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Discussion Starter · #1 ·
Lots of questions, so brace yourself! I just bought an '07 Spec-V last saturday, and while out driving it around, the SES light came on. Hooked up my OBD-II interface and pulled both P0420 and P0430. After reading up on it, I nearly crapped my pants thinking my motor would be wasted, until I realized it had OBX headers on it with no precat (PHEW!!!!). From what I can tell, this is the kit I have on it:



It looks like everything after the flex pipe is stock. Does it still have a cat downstream? All I can see from the part numbers and service manual is "Front Muffler" and "Rear Muffler". Any recommendations for upgrading the rest of the exhaust system? Where should I start with eliminating the codes?

The exhaust smells really rich, and I'm getting pretty lousy gas mileage (I've been trying to keep the tach around 2k driving around town and I've been averaging about 16mpg). In addition, when getting on the highway, I'm having a heck of a time accelerating (acc pedal to the floor, 5th gear, ~50mph the tach pegs out at about 3500rpm, and it'll start bucking a little if I don't ease off the acc pedal).

I've read about the knock sensor mod, and think I might try that as soon as I can eliminate gas as the issue (Like a dummy, I filled up with regular unleaded before I noticed the "Use Premium Only" sticker). Thoughts?

Thanks guys! I already love this car, and really want to get her in tip-top shape again.
 

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09 Altima 3.5SE 6MT Sedan
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Geez, 3 days and 3 spec-V's with major engine probs...must be Sentra Season.

Can your OBD reader get live stats on short and long term fuel trim %'s? That's a pretty good debug technique for vacumn leaks (not if you are running rich), bad/missing O2's...a possibility.

Pretty sure the 0420 code is cat efficieny...there are two other users posting this week about precat issues...which you don't seem to have...so in your case, might be you just need some anti-fouler extenders and new O2 sensors....assuming you have bung holes in those headers to put them in.

Next question is why those headers were put on...ie had precats failed previously? But like the rest of us...it will take some time to figure out what state your pre-enjoyed Nissan is actually in. FWIW I finally had my compression tested this year....freakin' nail biter time that was.
 

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Discussion Starter · #3 · (Edited)
Good point, it's at 120,000 miles. It looks like the headers have been on there quite a while (they were wrapped in fiberglass which had become brittle and started kind of shattering, so I just removed the wraps), but I'll check the compression when I change the fluids tomorrow. Are the compression pressure #'s different for the spec-v from the numbers for QR25DE in the service manual, since it has a higher compression ratio?

My OBD-II reader is a USB interface, and the software has PID monitors and data loggers, so I'll try to get some logs.
 

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Discussion Starter · #4 ·
Checked the compression today when I changed the oil, and got a solid 195 out of each cylinder (the FSM lists 181 as standard for the 9.5:1 motor, so I'm guessing the higher value is due to the higher compression ratio of the spec-v?), spark plugs looked clean, and I drained out 5 qt of oil, so looks like I got lucky on that front!

I haven't had a chance to log fuel trims, I'll try to do that tomorrow.
 
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