lack of power, possible exhaust leak at manifold flange and/or clogged catalytic converter ?

my 2008, 200k ish? has not had a dash for some time so it flies blind mostly. aside from CEL staying lit (as it always does) still running mostly okay with no major faults putting it into limp mode...

a few days back I noticed a lack of power and HV struggling to stay charged like it usually does. I recently replaced HV with new used from reputable member here and am 99% sure it has nothing to do with that.

on the highway it struggles to get up past 75-80 and when I get on the throttle I hear some racket coming from the front passenger side of engine compartment. at first it had almost a metallic rock or knock/clack sounds, but then after a bit more driving and listening it sounds more of a whooshing / bad gasket sound imo. I also have noticed more exhaust smells finding their way into the cabin, which I initially attributed to whoever was on the highway in front of me, but now think it's me based on all the symptoms that have been coming together.

I had Toyota install new catalytic at the dealer under warranty back in 2014 or 2015, but it has been consuming oil ever since. I drive about 80 highway miles per day, 5 days/week between 80-100mph and fill up with gas every other day and top off my oil with a healthy pour at every gas stop, I would estimate maybe 0.15-0.20 quarts? I do full oil changes every 3-6 months and air filters with MAF cleaning every other oil change generally.

I figured a good place to start would be to check and replace spark plugs even though I don't think the ones I installed last had aged out by mileage, but figure with the oil consumption they could potentially be fouled. While not the best, they also were not as bad as I thought they could have been and I mostly just wanted to get a visual on their condition to see if anything major was going on in the cylinders. I replaced them with new since I was in there but kept them just in case.

I pulled codes using TS, and most all my usual ones were there, along with a lean condition. One thing I noticed that I had never seen before when getting to my plugs was the air filter gasket melted and "chewed" up from the air box lid vibrating or chattering on the one unsecured corner with no clips. it generated a bunch of rubbery "dust" debris on the post-filtered side that was going right into my intake :'( ... I cleaned, installed a brand new filter and added a screw to secure that corner and eliminate the play it had but my theory is that my cat is clogged, the excessive back pressure blew out my manifold gasket, and was back-feeding through my intake and "burping" out the loose corner of my air box lid for some time.

has anyone ever experienced this? I have pics and screenshots I will add in a bit as I am currently on my phone and the uploads keep failing

thanks

 

Yes, I know a lot of things should be addressed with my Prius but it is strictly a commuter car at this point and it has been surprisingly reliable despite being two halves of two different Priuses skinned together and sold with a clean title. Anyways, I made it to my computer finally, so let me rewind a bit...

Monday 12/18 I noticed the lack of power in the morning on my 45 minute highway commute into the office. I work 530am to 400pm, so my days are long and sleep minimal. On top of that, by the time I get home it's either blazing hot, raining buckets, or basically dark out and the mosquitos come out to eat you alive, so weekends are my only time to really address these sorts of things. Anyways, on my way home from the office that day is when I noticed the extra noises... Not sure if I just missed them that morning or not, but it was quite concerning.

Tuesday and Wednesday I spent dealing with home septic issues and Prius sat parked while I worked from home.

Wednesday night I tore into it and replaced the spark plugs, cleaned the MAF, and noticed the concerning airbox issue before replacing the air filter with a brand new one and securing the loose corner of the airbox.

Thursday I had to be in the office again so I drove it in easy not running it hard enough to make the extra noises since I didn't have enough time to look into bypassing the catalytic, checking the exhaust manifold, etc. Same went for Friday... just trying to get through the week since I have ZERO extra time or money for anything absolutely unnecessary at the moment.

Never in all my previous air filter changes have I seen such a thing, nor noticed the corner of the airbox being loose like that. Ideally it is under suction while under load which makes sense why the loose corner shouldn't normally be a big deal in my mind. I plan to bypass and test asap.

Since the upload function of PC is still giving me trouble I will add links to some shots:

1.) Techstream list of codes:
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1a.) Gateway:
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1b.) Air Conditioner:
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1c.) Engine & ECT:
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2.) airbox debris / melted? air filter gasket:
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3.) airbox lid:
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4.) sparkplug shots:
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Regarding codes listed:

P0101 - Mass Air Flow Circuit Range/Performance Problem
-- new code, probably due to air box leaking

P0171 - System Too Lean (Bank 1)
-- new code, probably due to air box leaking

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
-- not sure if new or existing, but doesn't surprise me considering the amount of oil the catalytic has burned since being replaced

P1121 - Throttle / Pedal Position Sensor / Coolant Flow Control Valve Position Sensor Circuit Stuck
-- new code, have replaced coolant control valve in the past to solve, I am guessing probably needs to be replaced again

P1151 - Coolant Heat Storage Tank
-- existing, not new, not worried



B1421 - Solar Sensor Circuit (Passenger Side)
-- full time, existing, not new, not worried

B1433 - Air Outlet Damper Position Sensor Circuit
-- not new, not worried, doesn't bother me

B1442 - Air Inlet Damper Control Servomotor
-- not new, not worried, doesn't bother me

B1443 - Air Outlet Damper Control Servomotor Circuit
-- not new, not worried, doesn't bother me



B1271 - Combination Meter ECU Communication Stop
-- full time, existing, not new, not worried

 

Strike 1 -- again, doesn't bother me, I am used to it and do not care one bit about not having a dash
Strike 2 -- zero battery codes or issues thrown thus far, mechanical noises lead me to believe otherwise
Strike 3 -- surprisingly, no smoke from exhaust noticeable during startup / normal operation the entire time I have owned it and still currently. also no significant amount of black soot, stains, buildup etc around tailpipe tip / rear bumper more than any other car running normally would have. starts and idles regularly, etc. been running it this way since 2014 or so since we bought it used and it has never missed a beat. current cat seems ok since the emissions seem normal whenever I happen to be in a position to observe/smell them.

MAF is still OEM original, cleaned regularly and working fine imo. My concern is the newest noise it now makes under certain heavier throttle loads. Seems linked to air-flow through engine/exhaust system since the noises do not occur while engine is idling / under light-moderate loads, etc.

I thought the "chewed up" air filter gasket was very strange having never encountered it in the nearly 10 years of owning this car.

Sorry not sorry if I drive it like I stole it, I really don't care what everyone thinks of that aspect of it. I run all my equipment to its fullest abilities and am well aware of the additional risks and burdens / maintenance that may come along with such practices. I don't buy things to baby them I buy things to use them how I want.

 

got the cat off, she's clogged:

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yeah I think I might try soaking / pressure washing / chemically dissolving some of the buildup to see where that lands me before jumping straight to a an aftermarket cat. I do have a welder and the tools to straight-pipe it too if need be.

 

to avoid further troubles in the longer term, do you have any quick links handy for faking out the downstream o2 sensor ? I have wires, soldering skills, and electronic components at my disposal and have used resistor mods in the past on my 95 Nissan Maxima, but for now I just want functional bypass details that won't compromise other parts of the engine from running unrestricted for a bit.

 

I am trying not to cut into or destroy my perfectly good (afaik) downstream o2 sensor / wire harness... Was considering unplugging and running a full bypass in the cabin at the plug, but am concerned about the 13.3 ohm heater circuit bypass overheating as I only have 5 1Ohm 100W resistors handy atm and I dont see a 1/4 watt resistor lasting any amount of time. I also dont want to run with my functional o2 sensor zip-tied and powered up on the undercarrigage of my prius while running cat-less in the event of wet weather which we have been getting this week. in the event I do go that route and leave it plugged while zip-tied below, trying to determine if I can shoehorn a resistor/capacitor into the plug or not based on the mods I have read up on.

 

commuted to work this morning with no catalytic or muffler and my attempt at an O2 sensor bypass. I left the 12V disconnected last night with a charger on it to make sure it was topped up, so engine computer and codes also got reset. I've got 80 miles today and tomorrow to run it and see what it throws, but so far a major improvement in throttle feel and HV battery charging problems went away.

 

after cleaning cat:
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reinstalled everything and all is well. no more funny noises. CEL was on when i drove home from work today. got another 80 miles to run in it tomorrow to see how it really feels