Thread: straight pipe kill mpg??? no 02 sensor.

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  1. #1 straight pipe kill mpg??? no 02 sensor. 
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    Recently I have replaced the motor in my 98 grandprix gt. I replaced it with a 99' buick lesabre 3.8. When the former blow blew( intake gaskets go figure) it plugged the cat... So i cut it out and just straight piped it... I have heard about the 02 retarder from zzp performance... But currently I am averaging barely 20 mpg on the highway! Is the rear 02 sensor being causing this??? What are your thoughts
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  2. #2 Re: straight pipe kill mpg??? no 02 sensor. 
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    Also.. I noticed online the buick motor i have in my car was rated at 10 more hp.. is it injectors? computer? I have the computer from the buick still.. Would they interchange??
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  3. #3 Re: straight pipe kill mpg??? no 02 sensor. 
    The Blue One blueguy's Avatar
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    Because you need your '98 PCM.
    Sold WBody's: '03 Blue GTP/'98 Green GTP/'98 Silver GT/'05 GXP
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  4. #4 Re: straight pipe kill mpg??? no 02 sensor. 
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    different maf's guy.

    swap your old TB onto the new engine.
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  5. #5 Re: straight pipe kill mpg??? no 02 sensor. 
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    I am not entirely sure on this so maybe someone else with a little more knowledge can help me out here but I believe if you cut out the cat and straight pipe it you would need to get a tune just like if you were to put in a hi-flow cat. Like I said I am not positive on it so don't take my word just yet
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    I live here. MoarkatsINmuhtrailer's Avatar
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    He's not 01+..it don't matter too much. All he could do is just have the computer set to not report the codes
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  7. #7 Re: straight pipe kill mpg??? no 02 sensor. 
    Turbo is the way to go. BillBoost37's Avatar
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    As mentioned, the difference in the maf table may be doing it. I'd also put a fresh front O2 in. Those are the two most likely causes.

    Your 98 doesn't run any cat tests like the 01+ cars and dump fuel if the rear sensor is missing. Therefore..front 02 and Maf are the only items that should be causing you an issue.
    I drink..so consider that when reading my posts.

    2010 Audi A6 Dual IC's
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  8. #8 Re: straight pipe kill mpg??? no 02 sensor. 
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    Sweet thanks. I raced a friends gtp and I stayed right with him most of the way. So extra power is nice.. But the mpg's are going down the tube and I drive 60+ miles round trip everday for work. Thanks for the input. So Billboost37... Is the throttle body bigger on the buick motors? And not same maf's?
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  9. #9 Re: straight pipe kill mpg??? no 02 sensor. 
    GXP Level Member Tuner-Extraordinaire's Avatar
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    my mpgs got better catless.

    full on straight pipe w/no muffler WILL reduce highway mpg though.
    Whine with your Cheese?
    Stock+Self Tuned. Going for low 14's everyday.
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  10. #10 Re: straight pipe kill mpg??? no 02 sensor. 
    GTX Level Member EJOUIE's Avatar
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    Quote Originally Posted by jgoodhbc1 View Post
    Sweet thanks. I raced a friends gtp and I stayed right with him most of the way. So extra power is nice.. But the mpg's are going down the tube and I drive 60+ miles round trip everday for work. Thanks for the input. So Billboost37... Is the throttle body bigger on the buick motors? And not same maf's?
    Keeping up with a GTP + Low MPG = cam? Something doesn't make sense as who cams a lesabre?
    97 GT white 4 door-SOLD

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  11. #11 Re: straight pipe kill mpg??? no 02 sensor. 
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    Quote Originally Posted by EJOUIE View Post
    Keeping up with a GTP + Low MPG = cam? Something doesn't make sense as who cams a lesabre?
    GTP probably had 87oct and a plugged cat for a GT/l36 to keep up
    Whine with your Cheese?
    Stock+Self Tuned. Going for low 14's everyday.
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  12. #12 Re: straight pipe kill mpg??? no 02 sensor. 
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    no 87oct.. He doesn't want pingin/detonation. It is a tired gtp though.
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  13. #13 Re: straight pipe kill mpg??? no 02 sensor. 
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    Quote Originally Posted by jgoodhbc1 View Post
    no 87oct.. He doesn't want pingin/detonation. It is a tired gtp though.
    bad bov then.
    Whine with your Cheese?
    Stock+Self Tuned. Going for low 14's everyday.
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  14. #14 Re: straight pipe kill mpg??? no 02 sensor. 
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    No cam.. again it is a TIRED gtp 2dr.. that I raced and mine is not. body has 177k on it but motor is just over 100k. He's pushing 250k+ stock motor no work done. lol...
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  15. #15 Re: straight pipe kill mpg??? no 02 sensor. 
    The Blue One blueguy's Avatar
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    happened in this thread.

    Swap the TB already.

    And run your factory PCM.
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  16. #16 Re: straight pipe kill mpg??? no 02 sensor. 
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    Quote Originally Posted by jgoodhbc1 View Post
    No cam.. again it is a TIRED gtp 2dr.. that I raced and mine is not. body has 177k on it but motor is just over 100k. He's pushing 250k+ stock motor no work done. lol...
    miles have no bearing if the motor is on the up and up. likely a bad bov or severe loss of compression.
    Whine with your Cheese?
    Stock+Self Tuned. Going for low 14's everyday.
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  17. #17 Re: straight pipe kill mpg??? no 02 sensor. 
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    Thanks for the help. Will do. I was just curious as to why the throttle body is making that much difference. And PCM still stock. Thanks again.
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  18. #18 Re: straight pipe kill mpg??? no 02 sensor. 
    The Blue One blueguy's Avatar
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    Quote Originally Posted by jgoodhbc1 View Post
    Thanks for the help. Will do. I was just curious as to why the throttle body is making that much difference. And PCM still stock. Thanks again.
    Because the '99+ cars had a different throttle body.

    With you having a '98 PCM or '98 TB with a '99+ PCM or '99+ TB...it's skewing the MAF tables...and running super lean.

    yay, fix it
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  19. #19 Re: straight pipe kill mpg??? no 02 sensor. 
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    Ok. so last question and i'll get it fixed. I will have to buy a 98 throttle body and started new job from a layoff. so money is tight right now... but i have the 99' pcm.. which is better? switch tb or pcm?
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  20. #20 Re: straight pipe kill mpg??? no 02 sensor. 
    The Blue One blueguy's Avatar
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    Use your '98 PCM.

    Use the throttle body off the motor you took out.

    A new rubber gasket is like 3 bucks.
    Sold WBody's: '03 Blue GTP/'98 Green GTP/'98 Silver GT/'05 GXP
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