P0431:Catalytic convertor replace?Pre-cats 1 unit? trick O2

[redraif]

2001 Montero sport xls, 3.0L Auto trans 4x4.

Code P0431 was here a bit ago and then left long enough for us to pass emissions. Now its back.
Research show:

"Warm up catalyst below threshold cylinders 2-3" (Bank 2)

possible reasons

1. Faulty CAT
2. Exaust leak near rear 02
3. Faulty rear 02

So what are the odds it is the cat versus an o2 misreading? Not sure if the cats have ever been replaced and the rig has 239,000 miles presently. All o2s were replaced no more then 10,000 miles ago, so tthye have a warrenty.

I have it at the shop for the leak around the transmission. He is going to use the scan tool to get some live data on the o2s.

In the inturum I am trying to research the cats. Based on initial searching I had assumed the monitored pre-cats were one solid y-pipe. Since the darn rig is with him I can't look.... grr

But as I'm reading more I'm finding parts sold individually. Am I lucky enough that the 2 precats are actually separate on my rig?

I was trying to figure it out on this diagram, but the resolution is not good enough. I see they cats listed separate on the parts list 12 & 13. and it looks like there could be a flange...



By now I know some of you have had to deal with this as old as the guys are. Any info would be greatly appreciated.

Here are some of the cats I have found... only looking at factory direct replacement fit (bolt on)

These say for the 2001 Sport with 3.0L. No mention of xls not working. (catco)
www.catalyticconvertersonline.com/p-2001-mitsubishi-montero-sport-direct-fit-federal-catalytic-converter-150661

www.catalyticconvertersonline.com/p-2001-mitsubishi-montero-sport-direct-fit-federal-catalytic-converter-150662

but here the very same part numbers and they say will not fit xls

www.ebay.com/itm/01-03-Montero-Sport-3-0L-Drivers-Side-Catco-1065-Catalytic-Converter-NO-XLS-/200778421749

www.ebay.com/itm/2001-2003-Montero-Sport-3-0L-Pass-Side-Catco-1064-Catalytic-Converter-NO-XLS-/190692606236

help clear this fog for me!

another brand that does not say one way or the other (bonsal)
www.partsgeek.com/catalog/2001/mitsubishi/montero_sport/exhaust/catalytic_converter.html

www.rockauto.com/catalog/x,carcode,1440850,parttype,5808,a,www.google.com%2BSearch%2Bfor%2B2001%2BMITSUBISHI%2BMONTERO%2BSPORT%2B3.5L%2BV6%2BExhaust%2BCatalytic%2BConverter

www.rockauto.com/catalog/moreinfo.php?pk=1472578&cc=1440850

www.rockauto.com/catalog/moreinfo.php?pk=1473172&cc=1440850


so what difference does the XLS make??? Sorry I'm still learning this rig!

Magnaflow shows it works on the XLS per ebay
www.ebay.com/itm/Magnaflow-Direct-Fit-Catalytic-Converter-49-State-49511-/201254565390?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AMitsubishi%7CModel%3AMontero+Sport%7CSubmodel%3AXLS&hash=item2edbb4f60e&vxp=mtr

www.ebay.com/itm/Magnaflow-Direct-Fit-Catalytic-Converter-PN-50137-/191479857428?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AMitsubishi%7CModel%3AMontero+Sport%7CSubmodel%3AXLS&hash=item2c9516c114&vxp=mtr

www.ebay.com/itm/MagnaFlow-49512-Direct-Fit-OEM-Grade-Passenger-Side-Catalytic-Converter-/311244878022?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AMitsubishi%7CModel%3AMontero+Sport%7CSubmodel%3AXLS&hash=item4877a3f0c6&vxp=mtr

these guys sell the magnaflows
www.andysautosport.com/hi_flow_catalytic_converter/mitsubishi_montero/2001.html

davico shows it fits the xls as well?

www.ebay.com/itm/Davico-Direct-Fit-Catalytic-Converter-cant-ship-to-California-18149-/381120082915?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AMitsubishi%7CModel%3AMontero+Sport%7CSubmodel%3AXLS&hash=item58bc86f3e3&vxp=mtr

www.ebay.com/itm/Davico-Direct-Fit-Catalytic-Converter-cant-ship-to-California-18237-/381120083179?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AMitsubishi%7CModel%3AMontero+Sport%7CSubmodel%3AXLS&hash=item58bc86f4eb&vxp=mtr

[ES_97Sport]

Jan 13, 2015 14:18:14 GMT -5 redraif said:

...So what are the odds it is the cat versus an o2 misreading? Not sure if the cats have ever been replaced and the rig has 239,000 miles presently. All o2s were replaced no more then 10,000 miles ago, so tthye have a warrenty.

If they're aftermarket O2 sensors? Probably the sensors. 230K? Maybe a CAT, but I'd suspect the O2 sensor(s) first. The factory CAT(s) are very high quality and they really last. My big Sport had the factory CAT for 400K miles - finally cracked it in half on a rock.

...In the inturum I am trying to research the cats. Based on initial searching I had assumed the monitored pre-cats were one solid y-pipe. Since the darn rig is with him I can't look.... grr

But as I'm reading more I'm finding parts sold individually. Am I lucky enough that the 2 precats are actually separate on my rig?

Three peices. The driver side is the CAT and pipe. That bolts to the passenger side that is the CAT, the pipe and Y. So, yes they're designed to be replaced individually - both sides as well as the rear.

... Here are some of the cats I have found... only looking at factory direct replacement fit (bolt on) ....

None. The only thing that makes a difference is whether its a 3.0L or 3.5L and whether its a CAL or FED emissions vehicle.

I presume you have the correct diagram - I didn't check. That diagram doesn't show the flex pipe section between the rear CAT and the Y. Some have the flex pipe integrated into the Y and some have that as a separate piece that bolts between part# 10 and the Y (part# 12). I'm not aware of any Sports that don't have it at all, so .... (well, unless someone took it out somehow)

Wise choice. Stick with bolt-on, not weld in, especially for the forward CATs. Welding on those will totally hose up the flow which will do unpleasant things to your millage, performance, etc.

This is an important rule of thumb for CATs. The more expensive they are, the higher the quality is. This isn't a wives tale, its a fact. The more platinum, the better they work, the higher the cost.

Also, Mitsu's tend to be a little tweeky when it comes to CATs. If there isn't enough platinum in the CAT, it won't work quite the way the ECM/PCM expects and you'll get weird random CELs and codes. Learned this one the hard way.

Make sure if you're in CA that whatever you get is in line with emissions requirements.

Edward

[redraif]

Thank goodness I'm in Georgia, so all is good there. Well the top of the line looks to be the MagnaFlow oem quality direct fir bolt in... $400 & $300ish

I asked my guy to use the scan tool to monitor the live data on the O2 system. Check both fronts and see that they are in line with each other. Cause if a front is off it will throw off the reading comparisons the ecm uses to even determine the cat is bad.

Hoping that will send a red flag and an O2 is hiccuping. Some of them are aftermarket. The fronts I believe. Another reason I want him to verify them.

The rears, at least one, is mitsubishi.

[ES_97Sport]

Jan 14, 2015 10:56:17 GMT -5 redraif said:

Thank goodness I'm in Georgia, so all is good there. Well the top of the line looks to be the MagnaFlow oem quality direct fir bolt in... $400 & $300ish

I asked my guy to use the scan tool to monitor the live data on the O2 system. Check both fronts and see that they are in line with each other. Cause if a front is off it will throw off the reading comparisons the ecm uses to even determine the cat is bad.

Hoping that will send a red flag and an O2 is hiccuping. Some of them are aftermarket. The fronts I believe. Another reason I want him to verify them.

The rears, at least one, is mitsubishi.

Ouch! That's like OEM pricing. Have you checked OEMMitsubishiParts to see what the OEM parts cost?

Yep, no doubt. I'm in CO so I still have emissions to deal with but not as bad as CA. Still, make sure you have a FED Sport and not a CAL one.

The spurious behavior makes me think O2 sensor, but I had a cheap aftermarket CAT that would cause the same behavior. Nerve wracking because neither sensors or CATs are cheap - not something you want to play musical replacement parts with.

It'll throw off more than that, but you're correct.

Edward

[dclambertt]

www.justanswer.com/mitsubishi/5t1p3-mitsubishi-montero-limited-does-code-p0431-means.html

[redraif]

Jan 14, 2015 17:36:06 GMT -5 dclambertt said:

www.justanswer.com/mitsubishi/5t1p3-mitsubishi-montero-limited-does-code-p0431-means.html

I had read exactly this when searching. This is why I suggested that my mechanic check the O2s.... just to be sure. This reference says was rare, but just in case...

[redraif]

ok... reporting back in. So we changed the front and rear o2s on the drivers side. both were spitting out bizarre irratic values on the live data. This stopped the code for about 150 miles. Then the p0431 returned, so now we will replace the cat.

The shop says the brand is AP cost is around $250? Anyone heard of the brand? I was leaning towards the magnaflow OEM quality direct fit bolt on replacement ($290)

Its gonna take a minute to come up with the funds as this rig is draning us dry. Still dealing with the transmission fluid leak. So that being said I will shop around to find what is the best one. Just don't have the $ for the Mitsu one. How quick would you suggest I address the cat? More time means I might be able to save up for the Mitsu one. Plus it would be nice to get a flowmaster at the same time.

How bad is the drivers side unit to replace one's self with hand tools and a jack only (no air tools or lift)? Do I have to drop the entire exhaust... aka work from the back to front removing things till I reach the pre-cats? If so I might wait till I can do the entire exhaust with a flowmaster. Are the flange bolts prone to break? Body bolts were no problem for the lift. No siezed or rusted bolts. But the exhaust is SUPER SUPER muddy.

Speaking of cats... if the rear one is not monitored.... could one not delete it when adding an aftermarket exhaust?

Or even.... if the rear cat is ok... what would happen if I moved the drivers rear O2 behind the rear most cat and deleted the bad precat. Would that trick the ECM?

Better yet...I wonder if the mil eliminator style like the Mustang's would work. That could buy me some time and I could even delete the cats and upgrade the exhaust.

www.newcelica.org/forums/showthread.php?t=216641

Another idea... spark plug non-fouler

www.mazdaworld.net/forums/index.php?showtopic=2548

honda-tech.com/acura-integra-type-r-8/spark-plug-non-fouler-1841240/

www.pirate4x4.com/forum/dodge/688671-mil-eliminator.html

Maybe the mil elim and non-fouler trick.... just to get the monitored pre-cats off. Our inspection station does not even look under.

Creativity when you are out of cash... LOL!

[ES_97Sport]

Jan 21, 2015 12:39:10 GMT -5 redraif said:

... How quick would you suggest I address the cat? More time means I might be able to save up for the Mitsu one.

I don't know what the brand is that they put in mine so I'm not much help there. I beat on them about putting in the best aftermarket they could get, though. It ended up running about $175 for the CAT. This was the big single CAT in my '97 so pricing will be different for the down pipe cats.

I can say this, though. The quality of the Mitsu CATs is higher than the aftermarket ones. I noticed when we pulled what was left of the stock CAT out and I compared it to the aftermarket ones. The stock CAT was heavier. Part of that was the outer shell and heat shield - that was obvious.

I ordered in a set of down pipes from Mitsu and the came in a week ago. These are the pipe from the driver side manifold to the Y pipe from the passenger side manifold. I've been looking at replacing those with aftermarket ones since we did the engine swap 3 years ago. After looking at the aftermarket ones, I decided that wasn't the direction I wanted to take. The aftermarket ones are about 1/2 the weight and are missing all the heat shielding. The tube quality isn't a huge issue but makes me wonder how long before they rust through. Missing the heat shielding is a real PITA in high ambient temp locations like Moab in the summer. I finally had to use exhaust wrap and wrap my down pipes down to the Y to cut down on the heat baking everything under the engine. The other thing I really didn't like was that the bends are radiused not mandrel so they restrict exhaust flow in a critical part of the exhaust system. Overall, the OEM ones were about 1/2 again as much, but the they're obviously a lot higher quality.

SO, its up to you. You can afford what you can afford. My recommendation though is if its at all possible to go with OEM CATs. But, you gottta do what you can afford.

... How bad is the drivers side unit to replace one's self with hand tools and a jack only (no air tools or lift)? Do I have to drop the entire exhaust... aka work from the back to front removing things till I reach the pre-cats? If so I might wait till I can do the entire exhaust with a flowmaster. Are the flange bolts prone to break? Body bolts were no problem for the lift. No siezed or rusted bolts. But the exhaust is SUPER SUPER muddy.

I've had mine off several times. If you have a breaker bar you shouldn't have any problems with the bolts so an impact gun isn't necessary. I've always used normal hand tools. Make sure you saturate all the bolts and nuts with PB or LiquidWrench good and let it soak overnight. That will help immensely especially with the manifold bolts. The very last thing you want to do is snap off a seized manifold bolt.

Oh, and don't forget to get gaskets.

No, you only need to drop the piece(s) you're replacing. If you're doing both down pipes, its the manifold bolts on both sides, the driver side down pipe -> Y pipe, and the Y-pipe -> rear CAT bolts. Not that big a deal really. Since you already have had the O2 sensors replaced, those will come out easy. Get yourself a can of COPPER anti-seize for the O2 sensor threads for when you re-install them. DO NOT EVER EVER EVER get anti-seize on the sensor itself. The chemicals will ruin the O2 sensor. And don't spray them with any kind of cleaner either.

If you're going to do the entire exhaust (from the CAT back) with a Flowmaster - and you might as well do this, rather than replace JUST the muffler - make sure that the biggest you go is 2.25". It won't cost you more or less to go from 2" to 2.25" so there's no savings there. I've priced this a bunch of times over the years and there's little cost savings between replacing the muffler with a different muffler and just replacing the pipe and muffler at the same time. It usually comes down to cost of a few extra feet of pipe and maybe about 1/2-1 hour of labor more. They guys I use charge the same either way because they have to almost tear out the entire CAT-back system just to do a muffler anyway.

The manifold bolts are the problematic ones. Their not bolts, they're studs so if you snap one .... Hence why I said saturate them in PB or something for a day. Warm up the engine to operating temps, let it sit for an hour so its still warm but not hot and spray the crap out of them. If they're really bad, spray them and come back about 6-8 hours latter and spray them again and let it sit for a day. DO NOT drive it, just let it sit and let the PB do its thing. The others are bolts and nuts. If one snaps off, get another grade 3-5 bolt and nut. As long as its the correct size anything from a hardware store will work. If they're REALLY REALLY bad, you may want to replace them just to save you from possible issues down the road if you ever need to touch them again.

... Speaking of cats... if the rear one is not monitored.... could one not delete it when adding an aftermarket exhaust?

If there's no O2 sensor in front of and to the rear of a CAT, its not monitored.

In theory, yes, because the ECM/PCM won't actually know - the only info our Sports get on the CATs comes from O2 sensors. In practice, it depends on whether you have to pass emissions and where you have to pass. Technically its illegal. Federal law prohibits removal of CATs and I don't recommend doing this ever because really, they do good things for the air we breath.

There's no benefit from a performance perspective, if that's what you're thinking. The factory CATs flow more than a N/A 2.4, 3.0 or 3.5L can actually put out. Couple guys long ago fiddled with this and no one every found any difference. This has even been looked at on a dyno, so ....

Keep in mind that if you ever plan to sell your Sport and its missing a (or more) CAT, you're limiting your buyers to others who either don't care or don't have to care. Frankly, if I were looking at a vehicle and saw that, that'd be a major red flag for me. My perspective is this is done by people who don't know or don't care and either one makes me wonder just what else they've fiddled with that I may have to fix. Anyway, just my 2 cents.

... Or even.... if the rear cat is ok... what would happen if I moved the drivers rear O2 behind the rear most cat and deleted the bad precat. Would that trick the ECM? I wonder if the mil eliminator from teh Mustang would work. and again... delete the precat.... hmmmm....

Ok. No, none of that will work. In fact it won't work for some of the same reasons that I can't put '00+ CAT down pipes on my '97-'99 Sports with only one CAT.

The ECM/PCM is programed for AN O2 sensor in front of and behind ONE CAT. You CAN NOT put one in front of a CAT and the other behind a second CAT. So, you can not have O2 sensor -> CAT -> CAT -> O2 sensor.

Secondly, you can not use the rear (main, big) CAT as a replacement for the down pipe CAT(s). For one thing, the CATs are of different efficiency. That won't make any difference to the fore O2 sensor, but it can make a difference to the aft O2 sensor.

More importantly the O2 sensors are there to feed the ECM/PCM data used in managing fuel control - such as HOW MUCH or HOW LITTLE fuel is fed to the cylinders. The left and right O2 sensors actually feed data for the left and right banks of your engine - so 3 injectors each. This is unlike the '97-'99, which only has one set of O2 sensors that feed data for the ENTIRE engine - all 6 injectors. So, if there is a problem with one O2 sensor you can have one side of your engine running lean. Or, its possible if two are screwy, you could have one side lean and one side rich.

Now, the forward O2 sensor reads the exhaust gas coming out of the engine. The rear reads the exhaust gas coming out of the CAT. Contrary to popular belief the notion that the rear O2 sensor doesn't play a part in fuel management is BS. If you read the FSMs carefully, there are references that make it clear that both O2 sensors are used. In addition, the 3G/GT guys have reverse engineered the PROM code on the Mitsu ECM/PCMs and that is clearly how it works. The rear O2 sensor is not a major player, but is most certainly used. Which is probably where this came from - you can remove the rear O2 sensor on say a '98ish and it will still run, and probably most people wouldn't notice the difference. I have and you can tell if you know what to look for and you're sensitive enough to your vehicle.

Anyway, so if the CATs are of different efficiency, like using a down pipe CAT for one side and using the main CAT for the other side, the exhaust gas coming out will be different which will throw off the math inside the ECM/PCM because the ECM/PCMs are programed to expect data coming in to be within a specific range and to look a reasonably specific way. The static data programed into the ECM/PCM is based on the operation of the CAT that the manufacturer uses for that vehicle. Change the CAT, change the output data, screw up the ECM/PCM, screw up your fuel control. Its that simple.

Now to specifically address your question about plumbing in the rear O2 sensor AFTER the main CAT - Uh, no, that's not a good idea. That will be after the Y pipe so what you will be measuring is exhaust from both banks after ONE of the sides has been through a CAT already. So, while this would PROBABLY run 'ok' it will screw with the fuel metering on one bank. How this will work from a CEL standpoint I can't guess. The ECM/PCM will also trigger a code and CEL if the exhaust is too 'clean'. So, there is an upper as well as a lower bound that can not be exceeded.

As for your O2 eliminator - yes, our Sport will run with an eliminator in the rear O2 sensors. Our Sports aren't that much different from Eclipses or GT3000s or such. The downside - you loose diagnostic ability as well as screwing with the fuel system so you'll loose efficiency.

The way you work around the efficiency is to just not care if you're a turbo boy racer, or install some kind of piggy-back, programmable ECU thing and Widebands and spend your life tuning the crap out of a vehicle that ran fine before you messed with it for no reason. If you're doing F/I I can see the point, but not for this. That would just be horking up a system that runs fine as it is.

Eliminate one SET of O2 sensors? No, not a remote chance in hell. You can NOT use an eliminator in a forward O2 sensor in a computer controlled system unless you have something else to replace the 'control'. An eliminator feeds a static signal to the ECM/PCM. The signal is 0V to 1V, if I remember correctly, so 0V is lean and 1V is rich. One is saw was set to return a voltage that equaled stoichiometric for gasoline which is what, 14.7? Others were set a little rich or a little lean but still returned a static signal. That's fine but fuel needs to increase under load and decrease under deceleration/light throttle. In other words, its not static. You have effectively turned your computer controlled vehicle into a carburated goat cart from about the 1890s. Even a carburetor does not supply fuel statically.

So, how do the guys doing this get away with it? Exactly the way I said above. They replace the narrow band O2 sensors which is what Mitsubishi uses in everything up to and exceeding '05 with Wideband O2 sensors and a aftermarket ECM (which, BTW, you can not do) or a piggy-back ECM like the AEM F/IC that I use to take over management of the fuel from the original ECM/PCM and original O2 sensors.

Edward

[redraif]

So we have been saving for the new cat after replacing the o2 on that side did not help.

Light was on a bit before
239652
Light turns off @
240312

How often does this happen? What could have caused it to be on and go back off?

[russiankid]

I have the same issue except for bank 1. I am not sure whether it the O2 sensor or cat failing. I have an exhaust leak at the flex pipe that I haven't fixed yet, but I just keep resetting the code when it pops up, usually pops up once a month.

[redraif]

From my research an exhaust leak will throw the code as well. Fix the leak in the exhaust before you replace anything as you know that is a known issue. Then go from there

[russiankid]

I plan on just welding up the leak, I just haven't got around to it with work.

[ES_97Sport]

Mar 11, 2015 8:04:18 GMT -5 redraif said:

From my research an exhaust leak will throw the code as well. Fix the leak in the exhaust before you replace anything as you know that is a known issue. Then go from there

Correct - depending on where the leak is. Pretty much any leak in the system BEFORE an O2 sensor can trigger a CEL and code.

Some OBD codes will reset themselves. They're not permanent - requiring a OBD computer reset.

Pretty much. I don't think any of us have the test equipment to do this the 'right way'.

Edward

[redraif]

So Edward, should I assume my precat was ok all along? Any idea why it would be on for so long and then go off and stay off? Just dont know if I need to keep worrying that i need to replace the dang thing. I hate to spend the money elsewhere only to end up needing it for the cat....

[ES_97Sport]

Mar 16, 2015 15:52:25 GMT -5 redraif said:

So Edward, should I assume my precat was ok all along? Any idea why it would be on for so long and then go off and stay off? Just dont know if I need to keep worrying that i need to replace the dang thing. I hate to spend the money elsewhere only to end up needing it for the cat....

Short of looking at all the OBD code criteria, no. In my experience the emissions codes are a PITA. If you haven't already, do some surfing on the Mitsu Sport 'readiness tests'. That should give you some idea of how convoluted the emissions stuff is. Telling exactly why something comes on and then goes off might not be an answer you will ever get. From anyone.

Don't know. If its off and stays off for a couple months, then I'd leave it alone. If you REALLY have CAT problems, it won't stay off. My gut thinks that maybe you had something else causing that code - that would explain why it quit and hasn't come back.

They only thing you can 'fix' with a CAT is a leak. There's no amount of magic rubber chicken waving that will make a CAT get better. Once they're shot, they're shot. So, if the code goes away I'm strongly inclined to believe you fixed something else.

I'd be patient. Sometimes CAT errors take a while to show up. Not what you want to hear, I'm sure, but I'd let it run for a month at least of daily driving.

Edward