Plugs don't look too bad. Also check your wiring loom going to the O2 sensors. The front driveshaft wore a hole in mine and then through one of the wires on my left rear O2 sensor. Caused a different code but I searched for the issue for a couple months and finally found it about 2 feet up the wiring loom.
Ugh, P0420 on my 2nd set of cats
- Thread starter Mr T
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Plugs don't look too bad. Also check your wiring loom going to the O2 sensors. The front driveshaft wore a hole in mine and then through one of the wires on my left rear O2 sensor. Caused a different code but I searched for the issue for a couple months and finally found it about 2 feet up the wiring loom.
michiganlebnani
Member
It looked ok when I first looked at it, but I can do a trace again based on your inputs to make sure and see. Thanks
No problem. Hope it all works out. Chasing codes is a pain.
If the exhaust system has air leaking, the check engine light could be triggered off with code P0420 and P0430.
The cheap fix procedure for code P0420 and P0430 is removing exhaust manifold, cleaning the math surface, and replacing exhaust manifold gasket with new ones; also, cleaning the mate surface & installing new doughnut gaskets between the flanges at exhaust manifold and catalytic converters.
The cheap fix procedure for code P0420 and P0430 is removing exhaust manifold, cleaning the math surface, and replacing exhaust manifold gasket with new ones; also, cleaning the mate surface & installing new doughnut gaskets between the flanges at exhaust manifold and catalytic converters.
A couple of the plugs looked pretty dark from what I could see but if you just changed them all that takes care of that. When you go to have the cat involved, and I'm addition it's the type needing welding, ask them what they think. Since you're paying for shop time it might be worth having new exhaust gaskets with you if they're gonna have the manifold off anyway. I feel for you man. This stinks. I can't remember but along the way the gas cap was checked too, right? If this continues I'd really consider paying the shop fee of someone you trust to tell you what's happening. As long as they don't say that's normal it'll save you some gray hair if nothing else.
michiganlebnani
Member
Got the Magnaflow CAT in the mail this week and got it installed this morning. Erased the P0420 code drove around and so far didn't came back. The Muffler Man mentioned something regarding aftermarket universal CATs as they tend not to last like the original OEM. He said the filaments on the inside of the CAT tend to degrade over the years and especially if you live in a cold environment. I am not sure how accurate his feedback is but anyway will see what happens.
With a new set of plugs, wires, O2 Sensors and a new MF CAT .... should be ok for now.
With a new set of plugs, wires, O2 Sensors and a new MF CAT .... should be ok for now.
PLEASE keep me posted on your progress. I'm curious to know what you find.
Thanks for everyone's thoughts here. I've been doing a LOT of reading and boy this is a learning process. Below is a link all of us (who actually care to know what is going wrong) should read. Bottom line, seldom is it CAT failure. Most often engine issues are causing the failed CAT (i.e. bad particles sent downline from the motor damages or destroys the CAT over time. Ugh. Not easy to find those.
Check this link
http://www.easterncatalytic.com/education/tech-tips/the-misleading-nature-of-the-po42o-code/
By the way, a bit more facts for those of you wishing to know and who actually care.
Yukon has 144K as I originally posted. I replaced plugs and wires at about 120K. Air filter is clean.
HOWEVER, this motor does an odd thing that I really am baffled about--and I struggle to repeat what it is. Let me try to explain it and tell me if you've heard of this before.
Again, can't repeat it at will all the time--but when the motor is downshifting, say up a slight grade and I give it a bit more gas, just when the pause happens in shifting and the revs are about to jump, you hear the "PHHHHHIT" sound. Take your lower lip and cover half of your top teeth and blow hard. You'll make an odd air noise. The motor will sometimes make that for only about .25 of a second. My wife has looked at me with that "what was that face" several times and I've often thought it sounded like exhaust just blew back "somewhere". I know a great deal about engines and can't imagine where blow back would happen--nor how. I don't consider it an exhaust leak because I would hear and exhaust leak all of the time--and not only on rare occasions....RIGHT?
TKH
Yukon has 144K as I originally posted. I replaced plugs and wires at about 120K. Air filter is clean.
HOWEVER, this motor does an odd thing that I really am baffled about--and I struggle to repeat what it is. Let me try to explain it and tell me if you've heard of this before.
Again, can't repeat it at will all the time--but when the motor is downshifting, say up a slight grade and I give it a bit more gas, just when the pause happens in shifting and the revs are about to jump, you hear the "PHHHHHIT" sound. Take your lower lip and cover half of your top teeth and blow hard. You'll make an odd air noise. The motor will sometimes make that for only about .25 of a second. My wife has looked at me with that "what was that face" several times and I've often thought it sounded like exhaust just blew back "somewhere". I know a great deal about engines and can't imagine where blow back would happen--nor how. I don't consider it an exhaust leak because I would hear and exhaust leak all of the time--and not only on rare occasions....RIGHT?
TKH
michiganlebnani
Member
Great thanks for sharing Mr T. i will keep you posted !
First off I'm glad the code went awa y. But I'm sorry you had to do all of that, You've done a good job keeping everyone posted on your progress. The sound you're describing sounds like a cracked or loose vacuum line. I can't recall your year model or if you've done any mods that require vacuum. Most of today's new cars don't have many vacuum lines. Hitting the gas pedal obviously creates more vacuum but it sounds like something on the top end. Could be as simple as your charcoal canister or even your overflow/fill tank as the extra revs will certainly make more vacuum. Please keep us posted on what you find.
