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Discussion Starter · #1 ·
I've recently installed a completely new exhaust on my 2005 V6 (Pypes Mid-Muffler and Pacesetter long-tube headers) and I've noticed from the beginning that there is a drastic loss of power. Entering the highway, I've noticed that once up to the power band the car does not make noticeable power beyond it. As if it's locking itself to the same output. I've talked on the phone to a couple tune shops near me, most of them seem confident that my problem is my A/F ratio, but all the shops are throwing ridiculous numbers. My question is why is my car making less power after the new exhaust install?



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It shouldn't.......DC the battery for 30 minutes, this will reset the ecm and it will start the learning curve again.......while there may be some shift of the power band, you're only talking a few hundred rpm....I'm betting one of the o2 sensors is either bad or the wiring was crunched during the install or...the ecm is still learning the A/F mix....
 

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Discussion Starter · #3 ·
2 Of the oxygen sensors had to be removed, and that's what the check engine light im getting is for (I used the code reader at auto-zone) and I have tried the battery disconnect. It didn't effect anything but the idle when start up.
 

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My guess would be that the PaceSetters need a dyno tune. While most headers don't require tuning other than disabling rear O2s if carless, I've seen some lower-end sets (PaceSetter included) needing recalibration to achieve the proper A/F ratio.
 

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Removing the rear O2 sensors is one of those things that you MUST tune for, isn't it?

The computer is looking for the signal from the rear O2's, but isn't getting it, so it is choking.

Just to test it, try a full throttle run. I am not an expert on this, but as I understand it, that puts the computer into "open loop" mode where it ignores the rear O2's, and maybe then it will run right.
 

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Removing the rear O2 sensors is one of those things that you MUST tune for, isn't it?

The computer is looking for the signal from the rear O2's, but isn't getting it, so it is choking.

Just to test it, try a full throttle run. I am not an expert on this, but as I understand it, that puts the computer into "open loop" mode where it ignores the rear O2's, and maybe then it will run right.
From my understanding on most cars, the upstream O2 sensors are the only ones that partake in A/F calibrations. The downstream sensors are only there to check if the cats are functional.
 

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Discussion Starter · #7 ·
I have gone full throttle a couple tmes, not for an extended amount of time obviously, but so much power has been lost that i need to go full throttle sometimes to get up steep hills. (even in higher RPM's)
 

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Ahhhh...I see the light...IMHO, I would not have removed the rear O2 sensors...they are the final determining factor for the ECM in adjusting the A/F ratio.......the "custom" tune that is referred to basically is a "You got to be kidding me" fix......yes, it will get rid of the CEL but, to have that advanced of a ECM software system and basically set it back to where is operates like an OBD I, it's well, not my vote of the year for a "fix"...buy 2 bungs, get a drill 7 a torch and reinstall those rear O2 sensors!
 

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From personal experience, I installed an off road H pipe before I quite had the tuner in my possession. My car didn't run terrible but it didn't run quite right until I got the proper tune in it. Now it runs like a champ. I would look into either geting the O2 sensors properly installed again like the other guy said or look into getting the car tuned properly for your mods.
 

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Did you remove the catalytic converters? That may be why you're car is running badly. You definitely need a tune with the long tubes.
 
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