Sanity check before cat replacement (1 Viewer)

[et555]

Hi all, thanks in advance for the help. I’ve been a loooooong time lurker here and pride myself on being able to dig up relevant info from this board and answer questions, but I haven’t found an answer to my specific question for today and wanted to pose it to the powers that be.

I’ve got a 2005 w/ 249k that has been my loyal companion since 2010. For the first 12 years of ownership it was primarily a highway vehicle. Over the last 5-6 years my driving habits have changed and the majority of my driving now is a mix of shorter highway commutes (6-15 miles) and city traffic.

For the last 18 months or so I’ve had recurring emissions related codes starting with a P0156 and P0430. I accordingly replaced both the downstream O2 sensors at an indy shop. For about 6 weeks that solved the issue, but then the P0430 returned. I dealt with that intermittently for several months before diving into the problem again. I found that the downstream sensors had not been replaced with Denso, as I requested, but with Bosch. Additionally, the MAF, throttle body, and fuel injectors were all cleaned and the gas cap replaced. I have since replaced all 4 O2 sensors with Denso parts. The P0430 returned almost instantly and I now have a P0420 as well. I can clear the codes, but they will return on the next trip in the vehicle without fail now. I have noticed no change in behavior in terms of power or smoothness over this time. The only other things I would note are:
1) I do feel like my MPG has dropped a bit - I hove around 11.5 with my driving whereas I feel like 5 years ago that might have been closer to 13,
2) sometimes, especially on colder or more humid days, the exhaust fumes on start can smell very slightly rice, and
3) I do have a coolant leak now (getting this addressed ASAP and checking levels every day, seem to loose about a 2 cups / week).

My city-based driving routine and mileage lead me to believe that I may have killed the cats, but given that it’s not a cheap replacement, I wanted to sanity check with y’all before doing so.

In summary:

• Currently throwing P0430 & P0420 codes w/ no noticeable decrease in power or smoothness
• O2 sensors have been freshly changed with Denso parts
• MAF, throttle body, & fuel injectors recently cleaned and gas cap replaced
• perhaps suboptimal MPG & slightly rich exhaust at start up
• daily driving includes primarily city stop & go and shorter highway trips

Anything else I should check / verify before replacing the cats?

Thanks!

 

[jsloden]

It looks like you've done most of the things that you're supposed to. I fought a p0420 for quite a while. I still will get the code but it is very rarely. The only other things I might recommend would be to run a can of fuel injection cleaner through the system. Like bg 44k. I also replaced my gas cap. This actually seemed to help the most. You could also get your mechanic to smoke test your vehicle to check for vacuum leaks. There are several threads on the things people have done in order to correct the issue. Mine also had to do with where I was getting gas. Mine absolutely did not like the gas from this one shell station that was up the road from my house. EVERY time I filled up there the light would come on. It took me a little while to catch on but once I did I stopped getting gas from that particular station and that also helped tremendously.

 

[et555]

It looks like you've done most of the things that you're supposed to. I fought a p0420 for quite a while. I still will get the code but it is very rarely. The only other things I might recommend would be to run a can of fuel injection cleaner through the system. Like bg 44k. I also replaced my gas cap. This actually seemed to help the most. You could also get your mechanic to smoke test your vehicle to check for vacuum leaks. There are several threads on the things people have done in order to correct the issue. Mine also had to do with where I was getting gas. Mine absolutely did not like the gas from this one shell station that was up the road from my house. EVERY time I filled up there the light would come on. It took me a little while to catch on but once I did I stopped getting gas from that particular station and that also helped tremendously.

Thanks for the feedback. I did replace the gas cap too - just remembered that one and added it to the OP.

Worth doing a smoke test, good call on that one.

 

[AFei]

I just replaced one CAT recently but mine was confirmed dead. It was clogged.

Last night, I went through several youtube videos on how to tell if the CAT is good, which you may want to check out. Basically, it just measure the temperature difference between inlet and outlet of CAT. Supposedly, the outlet temperature should be at least 50 degree higher than inlet.

Also there is a hack of lacquer cleaner to clean the CAT to address P0420 code. Several people reported positive but I never tried. Guess it could be a try before deciding to replace the CAT.

Good luck.