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straight pipe kill mpg??? no 02 sensor.

J

jgoodhbc1

New member
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
 


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??
 
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
 


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.
 
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?
 
jgoodhbc1 said:
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?
Click to expand...

Keeping up with a GTP + Low MPG = cam? Something doesn't make sense as who cams a lesabre?
 


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...
 


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.
 
jgoodhbc1 said:
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.
Click to expand...

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 :)
 
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?
 
Use your '98 PCM.

Use the throttle body off the motor you took out.

A new rubber gasket is like 3 bucks.
 
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