2004 GX470 exhaust manifold - catalytic converter question (1 Viewer)

[swissarmyknife]

A little background on where I am at before I post the questions I have.

I have a 2004 GX470 with just over 280k miles on it and have had her for about 2 years now. All is running well but about 15 months ago I saw the first P0420 (catalytic converter low efficiency code) being thrown and the diagnostic with my MX OBD2 reader pointed to a faulty downstream O2 sensor - so dodged a bullet there. Then about 8 months ago the fault came back, this time O2 sensor tested fine (it responded to throttle input immediately and for a short while leveled out around 400mV before it started to fluctuate again). I then ran catalytic cleaner through the tank and the issue seemed to be gone again. Now the error is back for good and it looks like the cat is finally toast. I got time to figure out a solution as my smog check is not due until Aug.

My real confusion and why I am here asking for help is that my exhaust system seems to have 3 catalytic converters. One for each cylinder bank and one downstream after a cross over pipe from the driver side ties into the combiner and right after that is yet another converter. What is odd is that that converter is not monitored by sensors and I looked up the PN (17410-50360) and on Lexus Kendall where the below diagram is from is shows as a discontinued part.

1. Should I not worry about that catalytic converter, maybe even drill it out if it appears to be clogged. That part is also by far one of the most expensive parts at over 1200 and it seems silly to spend that money for a cat that is not even part of the emissions test. I know at the smog place I bring this truck to no probe is used, meaning they solely rely on the OBD2 readout.
2. should I only buy and replace the cat for which the ECU is throwing a code or should I just bite the bullet and buy both. I can get them both from Bells Lexus in Scottsdale for about 1100 shipped.

I don't believe in patching this up with an O2 sensor extension, plus if the cats are really starting to fall apart I am also loosing engine power from increased back pressure.

Has anyone any idea how hard it is to get to the header bolts on both the driver and passenger side? Meaning is this something I could manage on my own without lift or am I better off to bring it to a local shop, hand them the new cat(s) and be done with it?

 

[Rednexus]

The 3rd cat is not monitored by any of the system, so it's can't throw a code. I would be very surprised if it was damaged. But, you can easily check by dropping out the Y pipe and seeing if the honeycomb is clogged/damaged with an inspection camera. If it is damaged, you might be able to fix it with a universal Magnaflow weld-in cat. But I'm not 100% sure if a universal cat is allowed in CA, or if you have to go OEM.

For the upstream cats, here are a few thoughts:
1. If your upstream O2 sensors are at 280k, they aren't working like new and might be the problem. I recommend replacing by 150k. Denso sensors are inexpensive on RockAuto so I'd try them first. Lazy upstream can throw cat efficiency codes.
2. The manifold job is not DIY friendly unless you are an experienced wrencher. The manifold bolts are very difficult to get to. The header install on my VVTI rig took me over 20 hours and was a nightmare. Yours will be a but easier without the SAIS tubes. If in doubt, I'd let a shop do it.
3. I'm betting both your OEM manifolds are cracked and leaking anyway. If the problem does not go away with new upstream sensors, I'd replace both cats/manifolds.
4. Doug Thorley headers are an awesome upgrade if you are doing this job anyway. But, I'm not sure if the are CARB approved or not.
5. I'd suggest making sure the engine isn't running overly rich/lean and killing cats. You can look at long term fuel trims and plug condition to check that. I'd also suggest putting in refurbished fuel injectors at that mileage, as they probably aren't flow matched any more and may have killed the cat.

 

[swissarmyknife]

The 3rd cat is not monitored by any of the system, so it's can't throw a code. I would be very surprised if it was damaged. But, you can easily check by dropping out the Y pipe and seeing if the honeycomb is clogged/damaged with an inspection camera. If it is damaged, you might be able to fix it with a universal Magnaflow weld-in cat. But I'm not 100% sure if a universal cat is allowed in CA, or if you have to go OEM.

For the upstream cats, here are a few thoughts:
1. If your upstream O2 sensors are at 280k, they aren't working like new and might be the problem. I recommend replacing by 150k. Denso sensors are inexpensive on RockAuto so I'd try them first. Lazy upstream can throw cat efficiency codes.
2. The manifold job is not DIY friendly unless you are an experienced wrencher. The manifold bolts are very difficult to get to. The header install on my VVTI rig took me over 20 hours and was a nightmare. Yours will be a but easier without the SAIS tubes. If in doubt, I'd let a shop do it.
3. I'm betting both your OEM manifolds are cracked and leaking anyway. If the problem does not go away with new upstream sensors, I'd replace both cats/manifolds.
4. Doug Thorley headers are an awesome upgrade if you are doing this job anyway. But, I'm not sure if the are CARB approved or not.
5. I'd suggest making sure the engine isn't running overly rich/lean and killing cats. You can look at long term fuel trims and plug condition to check that. I'd also suggest putting in refurbished fuel injectors at that mileage, as they probably aren't flow matched any more and may have killed the cat.

Thank you. Exactly the info I was looking for.

The upstream O2 sensors are constantly oscillating, that is why I figured they are in good shape as that shows the ECU is reacting to keep the stoichiometry in check. The bank 1 downstream O2 is fluctuating with the upstream just not to the extreme but should be nearly flat if the cat was working. At the end it does not hurt to buy and install a new set of upstream O2's or have them on hand as spares.

Regardless, given the age of the cats and mileage the game plan will be to order both upstream cats from Lexus - I checked the Doug Thorley headers, but they would require weld in cats and here in CA it is unlikely any shop will want to touch that even if the cats were CARB regulated. I'll skip the DIY install and have a shop do it, hopefully my go to place has done them on the GX470 before so that I get a labor estimate that is reasonable.

Regarding item 5: Do you have a recommendation on refurbished injectors (came across CS Performance, but have no idea if they are reputable)? Is there a way I can test/check the operation of my current injectors? You hinted looking at the LTFT, so I will take a look at that.

 

[swissarmyknife]

OK, I guess I need to learn a bit more about injectors. CSP for sure seems to know what they are doing, so now the question is, should I opt for the more tightly spec'd 1% flow match or not worry about it? It's an additional 80 which still is waaaaay cheaper than going with Lexus direct new ones at about 190 a piece and I am certain if I ordered a set of 8 I would not get them matched.

 

[Rednexus]

I had a bad experience with CS Performance. They made it right, but I'm not convinced they aren't selling counterfit injectors labeled as Denso remans.

I have Dirty Deeds 12 holes in my rig. For yours, you might have a local shop that can refurbish them with a day or two of downtime after you remove them. Or, send them somewhere like InjectorRX.

You can remove them and test the spray pattern yourself, but at that point you might as well have them refurbished any way. The O rings don't last forever and they will get some gunk in then after years of use.

I only went with the Dirty Deeds injectors as I live in a rural area (no close shops that refurbish them) and didn't want the rig down for a week while they were being sent out.

 

[Poop Bubbles]

All GX470s have two primary cats attached to the manifolds. The cats themselves rarely fail, typically you get a stress crack and a leak in the manifold in front of the cat. The manifolds fail frequently. Does your engine have a ticking sounds on cold starts? Very common.

Some GX's have the third cat after the "Y" joint. Some have a third and fourth cat before the "y" joint. It depends what year/emissions configuration. Your ECM only monitors the primary cats. The models with 4 cats have a shorter pipe going into the muffler, the exhaust is the same otherwise.

Your head is in the right place, whatever you do don't just try to get the code to go away...O2 sensor extensions are for morons and will lead to engine issues down the road. Clogged cats are very bad, great way to burn your valves up.

Some people say the manifolds crack due to dirt packing up in the engine mounts and not allowing enough flex. I can't confirm how true this is but it's worth considering replacing your mounts also given the cost of cats. When my manifolds broke I went with long tube headers/y-pipe and a yotawerx tune. Runs great, power is awesome, no engine codes. I welded a single cat in the stock exhaust before the muffler.

 

[swissarmyknife]

All GX470s have two primary cats attached to the manifolds. The cats themselves rarely fail, typically you get a stress crack and a leak in the manifold in front of the cat. The manifolds fail frequently. Does your engine have a ticking sounds on cold starts? Very common.

Some GX's have the third cat after the "Y" joint. Some have a third and fourth cat before the "y" joint. It depends what year/emissions configuration. Your ECM only monitors the primary cats. The models with 4 cats have a shorter pipe going into the muffler, the exhaust is the same otherwise.

Your head is in the right place, whatever you do don't just try to get the code to go away...O2 sensor extensions are for morons and will lead to engine issues down the road. Clogged cats are very bad, great way to burn your valves up.

Some people say the manifolds crack due to dirt packing up in the engine mounts and not allowing enough flex. I can't confirm how true this is but it's worth considering replacing your mounts also given the cost of cats. When my manifolds broke I went with long tube headers/y-pipe and a yotawerx tune. Runs great, power is awesome, no engine codes. I welded a single cat in the stock exhaust before the muffler.

I am surprised how many YT videos suggest to add an extension to the downstream O2 sensor to pass smog, yeah, for sure not going that route.

No cold start ticking, not that this means there is no leak, but how would that cause a P0420 code? I can see that the B1S2 voltage output is almost as active as the upstream one which I was told is a sign that the cat isn't absorbing the O2 as part of the chemical procss converting toxic gas into CO2 and water.

I'd love to go the yotawerx route but I very much doubt it is CA legal, but I can reach out to them to check.

I had a bad experience with CS Performance. They made it right, but I'm not convinced they aren't selling counterfit injectors labeled as Denso remans.

I have Dirty Deeds 12 holes in my rig. For yours, you might have a local shop that can refurbish them with a day or two of downtime after you remove them. Or, send them somewhere like InjectorRX.

You can remove them and test the spray pattern yourself, but at that point you might as well have them refurbished any way. The O rings don't last forever and they will get some gunk in then after years of use.

I only went with the Dirty Deeds injectors as I live in a rural area (no close shops that refurbish them) and didn't want the rig down for a week while they were being sent out.

OK, not totally rural, but I am not aware of any local shops that do injector cleaning, so maybe I will go the dirty deeds route as well. Still much cheaper than going dealer direct.

I think I got an overall plan.

BTW, 4 vs 12 hole injectors seems to make little difference per this but at the end I am after a clean set of injectors regardless if they are 4 or 12 holes : 12 Hole Injector Upgrade Tested! - ClubLexus - Lexus Forum Discussion - https://www.clublexus.com/forums/gx-1st-gen-2003-2009/938889-12-hole-injector-upgrade-tested.html

 

[Rednexus]

I also just got them as they were the easiest option. I think most of the "improvements" are relative to old injectors with a ton of miles on them .

 

[Poop Bubbles]

No cold start ticking, not that this means there is no leak, but how would that cause a P0420 code? I can see that the B1S2 voltage output is almost as active as the upstream one which I was told is a sign that the cat isn't absorbing the O2 as part of the chemical procss converting toxic gas into CO2 and water.

Upstream leaks can throw off O2 readings and lead to cat failure. Are your cats original? I'd be surprised they lasted that long without replacement (for leaks, not cat failure). Some folks will replace with cheap versions to fix the leak and end up with s*** cats.

In my experience with 4 different GXs over the years.. the factory manifolds will crack long before the cats fail... and the aftermarket cats will fail long before their manifolds crack.

 

[swissarmyknife]

Upstream leaks can throw off O2 readings and lead to cat failure. Are your cats original? I'd be surprised they lasted that long without replacement (for leaks, not cat failure). Some folks will replace with cheap versions to fix the leak and end up with s*** cats.

In my experience with 4 different GXs over the years.. the factory manifolds will crack long before the cats fail... and the aftermarket cats will fail long before their manifolds crack.

Appears to be genuine, but as for if they are the original, I can't tell as I had the truck only 2 years and the person I got it from only for 3 months. He bought it because he wanted an off-roader but then was disappointed in the power output and bought a 2012 460 right away before he sold the 470. The service records I had showed regular maintenance by the first owner up to about 160k, but no mention of any exhaust leaks that would lead to replacement. Then there is about a 60k service gap to 220k miles before I got it and the guy before only had it maybe for 2-3k.

Anyway, not going to take a chance and get new dealer cats, have them installed along with refurb injectors.

 

[Poop Bubbles]

I wouldn't waste money on injectors, or O2 sensors for that matter. If an O2 sensor is bad you get one of several different codes. Refurb injectors are likely to have more issues than old OEM ones.

If you had injector issues, OBD would tell you. If nothing else it would trigger a lean/rich condition based on O2 readings before it was bad enough to damage converter media.

The smartest thing in the vehicle is the OBD. It's smarter than you or I. I have tried second guessing it over and over and it's always right. It's rare but OEM cats do wear out.

 

[Rednexus]

I wouldn't waste money on injectors, or O2 sensors for that matter. If an O2 sensor is bad you get one of several different codes. Refurb injectors are likely to have more issues than old OEM ones.

If you had injector issues, OBD would tell you. If nothing else it would trigger a lean/rich condition based on O2 readings before it was bad enough to damage converter media.

The smartest thing in the vehicle is the OBD. It's smarter than you or I. I have tried second guessing it over and over and it's always right. It's rare but OEM cats do wear out.

A CEL might not be triggered by a single lean cylinder on one bank that is caused by a partially clogged injector. Instead, that cylinder will remain running lean while the ECU dumps more fuel in the other 3 cylinders, thereby getting the O2 ready to "even out", but leading to a mixture that is rich in 3 of those cylinders. Or, one leaky injector would be balanced out by the other 3 cylinder running to lean. Neither of those conditions are good for an engine. The CEL isn't triggered until the LT+ST fuel trims are 25% out of whack.

It's perhaps a bit more real to me as I had a a partially clogged injector burn an exhaust valve and kill 2 catalytic converters on one of my previous Subarus, before I figured it out. It was a Denso injector, just like the ones on our UZs. That engine had 1 O2 sensor per 4 cylinders. Same ratio as a GX. It never threw a lean or rich code as the ECU was able to mask the issue by making the engine run rich, thereby killing the cat, leading to the PO420 code, and eventually a misfire code triggered by the burnt valve.

If you are running around on injectors with 200-300K or more miles on them, monitored by O2 sensors with 200-300K miles on them as well, you are playing Russian roulette with your engine. Some shops can refurbish and flow match them for around $20-25 injector. They are super easy to DIY replace too. Legit Denso O2 sensors are also cheap on Rock Auto and easy to DIY replace. Why chance it?

 

[swissarmyknife]

I wouldn't waste money on injectors, or O2 sensors for that matter. If an O2 sensor is bad you get one of several different codes. Refurb injectors are likely to have more issues than old OEM ones.

If you had injector issues, OBD would tell you. If nothing else it would trigger a lean/rich condition based on O2 readings before it was bad enough to damage converter media.

The smartest thing in the vehicle is the OBD. It's smarter than you or I. I have tried second guessing it over and over and it's always right. It's rare but OEM cats do wear out.

A CEL might not be triggered by a single lean cylinder on one bank that is caused by a partially clogged injector. Instead, that cylinder will remain running lean while the ECU dumps more fuel in the other 3 cylinders, thereby getting the O2 ready to "even out", but leading to a mixture that is rich in 3 of those cylinders. Or, one leaky injector would be balanced out by the other 3 cylinder running to lean. Neither of those conditions are good for an engine. The CEL isn't triggered until the LT+ST fuel trims are 25% out of whack.

It's perhaps a bit more real to me as I had a a partially clogged injector burn an exhaust valve and kill 2 catalytic converters on one of my previous Subarus, before I figured it out. It was a Denso injector, just like the ones on our UZs. That engine had 1 O2 sensor per 4 cylinders. Same ratio as a GX. It never threw a lean or rich code as the ECU was able to mask the issue by making the engine run rich, thereby killing the cat, leading to the PO420 code, and eventually a misfire code triggered by the burnt valve.

If you are running around on injectors with 200-300K or more miles on them, monitored by O2 sensors with 200-300K miles on them as well, you are playing Russian roulette with your engine. Some shops can refurbish and flow match them for around $20-25 injector. They are super easy to DIY replace too. Legit Denso O2 sensors are also cheap on Rock Auto and easy to DIY replace. Why chance it?

Thank you both for your candor and great advice.

I am going to keep this thing for a long long time.

 

[HomersCanyonero]

I’ll throw my own story on the P0420 and P0430 codes I got for about 15 months back in 2020 or so.

I initially replaced all 4 O2 sensors with Denso ones and cleaned my MAF sensor twice and the problem kinda went away long enough to pass SoCal smog tests.

But the P0420/430 came back within a couple months. I reset the codes the rest of the year.

Eventually, replaced the integrated exhaust manifolds with Lexus oem ones and new exhaust gaskets.

My local mechanic only charged me $200 labor total to install both sides. At that time, I paid McGregor Toyota $969 for both exhaust manifolds with integrated cats including the gaskets shipped to me.

I Haven’t gotten the codes since March 2021.

 

[swissarmyknife]

I’ll throw my own story on the P0420 and P0430 codes I got for about 15 months back in 2020 or so.

I initially replaced all 4 O2 sensors with Denso ones and cleaned my MAF sensor twice and the problem kinda went away long enough to pass SoCal smog tests.

But the P0420/430 came back within a couple months. I reset the codes the rest of the year.

Eventually, replaced the integrated exhaust manifolds with Lexus oem ones and new exhaust gaskets.

My local mechanic only charged me $200 labor total to install both sides. At that time, I paid McGregor Toyota $969 for both exhaust manifolds with integrated cats including the gaskets shipped to me.

I Haven’t gotten the codes since March 2021.

Man I would love your guy do the job for me. So far I got one shop quote of 2900 for both sides, waiting on another shop's quote today. If that one also comes in that high I might actually attempt to replace them on my own.

Just checked McGregor and they are sligthly cheaper by about 100 over the place in scottsdale I found. At this point every dollar will help to bottom line.

The injector side I can manage for sure on my own. Just need to keep the work area very clean and take my time.

 

[swissarmyknife]

Interesting, after putting everything in the shopping cart, shipped with tax Bell is only $10 more (no shipping cost VS MCG charges 115). Since the guy at Bell did all the extra work for me confirming the parts I will gladly pay that extra $10.

Also my 2nd labor quote for the exhaust came in at $750, so for sure going that route. Looks like things are coming together.

In case anyone needs the part list for a 2004 GX470 for both upfront cats here is it (confirm by using the diagram in the first post this is your layout and if anything else, reach out to your preferred dealer to confirm directly against your VIN):

Left side manifold
1710550170 - Lexus Catalytic Converter with Integrated Exhaust | Bell Lexus North Scottsdale, Scottsdale AZ - https://parts.belllexusnorthscottsdale.com/p/62999276/17105-50170.html
Rights side manifold
1710450180 - Lexus Catalytic Converter with Integrated Exhaust | Bell Lexus North Scottsdale, Scottsdale AZ - https://parts.belllexusnorthscottsdale.com/p/63056734/17104-50180.html
Exhaust manifold gaskets order 2
1717350021 - Lexus Exhaust Manifold Gasket (Left). EXHAUST | Bell Lexus North Scottsdale, Scottsdale AZ - https://parts.belllexusnorthscottsdale.com/p/63016264/17173-50021.html
Donut exhaust gasket order 2
9008043036 - Lexus Gasket, exhaust pipe. Intake | Bell Lexus North Scottsdale, Scottsdale AZ - https://parts.belllexusnorthscottsdale.com/p/62973191/90080-43036.html
---------------
Here are links to the studs and nuts just in case.
Studs order 16
9008012008 - Lexus Exhaust Manifold Stud. Intake | Bell Lexus North Scottsdale, Scottsdale AZ - https://parts.belllexusnorthscottsdale.com/p/63613012/90080-12008.html
Nuts order 16
9008017187 - Lexus Nut, exhaust pipe set stud bolt. Manifold | Bell Lexus North Scottsdale, Scottsdale AZ - https://parts.belllexusnorthscottsdale.com/p/62972201/90080-17187.html