bad gas mileage

I need some help or suggestions. I have a 2000 Grand Prix 3.8 with 106k, just had the tranny rebuilt with Aamco. Got it back runs great, shifts smooth, but my gas mileage is horrible since it was fixed. Any help or ideas would be greatly appreciated. The only thing I noticed is my RPM's are running slightly higher since the rebuild. Thank

I had a friend take my car for a ride and he seems to think that my issue isn't with the new rebuilt tranny, but rather the torque converter not engaging or disengaging properly. He says that's why my rpm's are higher and my gas mileage is lower. Has anyone else out there having or had the same issue. Please let me know....Thanks

I need help. My 2000 Pontiac GP 3800 with 106k just had the tranny rebuilt and since I got it back, my gas mileage is horrible. The car runs and shifts great. The only different thing I noticed is the RPM's are slightly higher, and the car feels like it's dragging a little. Pls let me know if you have any ideas...:banghead:

It would be helpful to post what model Grand Prix you have since the final drive gearing ratio is different between models.

Thanks, It's 2000 Grand Prix SE 3.8 with 106k

If one like a 2000 model has the computer reset, would "re-learning" restore things like shift patterns and fuel milage?

Is there anything that I can do?? Will this issue resolve itself?? Thanks

I'm curious as to what your gas mileage is. Then we can compare to everyone elses gas mileage....

correct me if im wrong......but doesnt the 2000 Pontiac Grand Prix SE only come in a 3.1 V6, not a 3.8?? Cause i have a 2001 Grand Prix SE with the single exahust pipe and the 3.1 V6.

my mileage before the tranny re-build was around 23 mpg for mixed in town/highway. Now I'm only getting 15 mpg . What can I do or should I do to bring me back up to 23?

the 3.1 is standard, optional is 3.8, mine is 3800 series II

mabey when they were fooling around in your Engine, something came lose? air ratio is off?? Plugs messed up?? ask the guys at the shop what they did and exaclty what they fooled with on your Car

Thanks, I'll do that ... there has to be some explaination.

This is normal due to the tightness of the new transmission. Give if some miles and see if it improves. I have had two transmissions redone and have had the same results as you are having. The fuel mileage will improve as the transmission breaks in.

:rolleyes:

brookfjk,

Just how many threads do you plan on posting concerning the same issue? Please one thread at a time to cut down on confusion and redundant answers.

http://www.automotiveforums.com/vbulletin/showthread.php?t=693633

http://www.automotiveforums.com/vbulletin/showthread.php?t=693717

Thank you for your cooperation.

Edit Update: Threads merged together.


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If your RPMs are higher something is not right. Take it back to the shop if your RPMs are just a little higher its probably the TC not locking up. With a scanner they can tell you. Try pulling up on the brake pedel with your foot while driving at a steady speed above 50 and see if it locks up.

it sounds to me like your overdrive is not engaging properly, and you need to take it back to aamco and have them fully fix your transmission. Overdrive lowers your RPMs at crusing speeds and greatly increases gas milage, your GP has overdrive, and if it blew with your tranny and they neglected to fix it, that would explain your bad gas milage...good luck convincing AAMCO it's theyre fault

try increacing your timming to see if that is the problom