I went through the same problem two years ago, at ~135k miles. Got P0420, and then P0430. To make a long story short, I replaced both pre-cats and the car runs like new. The difference is incredible; at first, I could not believe that it's the same car.

The point is: At 200k miles, your pre-cats are almost certainly worn out and clogged (the only question being "How much?"). So, I would recommend the following:

• Before replacing the pre-cats, make sure your MAF and your upstream O2 sensors are good. Must be bullet proof! Cleaning the MAF did not work for me .... buy a new MAF, or borrow one that is known to work. If your upstream O2 sensors were never replaced, they are very tired; I would consider replacing them even if there is no code.
• If, after the above corrective work, your car is still sluggish, you have two choices: a) You get rid of your pre-cats, or b) You replace them. Note that option (a) is not viable/practical in CA or NY.

There are quite a few threads here describing how to "get rid" of your pre-cats. Just search for "Y pipe", or "gutting pre-cats". In either case, you will need an O2 simulator/extender/other, to eliminate the annoying CEL light which will come on after you drop the cats. If your car is in good shape otherwise, I would go for option (b) instead, and just replace your pre-cats. Rockauto sells some from Walker at very decent prices, and they seem to be quite popular.

Good luck!