Thread: Unresponsive 3.8 Liter Acceleration and Strange Sound at 4500RPM

I have a 2002 Pontiac Grand Prix GT 2 door with a 3.8 liter v6 and 93,000
miles. 2 wheel bearings, 2 tires, tune-up, and transmission fluid change
was done, and I keep having the same issue. Basically under slow
acceleration, the transmission shifts and performs without issue. Under
moderate to full acceleration, like when getting onto the highway, the
car won't shift, and will hold itself in gear at 4500 and the engine just
continues to make raise loudly until I let off the accelerator slightly, and
it shifts. I used to only notice the issue under full acceleration, but now
the issue is becoming more noticeable under moderate conditions, such as
merging onto a freeway, which is becoming slightly dangerous.

My mother drove the car, and she said the experience was similar to a
1.6 liter Hyundai Accent she drove, which felt powerless and difficult to
drive on the highway. Today when I was merging onto a bypass, I floored
the car at about 30 mph and the engine made a loud grating, sound,
similar to putting cards in the spokes of a bicycle. I heard the same sound
when the engine blew in a 3.4 liter v6 Grand am. I let off the gas and
pulled over and the engine was running quietly, and the temperature of
the engine appeared normal. The engine starts and runs very smoothly,
and the spark plugs and wires, as well as the air filter had been replaced
recently during the tune-up. At one point when I was travelling at 50 mph
I floored the gas and watched the car take approximately 20 seconds to
accelerate to travel to 70mph.

We once had a Chevy Venture Minivan with the same engine and at about
134,000 miles, the trans started going and it had trouble shifting on the
highway. I'm wondering if this is possibly the same issue, and the trans is
on its last lap at 93,000 miles. I'd appreciate some of your input, thanks.

Guys thanks for your input. I was wondering if anyone had any "guesstimates" in
regards to what I could be looking at. I've already put a bit into the car in small
maintainence issues, thanks.

If you do have a clogged cat., this is an indication that somthiong on the engine is not working properly. A cat converter should theoreticly last the entire life of the car, unless the a/f ratio is such that is causes the cat to over heat and lmelt down, or get glogged some otherway. Point is, they dont just go bad, but the sysmptoms you described does sound like a clogged/melted/broken cat. converter.

I'm not extremely mechanically inclined, but I don't mind getting my hands dirty for
DIY kinds of repairs. I was wondering if I bought a new cat, would I be able to unbolt
it from the bottom of the car, and replace it, or is there flamework/cutting/soldering
involved? Thanks

I would also say clogged cat. My car is also a 02 gt and had very similar problems. Once I replaced the cat, all problems went away and the car ran like new.
MY suggestion to you is to buy this MagnaFlow 23405 - Direct Fit Catalytic Converter | O'Reilly Auto Parts

I believe advanced auto sells them too, not positive though.
Not only are you replacing the bad cat but your replacing it with a higher flowing cat, AND deleting the U-bend (the most restrictive part of the exhaust on these cars). All for about 200 bucks. No welding involved simply soak the sh*t outta the old exhaust bolts with PB blaster and remove the bolts and replace with new cat.

PS. The cat's on these cars are so notorious for going bad GM actually recalled the cat's on them. Mine was within the VIN range but was over 120k miles or 10years, whichever comes first. Mine took a crap at 126k (go figure). Personally though, instead of trying to d*ck around with the dealership, go the magnaflow route. Your car will sound a little better, run ALOT better and even get a few ponies outta it.

Hope this helps.....