Catalytic Converter...

[mijohnst]

Just when I think I'm at the end, something else happens. I started getting the P0430 error about a week ago. Engine seems to be running like a champ after I fix the oil pressure sensor. The engine doesn't sound funny or have any loss of power. I've changed out the downstream O2 sensor on bank 2 back in December. From what I'm reading, I should change out the upstream sensor before switching out the catalytic converter. I guess I can do that, but I feel like it's going to be a waste of time.

Any high recommendations from one off RockAuto or Summit? I've seen some pretty cheap ones on Amazon, but I'd rather just get it done the right way. Looking for recommendations on what I should buy. Also, should I go ahead and change out the muffler while I'm at?

 

[OR VietVet]

If you are going to change out sensors then do Bank 1 downstream sensor. Get a back pressure test done on the cats. Typically the upstream sensor is not gonna set this code. The code has to do with the cats performance and that is read by the downstream sensors. Stand by though, you know another shoe will drop after this repair.

https://www.rockauto.com/en/moreinfo.php?pk=388841&cc=1380372&jsn=2247

The muffler bolts to the back of the cat y-pipe assembly. No need for that muffler if not needed. I would get in there asap and start spraying the bolts at the front and back with your favorite penetrant. This is best I ever used.

https://www.amazon.com/Kano-Aerokroil-Penetrating-aerosol-AEROKROIL/dp/B000F09CEA

 

[mijohnst]

Ron, I love the advice yet again! I just finished putting 2 orders in and I'll start hitting those screws as you recommend by the weekend. I won't get the replacement converters until the next week so I've got time. Thanks again!

 

[THX1138]

I have a 2003 Tahoe LT with 177K.
Received the same o2 sensor codes. Replaced the downstream on bank 2 and it still thru a code. Replaced the upstream on Bank 2 and still thru a code. Took it to another mechanic and they read a bad CAT. Replaced the CATS with a Flowmaster CAT from JEGS.com as well as a new Flowmaster muffler. Codes went away and I kept the old O2 sensors in case I need them again. The bad CATS were causing the O2 sensors to code.

Good Luck

 

[OR VietVet]

Do the penetrant 2 times a day till the work starts or when you know the bolts/nuts are moving freely. When you are working with a through bolt and a nut that is not as critical because that is easily replaced with new. Working on a stud that has a nut on it is more critical when it comes to breaking loose and unthreading. I like to use the penetrant and when I am ready I will actually try tightening the nut a little or if it is a bolt threading in to a captured nut I tighten it a bit too. I like to break it loose by tightening it first. Then I move slowly as I unthread till I can see it will move freely and just take it apart. I have ran across some that fought coming apart the whole way. I have taken up to 15 minutes doing that before. Then when apart and if I am reusing the bolt or nut I clean and lube all threads thoroughly before reassembly. Get the other O2 sensor for downstream bank 1 and replace with the cat system if you are doing that.

If you can afford it and the front sensors are old, do them too. But from the code the only ones to worry about are the downstream sensors for now if you need to wait. If you plan to reuse the upstream sensors use the penetrant on them where they thread in as well.

 

[mijohnst]

I have a 2003 Tahoe LT with 177K.
Received the same o2 sensor codes. Replaced the downstream on bank 2 and it still thru a code. Replaced the upstream on Bank 2 and still thru a code. Took it to another mechanic and they read a bad CAT. Replaced the CATS with a Flowmaster CAT from JEGS.com as well as a new Flowmaster muffler. Codes went away and I kept the old O2 sensors in case I need them again. The bad CATS were causing the O2 sensors to code.

Good Luck

Was installing that Flowmaster muffler a big deal? I'm looking for a youtube but haven't found any installs howtos yet. That either means I need to take it somewhere for welding or it's so easy that nobody would need to make a how-to for it.

 

[mijohnst]

Do the penetrant 2 times a day till the work starts or when you know the bolts/nuts are moving freely. When you are working with a through bolt and a nut that is not as critical because that is easily replaced with new. Working on a stud that has a nut on it is more critical when it comes to breaking loose and unthreading. I like to use the penetrant and when I am ready I will actually try tightening the nut a little or if it is a bolt threading in to a captured nut I tighten it a bit too. I like to break it loose by tightening it first. Then I move slowly as I unthread till I can see it will move freely and just take it apart. I have ran across some that fought coming apart the whole way. I have taken up to 15 minutes doing that before. Then when apart and if I am reusing the bolt or nut I clean and lube all threads thoroughly before reassembly. Get the other O2 sensor for downstream bank 1 and replace with the cat system if you are doing that.

If you can afford it and the front sensors are old, do them too. But from the code the only ones to worry about are the downstream sensors for now if you need to wait. If you plan to reuse the upstream sensors use the penetrant on them where they thread in as well.

Great advice, thank you! I'm going to get it on stands this weekend and hit those nuts and bolts before and after work until those converters arrive. I also ordered all new bolts, nuts, and studs for the job. And because I don't want to do this again for a long time, I bought 3 new OEM O2 sensors to replace the other 3 that I hadn't replaced yet. I'm actually kind of looking forward to it.

 

[drakon543]

doing a muffler swap can be done cheap and easy and well or cheapish slightly harder and really well. anything outside of that and you wasted your time. measure the distance you need to take up between the tailpipe and the pipe before the muffler. pick a muffler you like the sound of and get the overall measurements of length. buy an extension pipe of the appropriate length so the muffler plus whatever you need of the extension pipe will fit. you will also want 3 band style exhaust clamps. also make sure all of those items are purchased with the correct diameter to match your current pipe. and your done with cheap diy properly. slightly better and slightly harder diy would be to replace the mid pipe and tailpipe at the same time. band clamps still fit the bill unless you know someone with 309ss welding then possibly welding it all together so it never moves on you and the 309 ss will last a while at the joints and keep the joints sealed better.

 

[Wylie_Tahoe]

If you have a post converter o2 efficiency code and no pre-converter o2 codes, odds are, its the converter or the sensor.

 

[ks03]

What’s the logic behind changing the bank 1 downstream o2 sensor for a p0430?
Even if you mean bank 2 downstream, 420 and 430 codes set for too much activity (switching like the upstream sensors).

 

[OR VietVet]

Without detailed diagnostics the cats and pipe replacement is a best guess. The bank 2 downstream sensor has been changed already in December, for some reason, and since the likelihood is that the bank 2 downstream sensor is working ok then the source of the problem is again the cat. The cats come as a one piece unit with the y-pipe so it only makes sense to change the bank 1 downstream sensor during this process, to have 2 downstream sensors of relatively the same age. One of the things I should have asked is what brand of sensor was replaced in December?
The P0430 code is all about cat efficiency on bank 2 and that is related to the downstream sensors or the cats themselves. If he is doing all this work I recommended the downstream sensor on the bank 1 side. I also said, again if he can afford it, to do the front sensors as well with all sensors being good quality parts. Such as these:

https://www.rockauto.com/en/moreinfo.php?pk=438154&cc=1412244&jsn=2239


In this case the upstream and downstream sensors are the same.

 

[rockola1971]

Depending on how plugged the cat is you can hit its inlet with a thermal gun and then hit the outlet too and see what the temp difference is. If there is a substantial temp difference then the cat is plugged. I wouldnt expect to see much more than 10-15deg temp difference. Thermal (Infrared thermometer) can be had cheap on Ebay, Harbor Freight, etc.

A plugged cat will be hot on inlet and substantially cooler at its outlet.

 

[Jon Abbondanza]

Just when I think I'm at the end, something else happens. I started getting the P0430 error about a week ago. Engine seems to be running like a champ after I fix the oil pressure sensor. The engine doesn't sound funny or have any loss of power. I've changed out the downstream O2 sensor on bank 2 back in December. From what I'm reading, I should change out the upstream sensor before switching out the catalytic converter. I guess I can do that, but I feel like it's going to be a waste of time.

Any high recommendations from one off RockAuto or Summit? I've seen some pretty cheap ones on Amazon, but I'd rather just get it done the right way. Looking for recommendations on what I should buy. Also, should I go ahead and change out the muffler while I'm at?

Yes such is life with trucks at or approaching the 20 year mark. Better than a car payment, I say!

This is what I bought when my cats failed (not sure what 'do it right' means): https://www.amazon.com/gp/product/B01NARS9TR/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

easy install, decent price, did the job

 

[mijohnst]

I'm in the process of getting the old one off now. I've spent the last 3 days just hitting those nuts on the exhaust manifold with the recommended penetrating oil that Ron suggested. Today I'm working on getting them off. Holy crap they won't budge! They don't look all that rusted either. I really thought that they'd come right out because in several of the YouTubes I've seen the bolts are in way worse shape than mine.

It also doesn't feel right because a 15mm feels just a little too big because I do have some play. A 14mm is too small and a 5/8 is too big so it must be right. It just feels like it's going to round over that nut if I push any harder. So an impact wrench is probably a bad idea, right? lol

 

[George B]

An impact is a bad idea. Heat is my go to with these jobs. I have an oxy/acetylene torch and using a small brazing tip have almost 99% success. Before I had that torch I used this little guy. Just had to have plenty of oxygen tanks.
https://www.homedepot.com/p/Bernzomatic-WK5500-Brazing-Torch-Kit-361487/300055608

 

[George B]

An impact is a bad idea. Heat is my go to with these jobs. I have an oxy/acetylene torch and using a small brazing tip have almost 99% success. Before I had that torch I used this little guy. Just had to have plenty of oxygen tanks.
https://www.homedepot.com/p/Bernzomatic-WK5500-Brazing-Torch-Kit-361487/300055608

And, you can use propane instead but MAP gas gets hotter.

 

[mijohnst]

An impact is a bad idea. Heat is my go to with these jobs. I have an oxy/acetylene torch and using a small brazing tip have almost 99% success. Before I had that torch I used this little guy. Just had to have plenty of oxygen tanks.
https://www.homedepot.com/p/Bernzomatic-WK5500-Brazing-Torch-Kit-361487/300055608

George, earlier I had read about heating that nut up with a propane torch so I bought one at Lowes a few hours ago. I got up there and heated one nut up until it was slightly glowing red and tried again and it will not move. I've been trying to be very careful but I can feel the corners of that nut rounding over. I've tried every 15mm socket I have and they're all the same. They all just feel slightly too large because of the play. It was like that before I even started but worse now. I'm thinking I might need to use a nut splitter to get it off now...uggg. Thanks for the reply!

 

[ks03]

get it glowing bright, as hot as your torch can get it, or stop when you see it deform, melt or bubble, and hit it with the impact. run a rethreader on the studs, and get new nuts to go back on
It is originally a 15. if it’s wilted down from rust enough, I’ve used a 9/16 on a rare few.

 

[mijohnst]

Well, nut splitter it is. I just went out to try again. This time I got the nut glowing red... I put the socket on and it spun completely around and bolded it. Damn it...

 

[mijohnst]

get it glowing bright, as hot as your torch can get it, or stop when you see it deform, melt or bubble, and hit it with the impact. run a rethreader on the studs, and get new nuts to go back on
It is originally a 15. if it’s wilted down from rust enough, I’ve used a 9/16 on a rare few.

Thank you M. I got it as red as I could. Those nuts weren't that rusty either so I don't know why a 15mm didn't fight tight on them. Maybe my Craftsmen sockets are larger than normal or something.