Apparently a cutout CAN affect a tune!?
05-08-2008, 01:08 AM
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Apparently a cutout CAN affect a tune!? Gents,
Okay, this post will be long, but please bear with me. First off, a little bit of history. All the bolt-ons in my sig were installed a few months ago. After the cutout in my exhaust, the factory Z28 dual setup is still mounted. When I got my tune done with HP Tuners, it was decided that we tune with the cutout closed; afterall, it WOULD be annoying as hell to go through the lengthy process of tuning while making all that damned racket.
So, the tune was done, and goodness gracious the Z sure did scream! We drove around for a half-hour to monitor the long-term values in the PCM. All was well, and so the tuner headed back home. Well, me, being the V8 sound-lover that I am, open the cutout and have driven it that way ever since. The SES light came on the day after the tune. I got the codes pulled, and they were P0172 and P0175 (Banks 1 and 2 System Rich).
Well, after discussion with my tuner and countless numbers of other LS1 folks, it was concluded that my 02 sensors suck, being the product of an LS1 with 94,xxx miles. BUT...In the time between the tune and now, I had rendevouzed with my tuner yet again so he could try tweaking some more, just in case the codes were a tuning issue. I closed the cutout, and we began the tune. Tune done, long term values evaluated, everything fine, car screams again, tuner goes home. So, yes, you guessed it, I open the cutout again. The same exact thing happens. SES comes back on the next day.
I got the codes pulled again, same issue, system rich. This time, a new person at AutoZone pulled the codes, and her first response was "Uh oh, time for new oxygen sensors!" Now, after hearing that same O2 theory over and over, coupled with AutoZone Girl's initial response, I must admit to having a reassuring sense that my problem could be solved by one simple purchase of new O2 sensors.
Now, besides the stupid SES light, I must go into detail about the performance-hindering symptoms. Vaguely described, with SES on, under WOT the car simply wouldn't respond like it did right after the tune. Moreso, in 5th gear at specifically 70ish MPH, you could floor it, and nothing would happen. The car would sorta have a "shuddering" event in which, as long as I had the throttle mashed to the floor, it would seem as though the PCM was pulling timing, or perhaps severely leaning the A/F mixture. It simply wouldn't accelerate. Also, it seemed to do the same thing, though less exaggerated, at high RPM in other gears. I know what you're thinking..."dirty MAF." Keep reading.
Now to the strangest part: For the past few weeks, I have been thinking about my situation, mostly while under the influence of mankind's best friend, beer. I thought about how, seemingly coincodentally, my car screamed like a banshee with a closed cutout after PCM flashes, yet upon opening the cutout afterwards in both instances, it was the same old story. So, last week, I closed the cutout. Immediately I'm disgusted by the factory sound, courtesy of the bathtub-sized factory muffler. Regardless, I head to Wal-Mart for some groceries, and would you believe, the goddamn SES goes off. I'm totally perplexed, because the theory of the cutout being the problem was disspelled by everyone I know, including LS1techers who responded to my numerous threads concering P0172 and P0175.
I do my shopping in Wal-Mart, with the car situation in the back of my mind the entire time. I get back in the car, crank her up, SES is still off. I start driving back to the bachelor pad, and LOW AND BEHOLD, all my power has been restored. No more sluggishness at high RPM, no more restricted acceleration in every gear, and a just a general feeling of restored performance. Gentlemen, can anyone out there explain this to me!? How can this be? It's almost as if the PCM was treating the cutout as one huge exhaust leak, triggering those system rich codes!? It has been a WEEK now, and the car is still strong, with no SES. Enlighten me!
Okay, this post will be long, but please bear with me. First off, a little bit of history. All the bolt-ons in my sig were installed a few months ago. After the cutout in my exhaust, the factory Z28 dual setup is still mounted. When I got my tune done with HP Tuners, it was decided that we tune with the cutout closed; afterall, it WOULD be annoying as hell to go through the lengthy process of tuning while making all that damned racket.
So, the tune was done, and goodness gracious the Z sure did scream! We drove around for a half-hour to monitor the long-term values in the PCM. All was well, and so the tuner headed back home. Well, me, being the V8 sound-lover that I am, open the cutout and have driven it that way ever since. The SES light came on the day after the tune. I got the codes pulled, and they were P0172 and P0175 (Banks 1 and 2 System Rich).
Well, after discussion with my tuner and countless numbers of other LS1 folks, it was concluded that my 02 sensors suck, being the product of an LS1 with 94,xxx miles. BUT...In the time between the tune and now, I had rendevouzed with my tuner yet again so he could try tweaking some more, just in case the codes were a tuning issue. I closed the cutout, and we began the tune. Tune done, long term values evaluated, everything fine, car screams again, tuner goes home. So, yes, you guessed it, I open the cutout again. The same exact thing happens. SES comes back on the next day.
I got the codes pulled again, same issue, system rich. This time, a new person at AutoZone pulled the codes, and her first response was "Uh oh, time for new oxygen sensors!" Now, after hearing that same O2 theory over and over, coupled with AutoZone Girl's initial response, I must admit to having a reassuring sense that my problem could be solved by one simple purchase of new O2 sensors.
Now, besides the stupid SES light, I must go into detail about the performance-hindering symptoms. Vaguely described, with SES on, under WOT the car simply wouldn't respond like it did right after the tune. Moreso, in 5th gear at specifically 70ish MPH, you could floor it, and nothing would happen. The car would sorta have a "shuddering" event in which, as long as I had the throttle mashed to the floor, it would seem as though the PCM was pulling timing, or perhaps severely leaning the A/F mixture. It simply wouldn't accelerate. Also, it seemed to do the same thing, though less exaggerated, at high RPM in other gears. I know what you're thinking..."dirty MAF." Keep reading.
Now to the strangest part: For the past few weeks, I have been thinking about my situation, mostly while under the influence of mankind's best friend, beer. I thought about how, seemingly coincodentally, my car screamed like a banshee with a closed cutout after PCM flashes, yet upon opening the cutout afterwards in both instances, it was the same old story. So, last week, I closed the cutout. Immediately I'm disgusted by the factory sound, courtesy of the bathtub-sized factory muffler. Regardless, I head to Wal-Mart for some groceries, and would you believe, the goddamn SES goes off. I'm totally perplexed, because the theory of the cutout being the problem was disspelled by everyone I know, including LS1techers who responded to my numerous threads concering P0172 and P0175.
I do my shopping in Wal-Mart, with the car situation in the back of my mind the entire time. I get back in the car, crank her up, SES is still off. I start driving back to the bachelor pad, and LOW AND BEHOLD, all my power has been restored. No more sluggishness at high RPM, no more restricted acceleration in every gear, and a just a general feeling of restored performance. Gentlemen, can anyone out there explain this to me!? How can this be? It's almost as if the PCM was treating the cutout as one huge exhaust leak, triggering those system rich codes!? It has been a WEEK now, and the car is still strong, with no SES. Enlighten me!
Last edited by 1FST-Z; 05-08-2008 at 01:42 AM. Reason: Reader-friendlieness.
05-08-2008, 07:49 AM
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cutouts do affect tune i think. I have a minor tune. One night a bunch of us were messing around on an open road. I raced some others and there was a guy behind me who saw a flame coming from my cutout when i dropped it into 2nd.
So cutouts do make the tune a little rich, just tune the car for the cutout open.
So cutouts do make the tune a little rich, just tune the car for the cutout open.
05-08-2008, 12:31 PM
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fortmyers:
Do you think the whole problem can be avoided by just going with an aftermarket catback? You know, still have the sound/performance but no tune problems...
Do you think the whole problem can be avoided by just going with an aftermarket catback? You know, still have the sound/performance but no tune problems...
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05-08-2008, 03:19 PM
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Well i'm sure I can pick up a used catback for a fraction of that cost. Point being, I'm willing to do what I have to in order to get my car running right. So to further the discussion on this topic, what are we talking about here, a backpressure issue? Something to do with the cutout being too "free-flowing" ?
05-08-2008, 04:20 PM
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Well i'm sure I can pick up a used catback for a fraction of that cost. Point being, I'm willing to do what I have to in order to get my car running right. So to further the discussion on this topic, what are we talking about here, a backpressure issue? Something to do with the cutout being too "free-flowing" ?
05-08-2008, 05:03 PM
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Lickeyman:
Well that's the weird thing. The cutout is mounted in the spot that everyone apparently mounts theirs, near the rear axle, passenger side, roughly right behind the passenger seat. I wonder if perhaps I have an exhaust leak up at the header/y-pipe join, you know, like to where the cutout exaggerated the leak and triggered the O2s...
Well that's the weird thing. The cutout is mounted in the spot that everyone apparently mounts theirs, near the rear axle, passenger side, roughly right behind the passenger seat. I wonder if perhaps I have an exhaust leak up at the header/y-pipe join, you know, like to where the cutout exaggerated the leak and triggered the O2s...
05-08-2008, 05:18 PM
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Lickeyman:
Well that's the weird thing. The cutout is mounted in the spot that everyone apparently mounts theirs, near the rear axle, passenger side, roughly right behind the passenger seat. I wonder if perhaps I have an exhaust leak up at the header/y-pipe join, you know, like to where the cutout exaggerated the leak and triggered the O2s...
Well that's the weird thing. The cutout is mounted in the spot that everyone apparently mounts theirs, near the rear axle, passenger side, roughly right behind the passenger seat. I wonder if perhaps I have an exhaust leak up at the header/y-pipe join, you know, like to where the cutout exaggerated the leak and triggered the O2s...
05-08-2008, 05:21 PM
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Yep, I'm gonna pick up 01ssredA4's Hooker system, eventually pick up some C5 rears to play it safe, get rid of the cutout and call it done. I figure the tradeoff of ditching the cutout for what is still a great sound and great performance is well worth it in the end.
05-09-2008, 11:38 AM
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cutouts can effect the o2's. they do on mine. fresh air can find its way back up in there if the cutouts are too close to the sensors. tune it right with them closed then put it in open loop, or move the cutouts further downstream.
