Missing CAT Mystery

Where did it dissapear to ?
entire catalytic converter looks gutted clean :


long story but bottom line is, Code came up last week PO420 (insufficient cat function)
removed it and found it missing.
Probable causes ?
(now for the long novel)
I had a severe misfire event in an all day heavy downpour of rain and drove it 300 miles to home with it sputtering, instead of calling a tow truck or trying to find an open auto parts store at 8pm on a Sunday in a torrential daylong downpour
Misfire code came up
I found a jumping plug wire and replaced it then cleared the code
It ran fine for about a month , then I heard the CAT death rattle
( UH OH not again )
last time I heard that was after the head gasket blew, changed out motors but CAT was contaminated and melted
Previous owner had the OEM cat stolen and just had an aftermarket welded in place, it lasted 80,000 just for me but after the motor change it went out soon after
So I welded in a 2001 Toyota OEM front cat that I had around and it lasted 10,000 miles until the misfire event
How could it look gutted clean ?
recently , before the PO 420 code a PO 401 code ( insufficient EGR ) came up, went through the entire EGR system and found nothing, code would not clear.
I kept trying things and changed plugs and cleared codes , then the CAT code came up.

Big question is :
am I running lean ?
or is this all the result of the misfire event

I managed to find an exact replacemnt full OEM used exhaust system out of a light crashed exact same truck and hope I dont burn this one up :



Do these plugs look lean ? came out before the 420 CAT code came up, the look pretty brown to me and not unusually lean for fuel injection


the exhaust system I got had stock toyota 02 sensors but the looked pretty crusty
I put my old aftermarket 02 sensors back in
It seems to run perfect with NO CODES after 100 miles
I looked for glowing pipes and used a lazer thermometer seems to stay pretty steady at around 400F even after running at 70 mph then pulling over and revving to 3000RPm at headers and catalytic converter ( I installed OEM 2001 prerunner pipe headers)

Will the 02 sensors effect fuel trim ?
should I get new Denso sensors?

 

Iam starting to think the PO 401 (insufficient EGR ) was somehow related to the catalytic converter going out ,
perhaps by an unballanced reading between the 02 sensors and the EGR temp sensor ?

 

I shook the muffler and it sounds full of loose junk and the seam looks expanded like it tried to blow out

The old OEM catalytic converter I just got looks good at both ends but the pipe is pretty sooty
I replaced all the nuts bolts and gaskets

 

I will presume that the upstream 02 sensor can be not operating at optimum reference voltage for correct fuel trim without lighting the check engine light ?
so in other words it can be bad without sending a code ?
if it is falsly reading less oxygen content because it is dirty then it sends a signal to the ECU to lean out the fuel injection
if it is low on fuel pressure then it will send the signal to richen but it wont be able to
I suppose a scanner will tell the story ? ( I only have code reader)
I suppose it would be wise to just replace the upstream sensor to be on the safe side ( $50 to 100 for the denso ) ?

 

Well for starters, you are using the wrong plugs. You need to be using dual electrode plugs.

 

He's running the right plugs. Only one I know off the top of my head that used dual was the 3.4
This is the stock plug for a 1998 Tacoma 2.7:

 

Oops. Shouldn't have skimmed

 

Are you the original owner?
Previous owner may have gutted the cat.

 

No not original owner
I got it with 160,000
now has 270,000
Original owner said the OEM cat got stolen
he replaced it with an aftermarket CA cat,
worked great until 250,000 and head blew and hydrolocked
I replaced motor and all engine controls
soon after cat burned out
I got a PO401 code back then
I replaced the burned cat with a used front cat from a 2001 prerunner with 2.7 from the motor I got out of a crash to replace my 1998 motor with blown head gasket

thats what is so weird
the cat I just took out looked gutted clean
The other cat that burnt out after the motor blew was just shrunken and rattling around in there
this one dissapeared
malfunctioned after about 20,000 miles

 

Check engine light came back on after after installing the used OEM system : PO420 again and PO420 pending
I suppose I should get a scanner and try to figure out what is going on
Hopefully the "new" used cat I just put in didnt melt away or dissapear after 100miles
it looked just fine before I put it in but real sooty
I probably should have at least got a new front 02 sensor
or put in the OEM 02 sensors that came with the sooty exhaust I just put in
GAWD I hate going to a shop for tech stuff on an old truck like this, usually they just give you the fiddle sign and say "have to drop it off for a few days so drop your drawers and open your wallet"
I took it for an $80 diagnostic to a Toyota dealer once because it was stalling at stop signs when cold, they charged me the $80 and said they couldnt find anything wrong after leaving it for 3 days....never again !

 

I think you are on to something, It could be I am using the wrong brand of oil too,

but thanks for the bump

 

Got some Data
40 mile drive freeway and city
now I just need to study up on what it means :
this is the stored code event

Live Data :
it appears BOTH front and rear (aftermarket unmarked) 02 sensors are fluctuating steady between approx. 0.9 V and 750v
this was snapped at the low point of the wave at about 2800 RPM

ECT sender seems to be working ( not sure what calc load is ) :

Fuel trim is pretty consistent in the -2 to -11 range throughout
as far as I can tell so far , it must mean that bthe front 02 sensor is reading rich and ECU is trimming -2.5 or whatever
short term STFT
long term fuel trim LTFT :

TPS seems set at 9.5% at idle not sure what that means ?
should it be 0% at idle ?

 

FYI if anyone is interested
Gettin no love here but found the answers through hours of you tube study concerning what causes the P0420 code and explanation of fuel trim interpretation.
also assured interpretation of my fuel trim parameters ( long term and short term) are within factory recommended range using the scanner in all driving condition for an extended period (80 miles) so that I do not burn up another CAT
this helps to confirm my conclusion the the CAT destruction was caused by the misfire event and not incorrect fuel mixture ( too rich or too lean can burn up a catalytic converter)
I obtained the Toyota Factory Service manual for my exact vehicle and found the range numbers fall right in the middle so I think my Fuel trim is correct and no lean or rich condition so I dont see the need to check fuel pressure
found out that "CALC LOAD" is "current air volume as proportion of max intake volume" which is also in range
I can now purchase a new catalytic converter with the option of replacing the 02 sensors (not mandatory) with the peace of mind of knowing that I am not just "throwing my wallet at it" and did a somewhat informed tech diagnosis
evidently the used cat was bad, probably from sitting out in the rain and blowing dust, but now I can just bolt up a new proper California Cat

 

also found
The PO420 code indicates an failed Catalytic converter when the Voltage values between O2S1 and O2S2 fluctuate in similar wave pattern switching rapidly at the same rhythm between 0 and .9 v
a properly function CAT will show the front O2S1 fluctuating between 0 and .9 and the rear should be reading fairly steady well below .5 v
a bad (or lazy) 02 sensor will fluctuate slowly or irregularly not in rhythim

negative fuel trim numbers (-7) indicate that the 02 sensor is reading LESS oxygen and sends a signal to the ECM to give less injector pulse to make it mopre lean
Positive fuel trim numbers (2.2) mean the 02 sensor is detecting too much oxygen and ECM sends more fuel
the short term FT numbers are not necessarliy an indicator of a problem, it depends at what RPM and temp, and so forth
the long term fuel trim numbers are more of a record of the average and are more of an indicator of a fuel delivery problem
howeever besides fuel supply, other factors such as intake/exhaust leaks or MAF sensor signal can also have an effect on LTFT

 

I have a plausible theory ( that could be total bunk ) as to why the code P0401 (insufficient EGR) came up.
goes as follows :
as the Catalytic converter first started to break down, it caused exhaust backpressure to rise. When the EGR temp gauge told the ECM to switch EGR VSV to open, exhaust gas did recirculate into the intake, but the front 02 sensor was unable to detect any change in oxygen content because of the increased backpressure and ECM thought that the EGR was not operating at that time. (?)
......the rear 02 sensor was also restricted and giving a lower value, so it wasnot triggering the P0420 (similar to plug fowler trick)
Once the Cat guts completely disapeared, it no longer had the P0401 code problem but up pops the P0420 as the rear02 sensor is now able to read full oxygen flow

 

I just re-read that in a "Sheldon" voice! Awesome! Good luck and hope that code doesn't come back.

 

I simply bought a new front 02 sensor and put a thinwall brass tubing sleeve over the rear 02 sensor until I save up for a new cat.
It runs perfect that way and fuel trim looks perfect on the scanner.
If it defies Federal Law that is another huge bonus.

 

The EGR temp sensor isn't used by the ECU to control the EGR system. It is only used as a test to be sure the system is working. It's not used as feedback like how the front O2 sensor data causes the ECU to adjust fuel ratio. The EGR temp sensor and back O2 sensor are only used as tests to check that things are working correctly.