Replaced CAT&O2 but still sometimes failing emissions sometimes not

Bought an 04 with 190k miles for my daughter. Lots of little issues.

It had a bad cat and was failing cat/02/evap on the Car Scanner + veepeak OBD2.

I replaced the cat and O2 sensor and have driven it 75 miles since. Sometimes in the scan, it shows all 3 still failing, mostly if it's stop and go in town or driving up hills (Oregon hills, not flat country hills). Sometimes the scan shows all 3 passing, usually off highway. But usually it shows cat and 02 passing but evap failing.

Now, when I changed the oil after buying it, I got only 3/4 of one quart of oil in the pan.

Cleared that, added oil and a new filter.

What else can I do to improve the combustion cleanliness? I'm assuming that's the issue but I don't know where to start. Change oil again? Clean manifolds?

 

It's a VEEPEAK2 OBD scanner. Usually plenty good enough.

What about the other questions? Could it be a dirty manifold etc, what could b causing the engine to combust poorly or push extra dirty air out?

Remember the effort the engine is giving is what pushes the scanner to show pass fail, so it seems logical to think it's a combustion issue. But I don't know enough about cars outside of that deduction to indicate what.

 

Sorry I wasn't more clear.

2004 Prius 190k miles bought in Nov for my daughter. I drove it two months earlier, drove beautifully. Couldn't believe this car, West coast US, was $1000. Seller needed to wait until his move to Korea to let it go, and I let him use it till then. He said it needed a cat.

Upon taking custody of it, it kept getting a red triangle warning. Turned out to be low oil. So I changed the oil myself, but when I did, the engine had only 3/4 of one quart of oil come out. And the oil was super thick and chunky. Bad sign.

Yet it doesn't seem to burn oil.

It runs beautifully since the oil change.

Seller said the cat was bad and it smelled like it, so I got a scanner. It showed it failing. I took it to DEQ to confirm and it failed there.

Replaced the CAT and O2 but have not been back to DEQ, as the wait is always over an hour. Since the scanner was correct to DEQ before, I assume it is now.

Why it sometimes is showing passing and sometimes not, I don't know. But they test emissions in Portland area and cat and evap fails are never allowed through.

I don't understand what's going on to make it sometimes pass and sometimes fail unless it's a crusty dirty engine, maybe from that super low oil before, or the exhaust manifold is just dirty and burning off crust? :/
Would a dirty throttle body or intake manifold do that? Timing?

I did yank the entire interior and scrub it all, as it looked like a road worker owned it, heavy road tar on seatbelts and seats carpet etc. but all came out. Also found lots of bullet casings and rough gravel from forest roads, so I think they first owner took it up shooting a lot. Not exactly an ideal car for mountains logging roads lol. So who knows how it was treated poor gal.

I'm in an apartment after my divorce so I'm trying to get ideas before I take it apart due to the situation I face trying to work on it here.

I hope that is more helpful and clear for you.




The interior

 

Oh I forgot to add, gas mileage is 38-41. I've driven it back and forth to Seattle 4 times, 6-7 hours r/t.


Also after the cat swap, sitting parked with engine running, it still smells a small amount like heavy old fashioned exhaust sometimes, like there is some kind of leak. Where would that be at?

 

Yah in the PNW the gas in the winter has a funky mix, and mileage goes down in every car.
Interesting on the regen oil use. The young man who had it was a brand new father of 20 years old, moving to Korea to teach English with his young wife, cause they just couldn't swing the expenses here. I think even a quart of oil was pushing their finances so I understood why he let it run low. I gave him an extra 500 for the car to help them out.

Anyways,

No codes now, just on the exhaust section of the Car Scanner app indicating fail or pass, but DEQ does pick up on that.

No smoke or smell of burning oil. It smelled rather distinctly of 1980s car exhaust when I picked it up.

After replacing the cat - where I used JT brand which was $200 on amazon compared to the $80-90 of the cheaper brands - the smell vastly improved.



However, sometimes when the car is at rest at a light.and regen is running strong, it still smells a bit, like a rare waft, of 1970s-1980s exhaust.

So I was wondering if either the exhaust manifold gasket at engine was bad... or the gasket between the exhaust manifold and new cat wasn't seated well. I'll have to determine that.

I did reuse the same bolts on the car install. I think they are the originals.

This car, it appears it had the cat stolen. There was a replacement unit - but it had been welded directly to the second Futaba section (under the rear seats) which has been cut where the diameter changed from exhaust size to 6-7". Normally there is a slip over pipe there, but it had been cut and welded. Pain to fix.


I did not change the AF mixture sensor behind the engine. I only changed the O2 between the cats. I'll do that as well and see if anything improves. Edit: ordered a Denso but takes a bit to get here. I'll report back once I do.

I also ordered Denso plugs and fuel injectors just in case that's an issue.

 

Think I must've gotten a bad price in the fluctuations Amazon uses. Should have checked with camel camel camel. Napa wanted $583, so I hopped on Amazon to compare, and went with a mid grade. Or so I thought.

Well it's cut and welded now so I guess it's staying. Shoot