$275 '00 Lexus ES300--P0420

[TXCarGeek]

Originally Posted by Mad_Hatter
Originally Posted by TXCarGeek
Well, drove it around some more today and the fuel trims seemed okay. At idle, they were all under 4.0. I cleared the code yesterday and I'll see if it returns.

I did notice though that past 4k rpms, it seems to really not want to rev out freely. I have a friend of mine with a muffler shop so if the light returns, I'll take it to him and have him test to see if the converter is actually clogged.




Big improvement and more where they should be.ðŸ‘


The code came back as pending so far...i'll see if it sets off the light again. I at least know there isn't a a vacuum or fuel delivery issue with the fuel trims looking better.

Also, checked resistance on the upstream A/F sensor for good measure and they came back within spec. As for the downstream O2 sensor behind the cat, voltage generally was bouncing from 0.1 to 0.9, although I didn't think it was acting strange, but I'm not 100% knowledgeable when it comes to o2 sensor behavior.

Edit: just went for a drive and while the downstream sensor sometimes does fluctuate back and forth between 0.1 and 0.9, other times it does not fluctuate at all and stays around 0.6. The graph it gives is not at all consistent. Would it be giving strange readings because the cat is clogged or would it still fluctuate between high and low regardless of cat function?

 

[clinebarger]

The VVT 1MZ/3MZ really come alive in the upper revs WHEN/IF they can breathe!
Check the 2 dashpots in the Intake Tract as well, They should actuate & hold vacuum with a hand pump!

 

[Mad_Hatter]

Originally Posted by TXCarGeek
Originally Posted by Mad_Hatter
Originally Posted by TXCarGeek
Well, drove it around some more today and the fuel trims seemed okay. At idle, they were all under 4.0. I cleared the code yesterday and I'll see if it returns.

I did notice though that past 4k rpms, it seems to really not want to rev out freely. I have a friend of mine with a muffler shop so if the light returns, I'll take it to him and have him test to see if the converter is actually clogged.




Big improvement and more where they should be.ðŸ‘


The code came back as pending so far...i'll see if it sets off the light again. I at least know there isn't a a vacuum or fuel delivery issue with the fuel trims looking better.

Also, checked resistance on the upstream A/F sensor for good measure and they came back within spec. As for the downstream O2 sensor behind the cat, voltage generally was bouncing from 0.1 to 0.9, although I didn't think it was acting strange, but I'm not 100% knowledgeable when it comes to o2 sensor behavior.

Edit: just went for a drive and while the downstream sensor sometimes does fluctuate back and forth between 0.1 and 0.9, other times it does not fluctuate at all and stays around 0.6. The graph it gives is not at all consistent. Would it be giving strange readings because the cat is clogged or would it still fluctuate between high and low regardless of cat function?


In a system where everything is working properly (FI, o2 sensors, catalyst, no contaminants entering exhaust stream) the downstream should read around .5v, maybe a little more or little less. More importantly it should be steady. That's because a properly functioning Cat is filtering the air and filtered air is what the post o2 should be seeing. Your rpm's should not change the downstream voltage in a significant way, unless the Cat is not up to task in filtering (burning off) the increased gasses or unburnt fuel in the case of a misfire. Habitually rich exhaust or contaminants like oil can cause the cat to run hot and die prematurely. In theory Cat's don't die on their own, their fouled up and killed by some other condition in the engine.

Considering the age of the vehicle, the history of misfiring and the way your downstream sensor is erratic... that right there, for me, puts the catalytic converter as the culprit of your p0420. That's what I would check next.

 

[TXCarGeek]

Originally Posted by Mad_Hatter
Originally Posted by TXCarGeek
Originally Posted by Mad_Hatter
Originally Posted by TXCarGeek
Well, drove it around some more today and the fuel trims seemed okay. At idle, they were all under 4.0. I cleared the code yesterday and I'll see if it returns.

I did notice though that past 4k rpms, it seems to really not want to rev out freely. I have a friend of mine with a muffler shop so if the light returns, I'll take it to him and have him test to see if the converter is actually clogged.




Big improvement and more where they should be.ðŸ‘


The code came back as pending so far...i'll see if it sets off the light again. I at least know there isn't a a vacuum or fuel delivery issue with the fuel trims looking better.

Also, checked resistance on the upstream A/F sensor for good measure and they came back within spec. As for the downstream O2 sensor behind the cat, voltage generally was bouncing from 0.1 to 0.9, although I didn't think it was acting strange, but I'm not 100% knowledgeable when it comes to o2 sensor behavior.

Edit: just went for a drive and while the downstream sensor sometimes does fluctuate back and forth between 0.1 and 0.9, other times it does not fluctuate at all and stays around 0.6. The graph it gives is not at all consistent. Would it be giving strange readings because the cat is clogged or would it still fluctuate between high and low regardless of cat function?


In a system where everything is working properly (FI, o2 sensors, catalyst, no contaminants entering exhaust stream) the downstream should read around .5v, maybe a little more or little less. More importantly it should be steady. That's because a properly functioning Cat is filtering the air and filtered air is what the post o2 should be seeing. Your rpm's should not change the downstream voltage in a significant way, unless the Cat is not up to task in filtering (burning off) the increased gasses or unburnt fuel in the case of a misfire. Habitually rich exhaust or contaminants like oil can cause the cat to run hot and die prematurely. In theory Cat's don't die on their own, their fouled up and killed by some other condition in the engine.

Considering the age of the vehicle, the history of misfiring and the way your downstream sensor is erratic... that right there, for me, puts the catalytic converter as the culprit of your p0420. That's what I would check next.



Thanks for the input so far. I'm back home some time next week and I'll have my exhaust guy take a look at things.