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I bought the car 2 years ago and I've been having issue with the engine. Soon after buying the car this P0420 popped up. Losing oil somewhere and it wasnt smoking or leaking either. Replace the radiator because the tank busted open. Then engine was making a lot of knocking noises barley made it home. There it sat for 2 years then I replace the engine just the block from a junk yard. Replace the engine without difficulty started up and ran good with no problems. I had bought a used catalytic converter and it looked good inside, honey comb was intact. The original cat had a hole in the honey comb so I figure that is why I got the P0420 2 years ago.
Last week this P0420 showed its ugly head again. When idling and warmed up I notice the short and long fuel trim is reading negative, short term between -4 and -2 and long term always reading around -8 and -4. The O2S1 is switching back-and-forth and O2S2 is holding steady around 0.080 and 0.100 volts. After driving for several miles the O2S2 will start to mimic O2S1. At highway speed the short term fuel trim is showing positive and negative on long-term fuel trim. Leading me to think the cat is bad, but I'm not convinced yet.
I'm exploring the possibility that the injectors are leaking causing the negative on short term fuel trim and excess unburt fuel in the cat that will produce the P0420. I measure the resistance on the fuel injectors and all of them read about 17 ohms. The service manual states it should be between 12.1 and 12.9 ohms. I have removed the injectors and fuel rail from the intake manifold to see if they are leaking when the system is primed and they are not. My next step is to crank the engine and see if they leak after the Engine has stopped.
I'm at a complete loss and I have no idea what to do next. How can I make sure the cat is actually dead. If I replace it will the cat go bad again? Is there physical signs that I can check on the cat? Is the fuel trim behaving correctly?
Good morning jbr7195,
I see a lot of these cars. They have some pattern failures, like anything really, and cats and engines are at the top of that list.
The p0420 catalyst efficiency code area when the downstream O2 mimics the upstream, like you witnessed in the data stream.
That's all I need to call a bad cat in my experience.
The fuel trims sound pretty close to normal. The rule of thumb is a combined 10 + -is considered within normal range. For example, if ltft is 7 and stft is 3, you're in fine shape.
Considering all the injectors ohmed the same, I wouldn't be very concerned just yet that they don't reflect the service information.
I think you would be seeing more positive fuel trims than you have if there was an injector leaking, and probably some other driveability issue too.
Hope this helps.
The answer to that depends on your local laws, some jurisdictions require type approved cat for that particular vehicle. I know where I live in the UK there has been a tightening up of the rule because of problems with cheap cats, approved cats generally last much longer than the cheapest unapproved cat which can often fail a tail pipe test after only a year.
P0420 with no oxygen sensor or misfire codes is pretty well always a cat issue but one question in my mind is the coolant temperature normal when crusing.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
I agree wit Noah. The data you're describing suggests a bad cat.
I dont recommend cheap converters from ebay. In my experience cheap converters tend not to last.
also make sure its the proper cat for the car, If you were to use a federal cat on a california car it could potentially set a cat code.
Not sure on Altimas but I've seen failed cats destroy motors. The pieces of cat get drawn back into the engine and act as an abrasive and start them burning oil. I'd suggest your old engine was burning oil even though there was no visible smoke but the cat may have been the cause, not the result.
Is suggest biting the bullet and buying a new quality cat otherwise you're simply going to continue the cycle of throwing expensive parts at this car. Just my opinion.
I think the Altima won't be so prone to chunks of cat getting back into the engine but more recent engines with very close coupled cats such as the 3 cylinder Toyota I was checking over last it is a real danger.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
If I remember correctly the Altima's were having a problem with the cat's breaking apart and being sucked back into the combustion chamber thru the Exhaust valves during valve overlap from the variable valve timing. Which caused scoring in the cylinder walls, which in turn caused oil burning.,
Like others have said , it appears you have a failed Catalyst and remember, you get what you pay for and cheap doesn't always mean less expensive.
"Silver bullets are for killing Werewolves, not fixing Cars." -Rob Longoria-
Toyota I was checking over last it is a real danger. 