# 2002 2.5S Low power/bogging down before downshifting



## JP11283 (Sep 29, 2012)

I've got a 2002 Altima with 126,xxx miles on it with a few problems I wanted to get some opinions on, especially after reading about all the problems with 2002 2.5 Altimas.

I had an intermittent check engine light problem that started about four or five months ago. I was finally able to get it looked at about a month ago. It was throwing a P0421 (catalyst efficiency below threshold) code. The whole time I was having the check engine light problems, the car would bog down down before it would downshift when moderately accelerating to pass someone in city traffic or on the interstate. Our mechanic replaced the radiator side converter, which fixed the check engine light, but not the bogging and general lack of power. 

Fast forward a few weeks, and now the check engine light's on again. It's throwing P0138 (O2 Oxygen Sensor Circuit High Voltage (Bank1, Sensor2)) and P1456 code (EVAP Emission Control System Very Small Leak (Positive Pressure Check). It's bogging down even more lately and just seems to have very little power. Yesterday I had to completely floor the accelerator taking off from a stop light to keep up with traffic. I'm also getting a lot of knocking during the first ten or so minutes driving in the morning, even though there is plenty of oil in the car. After hearing about the problems with catalytic converters on these cars, and knowing that I didn't get it fixed for quite some time, I'm a little worried. The car doesn't seem to be burning any oil, but I wanted to see what everyone's opinions were. 

I'm also having problems with the transmission flaring and squeaking between the second and third gear shift, though the transmissions shop said it's not quite ready for a rebuild yet, but will need one in the future. They also said the bogging isn't related to the transmission in any way. Thanks for your help!


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## JP11283 (Sep 29, 2012)

Bump to see if anyone might have any ideas.


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## FriendlyNismoTech (Oct 28, 2012)

Well based on the information you're giving and the description of the issue I would say either your main catalytic converter is plugged up or nearly plugged up or your second converter is "often referred to the resonator". Now this can be catastrophic to the QR25 engine, these engines do not use an EGR system "exhaust gas recirculation" instead they open the exhaust valves during the intake stroke to suck some exhaust back in to reburn it. Now when the catalytic converter fails it can break up, and this debris can get sucked back into the engine which will quickly destroy the walls and rings of the engine. I had a customer in August that came in for an SES light. I confirmed his converter was in need of replacement and that his rocker cover was leaking. He opted to only replace the rocker cover "valve cover". 3 weeks later the same vehicle was towed in, he had only put 700 miles on it and his converter had broke apart and destroyed the engine. A used QR with decent mileage will cost you around 2500 installed depending on your area, versus a 600 dollar cat and 2hours of labor.


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## JP11283 (Sep 29, 2012)

I had a P0421 (catalyst efficiency below threshold) code for a few month when the bogging started. I had the converter that's part of the manifold replaced. My mechanic said it had a leak, but didn't mention anything about the internals being bad. Replacing it fixed the P0421 code, but didn't make it run any better. I've been keeping an eye on the oil since replacing the cat but haven't noticed any oil consumption whatsoever.


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## smj999smj (Jan 1, 2006)

I would get an exhaust backpressure tester and test for a restrictive exhaust. This will confirm or deny any chance of a clogged converter.


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