# 2003 vq35de..pre cat failure?



## Nickaltima (Jan 11, 2008)

i put my headers in today..annnd when i took the front cat off part of the screen was missing not completely tho like not all the way through..i dnt have any symptoms of the p.c failure THANK GOD and im so glad i caught it sooner then later lol..but on the other side of the spectrum woooooow what a dif in performance and sound with not even being tuned..i cant wait to get a reflash..i reccomend everyone with a altima...replace your headers and save yourself the aggravation and stress/money and put a set of A/M headers in..F the epa=D


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## Altima SSS (Oct 10, 2007)

How many miles on your Altima? Yeah, even the 3.5s are susceptible to pre-cat failures it seems ... not as prevalent as the 2.5L, but is does happen with the 3.5s also.

How hard was it to put headers on the VQ? What did you do about the O2 sensors not seeing a pre-cat anymore?


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## Nickaltima (Jan 11, 2008)

i bought it with 60k and its got almost 125k on it now..umm it was actually really a pian in the ass to put them on everything was rusted bad i had to cut the downpipe from the manifolds...the manifolds themselves went in easy and came out easy..a cpl brought the stud out with the nut..no big deal tho at least they didnt break lol...and the downpipe didnt line up with the manifolds i had to use a jack to put pressure on it to get them close enough to get the bolts in..but as far as the cel issue i used simulators and they worked perfect....the headers i put in were hotshot with a high flow cat..they retail at 700+ship but i found an amazingggg deal=X..i wouldnt really recommend the ebay ones b/c a buddy of mine got them for his alty 3.5 and they are chinsey metal like half the weight of mine..i would go with obx at the least..but i just beat a SL 500 by 2 or 3 cars and thats un tuned i cant wait to get a tune=D


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## Altima SSS (Oct 10, 2007)

The pre-cats lasting 125K isn't bad I guess, as I can't see them lasting forever in the harsh environment they are in. I bet other vehicles with pre-cats that close to the heads have issues with high mileage too. A lot of it probably depends on how hard the engine is ran also ... I can see pre-cats degrading faster on an engine ran hard a lot of the time vs. one babied most of the time.

Guess I'm not up on the tuning requirements on the VQ after doing intake or exhaust mods, but I was under the impression that since it has an air mass sensor that the ECU would self adjust ... at least in the closed-loop running conditons.

Does the ECU need to be reflashed/tuned for the open-loop wide open throttle running conditons?


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## Nickaltima (Jan 11, 2008)

i wish my car would self adjust lol..ive heard a couple people think that it does that..the ecu needs to be tuned or reflashed b/c it still thinks everything is stock..im sure it adjusts to a certain extent with the MAF but nowhere near what it would after a tune..you have to adjust the A/F ratio's and the timing..ive got a full exhaust with hotshot racing headers and magnaflow catback a cold air intake, front and rear motor mount inserts(drastic improve on takeoff and shifting in my manual tranny)..i might drop it and get the reflash and call it a season for this year..as you prolly already know our cars dnt get modded that much so parts are expensive as hell still


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