09 2 newer upstream cat plugged help

So I have been on here before with this issue and doesn't want to seem to go AWAY!

I put 2 upstream cats on my 09 V6 6spd access Christmas of 22. It was throwing the codes PO420/430.

They went away for awhile but they came back after I put the cats on. some one said did I use the double metal gaskets? I said no and I have only had a chance to put them on the drivers side. A couple times I checked the bolts were loose before I put them on, so I retightened them.

I live in PA for now. My check engine light will not go out even if I reset it with my INNOVA OBDII scanner. They come back.

My traction control is on and I have spun out some with the light on as I know it won't work with the engine light on. I am writing all this very quickly as I am in a hurry.

My mpg's are getting worse and I smell exhaust fumes and does my mechanic. I took the truck over to his garage to put on the one gasket. I haven't had time to put the passenger side on as I am in CDL CLASS A TRUCKER SCHOOL.

When we replaced the drivers side exhaust manifold gasket we tightened everything with powerful impacts. The manifold bolts to.

My mechanic put his scanner on and the temps coming from the manifold(going into the cats) is hotter than temps going out(I think I have it correct)? This is after the drivers side metal gasket replacement.

I have two more weeks of school, but what is the problem. Any and all help please.
Brian

 

When you replaced the 2 upstream cats in December 2022, were they OEM or aftermarket?

During this whole process have you taken off the manifolds/cats to inspect if they are blocked?

Do you have another mechanic you can take it to? Parts of your story make me suspicious that your current mechanic knows what they are doing...

 

Sounds like.. 2 new cats on the same side, still acting blocked?
Check downstream then. in my minimal experience, if an upstream deteriorates, all the debris fall into the downstream and clog it.
If it's post-sensor you can punch it clear with a piece of rebar, ect. until you can afford a replacement. I recommend walker exhaust.

I checked mine by unbolting and running hose water through it not sure thats cool, but I knew it was clogged cuz when I removed it and flipped it, a bunch of particulate fell out of the front side. like 1/4-1/2 cup.

 

My cats were aftermarket

The old cats someone said were clean, I may have the old ones still, but they are buried in a tiny shed in some tote that looks like so many of the others........maddening!

NOT two new cats on the same side....both new, both upstream.

 

I've got a video from my mazda tribute job.
https://youtu.be/Z983E0dRlbo?si=_jzlgFOo_9hI0o9Y

From what you've said so far, I'd check the downstream cat - if it's obstructed it can cause back pressure and maybe your issue. Thing is, I wouldn't know what else to say if it's fine and the rest of your exhaust line is fine/new.

I wouldnt worry about aftermarket parts. For the above mazda the owner wanted the cheapest cat/manifold I could get. So he got ultra power. It had an external flange where the shell of the catalyst was welded together, and it stuck out so far it hit the passenger side CV shaft

Some angle grinder work, and
one trip to the welder.. some humbling on our parts. The cheap ultra power headers/catalysts have been on there for over a year with no issues. The cheap sh*t *can* often work. It just often requires extra work that ain't appealing/proportionate to the savings. So much to say dont worry about your brand new cats without reason