6G Celicas Forums

Last summer the first catalytic converter melted and clogged the second one. I punched out the second and replaced the first one since that is the one with 2 oxygen sensors connected to it. Since I replaced the cat I've put about 20K miles on my car. The cat. melted and got clogged again.

Does anyone know any reason(s) why this is happening?
-220K miles (2.2L)
-Engine is running at normal temp, never over heats
-Doesn't burn hardly any oil, maybe half a quart every 3,000 miles.
-It is eating gas, though i think that was from the cat being clogged and it needing extra to keep the engine running under the increased back pressure from the clogged converter.

Here is a pic of what it looked like before I punched it out today

I'd guess that eating gas is the cause of the dead cat, not the other way around. Running rich will kill a catalytic converter. Is your check engine light on? I would guess that the primary O2 sensor is bad, causing the car to run rich which kills the cat. Which probably throws another code from the second O2 sensor.

The engine light has never been on. I just went out and checked for codes, there aren't any codes. The engine light flashes quickly when I bridge the TE1 and E1 terminals.

call animal protective services, he keeps killing cats!!!!!


just put a straight pipe there dude.

The extra fuel is not being burnt, it is going into the exhaust and burning when it hits the superheated surface of the catalytic converter. This causes the catalytic converter to melt. Replacing the catalytic converter will result in the destruction of the new catalytic converter. Fix the excess fuel problem before you worry about anything else.

Lol you could always buy an oxygen sensor simulator("off road use only" of course) so that you can delete the cat and second O2 sensor. Maybe $60-$150.

PRECISELY. You need to know why you're running so rich. Bad sensor, bad plug wires, plugs, cap, rotor, weak coil, low compression, leaky injector, etc etc. That is 100% fuel damaged catalyst there. Classic melted.

Thanks for the responses

Things I know aren't wrong with the car (done or checked recently)
-Wires
-Plugs
-Compression
-rotor
-cap

Things I think could be wrong
-Air intake temp sensor
-Bad oxygen sensor, but this would send a code and there aren't any codes.
-Bad injector

How do I check the oxygen and mass airflow sensors. I assume if they are weak, not bad, they can still throw off the air fuel mixture.
Anyone know what the resistance specs are for these sensors?

This post has been edited by barterj: May 20, 2012 - 7:12 PM

Air intake, not gonna affect the afr enought to cause that
O2, good possibility. can go bad w/o throwing a code.... i had one go bad and lean my 7a out into the 18+ to 1 area without a code...

injectors are another good possibility... but an O2 sensor is more likely.. and should be replaced every so many miles.. probably well overdue anyway..

Thanks for that info stephen_lee. Now I get to figure out which one it is that's bad. Where I have the cali emissions 5s-fe I have 2 oxygen sensors. Does anyone know the resistance specs for the oxygen sensors for the 5s-fe?

you don't measure resistance, you watch the sensor switching which it won't if you're running rich. Check for high fuel pressure and see if you can borrow a scan tool to see what your long and short term fuel trims are. I don't think you have a MAF sensor. Does the engine ever stumble or stutter or run rough? That's classic engine misfire damage or just very very rich.

you should invest in an A/F gauge. even if it is stock, it always helps to have a constant check on how your car is running.

yea you dont measure resistance of the o2... and its the precat o2(first one, in the exhaust manifold) that will affect afrs.. the post cat (further down the exhast stream) is to make sure your cat is working

I curious what your cat looked like from the exhaust end.

I pulled mine off and the engine end looked fine but and the exhaust end looked like this

The engine has only ever run rough at start a few times. All of which were after I didn't use the car for a few days and it rained a lot. But I comes right out of it within 500 ft of driving. Other than that I've never had idle issues. OBD I scan tools are almost impossible to find and far too expensive for me right now.

Is there another way to measure the fuel pressure, other than with a scan tool?

I should be able to measure an aspect of that sensor to see if it's working properly, whether it be resistance or voltage from the sensor. I just read some articles about O2 sensors and all but one said that the O2 sensor has a voltage that ecu uses to determine the mixture of the air and fuel. I'm going to assume that it's dead if I have no voltage from the sensor.

Does anyone happen to know the voltage specs of the first O2 sensor? I'm guessing it's a slim chance of anyone knowing this

This post has been edited by barterj: May 24, 2012 - 10:05 AM

id just replace it unless it already has been on the last 50 000 miles

"Normally, the lifetime of an unheated sensor is about 30,000 to 50,000 miles (50,000 to 80,000 km). Heated sensor lifetime is typically 100,000 miles (160,000 km). Failure of an unheated sensor is usually caused by the buildup of soot on the ceramic element, which lengthens its response time and may cause total loss of ability to sense oxygen. For heated sensors, normal deposits are burned off during operation and failure occurs due to catalyst depletion. The probe then tends to report lean mixture, the ECU enriches the mixture, the exhaust gets rich with carbon monoxide and hydrocarbons, and the fuel economy worsens."

Sometimes it doesnt hurt to bite the bullet and pay toyota to do a real diagnostic checkup on the car.