2002 Pontiac Grand Prix GT Awkward Shifting Behavior

[HWYSPEEDER]

I've always been a fan of the 2 door Grand Prixs (can't afford the GXP or
6.0 GTO yet) and about 2 months ago I found a 2002 Grand Prix GT at a used
car dealer with 91,000 miles, with a very clean body/shiny paint, no
accidents on the carfax report. The engine ran quietly and the transmission
seemed to shift normally from the short test drive I took, and I kicked it
around in my head for a few days, looked at a couple other cars and went
ahead and bought it. The next day I took it to the Buick GMC dealership for
a tune up service, and they replaced the spark plugs, air filter, a strut,
some brake pads, and an oil change. After that I parked the car for about a
month and a half and really didn't get the chance to drive it because I was
swamped at work. About 2 weeks ago I took the car out for the weekend about
3 hours away, and I noticed when I floored the gas a couple times, the car
didn't upshift as responsively as my 08 Grand Prix. I just thought it was kind
of a quirk and didn't really think much of it. The next day when I was on an on-ramp
I floored it from about 30 mph, the engine raised to about 4500 rpm and held it
there for several seconds until I slightly pulled off the accelerator, and then
it changed gears and accelerated up to speed. At about 45 mph, whenever I would
gun it, it would literally redline before changing gears at a slow pace, when
generally I believe it's supposed to change gears at the yellow mark. When driven
conservatively in-town or getting on the highway, it shifts without any issues
apparent, but when you floor it to get up to speed, it either holds the gears or
shifts slowly.

I took it back to the dealership and they suggested I perform an automatic transmission
filter drain and fill. Afterwards, the mechanic drove the car and said he could not
replicate the issue, and the transmission was within specification. On my way back from
the dealership, I experienced the same issue when I floor it, which is problematic when
pulling onto the road and trying to get the car up to speed. My 08 Grand Prix has the same
3.8 liter V6, and when I floor it, it'll shift almost immediately and pull strongly up to
about 90 mph. I told the mechanic about the marked difference between the 2 cars, and he
said the engines are mechanically identical, but the transmissions on the older bodystyle
are different. I've never seen a basic auto transmission behave this way under acceleration,
unless it was some kind of BMW/Audi paddleshift transmission with a sport mode activated.
This car's transmission doesn't have anything like that. I know when the miles start getting
up there, auto GM trannys aren't the most reliable in the world, but even at 91k, I'd think
this would be a little early. When I drive it and floor it, it's a very akward experience of
modulating the gas in order to shift to get up to speed. I always liked the pull of the 3.8 V6
even though it's no corvette, but this is really taking the pleasure out of driving the car.
If someone could give me some advise on what the possible issue could be, I'd appreciate it, thanks.

 

[madden_02]

I had almost the exact problem last summer. When I would drive around town everything seamed just fine, would shift gears like normal. But when Ii went to get on interstate and I would floor it, it wouldn’t shift from 2 to 3. The rpm's would climb and if it keep it floored the check engine light would start flashing. As soon as I would let off the gas the littlest bit it would shift and the check engine would go back off. The problem on mine was a partially clogged catalytic converter. When ii would floor it the exhaust couldn’t escape fast enough and was causing back pressure on the motor which was causing the motor not to be able to get where it wanted to be to allow the car to shift. Total bill was 575 to get a new catalytic converter installed at a local shop.

Madden

 

[HWYSPEEDER]

I'll tell them to look at that, I actually felt it wasn't as quick as these cars are normally, I've driven a few of the old 3.8 impalas from work. This is definitely starting to turn into an immediate money pit lol.

 

[TLSheff]

Check the tranny fluid, if its not pretty red &/or if it smells kinda burnt, it needs to be changed. With those miles, unless it was abused like a red headed step child the tranny should be quite responsive, I know mine is

 

[Taz Magister]

hey if its the cat i got a stock down pipe with a good cat took it off around 65k miles you can have it for dirt cheap compared to the 575 who ever paid,

but yea change the fluid and throw in some type of additive or stop slip cause its probabally the clutch slipping

 

[UTfanatic80]

I kind of had a similar problem with mine, if you have changed the tranny oil then you may want to check all the vaccum lines. I had to replace the o-ring on the pcv valve and all was good after that. I don't believe it's the catalytic converter, in my experience with those if they become clogged your vehicle with go as slow as a turtle(zero acceleration).

 

[TLSheff]

I don't believe it's the catalytic converter, in my experience with those if they become clogged your vehicle with go as slow as a turtle(zero acceleration).

+ Spittin and sputtering at idle usually. Imagine if you will your v6 on2 cylinders, this is what it sounds and feels like