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Car missing

I have a 2005 Nissan Altima 2.5L 4 cylinder. About a month ago I had check engine light come on and required to replaced the catalytic converter. I replaced it myself with one from Autozone. Now 2 weeks after replacing it; every now and then I’ll be driving let off the gas and when I get back on the gas the car starts missing. It has happened several times in the last few days. The car does smooth out after a few seconds but is a hassle and a worry. What else could be wrong?

First have the fault codes sownloaded and post them here.

And I have a few questions:
was the upstream oxygen sensor replaced when you replaced the cat converter?
was the aftermarket converter a “direct fit OEM replacement” or a generic converter?

“About a month ago I had check engine light come on and required to replaced the catalytic converter.”

Who made that determination (converter replacement necessary)?

There are currently no codes. I did not replace any sensors when I replaced the Catalytic Converter. This car has 2 Catalytic converters and the one that needed replaced was manifold style. Meaning it bolted directly to the block. It was a direct fit made by walker, not OEM. After the light came on I went to Autozone and they said that’s what it was. I then took it to the Nissan dealer and they confirmed the issue. They stated that the through-put for the converter was a 3 on a scale of 1-10. 0-being stopped up completely and 10 being completely open.

The converter was a result of the problem, not the cause of the problem. You need a prper analysis for a proper repair.Bad o2sensor, bad injector or bad pcv valve come to mind, how long since your last air filter?

How many miles are on it? How old are the plugs & wires? Fuel filter? Has anyone ever looked at the fuel pressure? Now would be a good time. Do you keep track of the gas mileage & if so, how has it been?

Taking the sputter + a partially plugged cat I’m wondering mostly about excessive, unburned fuel leaving the engine - poor spark or running too rich from a bad fuel pressure regulator, injector, or coolant temp sensor.

Why did you not get an OEM cat? Should have been replaced under warranty.

I Agree With Waterboy That "The converter was a result of the problem, not the cause of the problem. You need a proper analysis for a proper repair."
The converter possibly did not need to be replaced.

Lots of things can trigger converter codes. I have personally seen a situation in which a code for catalyst defficency was set and no other clues except intermittent stumbling/hesitation (miss ?) when getting back on the accelerator. Turned out to be an intermittent TPS (throttle position sensor). Because of the nature that TPSs wear out and the way they operate, a TPS code won’t always be present. A scan tool can display sensor data that would properly diagnose a worn TPS.

I’m not saying that this is what’s wrong with your car, but rather illustrating with an example, why the car needs proper diagnosis. Codes don’t always tell which parts to replace, nor do they always indicate which ones do not need replacement. In the example above, a loose TPS, TPS connector, or bad wiring could have been the culprit.


I Don’t Know Nissan From Shinola.
Do You Have A SULEV (California Emissions Specs - Super Ultra Low Emission ) QR25DE Engine ?
Was It Code PO420 ?

A 9 page Nissan TSB (06/12/09 technical service bulletin NTB09-046) for some (check VIN) 2004 -2005 Altimas with those specs does specify replacement of not only the cat, but also the exhaust manifold, gaskets, etcetera.

The ECM has to be reprogrammed as part of this TSB.

I don’t know if this applies to your vehicle, possibly checking your vehicle against the TSB would be beneficial.


The car has 86,000 miles. I’m not sure on the plugs, wires or fuel filter. The car and part is out of warranty. The car has been getting about 25-26mpg with a lot of city driving and idling. The car did not miss before replacing the catalytic converter.