2010 Nissan Altima 2.5
I was driving and it started losing power then started to hiss from under the car. Thank The Lord i was close enough to make it home. About a month ago a friend did a test on it and he said the cats were clogged and needed to be replaced soon so i figured that was my issue now. I changed out both cats, the upper and the lower flex pipe. The honeycomb in the lower cat was busted up and falling out when i took it off the car. The hissing was from the pipe too, i guess it had a crack in it under 1 of the heat shields. I changed out both oxygen sensors as well. It sounded fine for the first 10 mins or so after i cranked it and let it burn off all the oils from the new parts. Then it started to miss and sputter again. I drove it around and it was doing the same as before just not as bad. It sputters and does a nose dive when i accelerate. I have to play with the pedal and accelerate then let off then accelerate again etc., for it to go anywhere. Any ideas what this could be? The plugs, coils, valve cover and gasket have been replaced recently, maybe within the last 6 months or so. My obd2 scanner has codes P1148, P0300-random multiple cylinder misfire, P0138-oxygen sensor 2 bank 1, P0037, P0031-oxygen sensor 1 bank 1, P0301 cylinder 1 misfire. I have a 2006 Infiniti that is doing the exact same thing. The cats were replaced, oxygen sensors replaced, plugs replaced and still getting the same codes.

The P1148 is a generic "screwed up mixture" code and is a symptom and not a problem, but the specific misfire on #1 could indicate a big problem. Have you checked compression on the engine? If not, do so before you go any further. QR25's are "Miller cycle" engines and will inhale pieces of a disintegrated catalyst. The liquid metal scrubs-out the rings and cylinder walls almost instantly, basically turning the engine into junk. So do a compression check and see what the verdict is.

If the compression is still okay, did you put in aftermarket A/F (front O2) and HO2S (rear O2) sensors? If so, that's a mistake. The front A/F will cause all sorts of crap-running and mixture issues, and for the most part aftermarket ones never work right. If you still have the original, try reinstalling it. You may have bunged a connector or wire during the install anyway, because the P0031 is for the A/F heater circuit and not the sensor per se. With the HO2S you may get away with aftermarket but could end up needing a spacer, depending whether you bought a cheap cat or a good one.

VStar650CL wrote: ↑

Fri Jan 07, 2022 12:45 pm

The P1148 is a generic "screwed up mixture" code and is a symptom and not a problem, but the specific misfire on #1 could indicate a big problem. Have you checked compression on the engine? If not, do so before you go any further. QR25's are "Miller cycle" engines and will inhale pieces of a disintegrated catalyst. The liquid metal scrubs-out the rings and cylinder walls almost instantly, basically turning the engine into junk. So do a compression check and see what the verdict is.

If the compression is still okay, did you put in aftermarket A/F (front O2) and HO2S (rear O2) sensors? If so, that's a mistake. The front A/F will cause all sorts of crap-running and mixture issues, and for the most part aftermarket ones never work right. If you still have the original, try reinstalling it. You may have bunged a connector or wire during the install anyway, because the P0031 is for the A/F heater circuit and not the sensor per se. With the HO2S you may get away with aftermarket but could end up needing a spacer, depending whether you bought a cheap cat or a good one.

Thanks for the info. I haven't done a compression check on them but I'll do that soon. Yes I did put aftermarket sensors on there. I got them on Ebay. If the compression is ok then i'll buy some oem sensors and hopefully that'll be the only issue.

This post on another site has some great pics of what "cat inhalation" did to a QR25 Altima:

https://grassrootsmotorsports.com/forum ... 366/page1/

The guy looking at my Altima is telling me that it stops missing and sputtering when he puts the transmission in manual mode. He says it drives fine that way but when he puts it back in drive, it misses and wont accelerate again. He's saying that its the valve body in the trans. I hope that's it but I don't see how that would cause it to miss, especially when its in park?