Power not transferring from engine to wheels

[merowe]

Hi all,

Recently, I started experiencing a problem with my 2002 Pontiac Grand Prix (78,000 miles). Around 2 weeks ago, I gunned the car on the free way and the gear dropped properly (with proper RPM increase), but the car didn't speed up. Instead, it felt like the car was coasting.

Presently, the problem seems to be getting worse (I don't drive the car too much). The same thing as above happens, but I don't have to gun it hard anymore. I feel that, at high speeds (45+), when I push the gas pedal down enough to where the transmission should go down a gear to accelerate, I start coasting instead. This is not always true just yet, though.. Sometimes it does work.. However, it never works if I try gunning the car anymore. I'll just end up coasting with the engine properly working hard.

It seems to me that the power is getting lost somewhere in the process (transmission?). I don't hear any unusual noises either (grinding, etc..). Driving on side roads at slower speeds (25), it seems everything is fine. Oh, and if I get the car up to 75, the car feels jerky (slows down, speeds up, slows down, etc.. each for a split second).

Any ideas on what may be going on? I need to see if any codes show up, but I do not get a service engine light popping up or anything. Anyone have any ideas? Thanks!

[tblake]

You need to take it in and have it scanned for codes. A trans capable scanner will be needed. Either take it to a tranny shop or to a dealership. At a tranny shop you can also get a quote of a rebuild because I'm pretty sure you have a slipping clutch or band in your trans.

[grandprixgtx00]

as stated above...get the car scanned for any codes, you may also want to get the torque converter checked.

[BNaylor]

Hard to tell by the OP's description of the problem but does the coasting occur only after it has shifted to 4th - OD and torque converter clutch (TCC) lockup? It would seem so since it acts up at speeds of 75 mph and above 45 mph. What happens if you keep it in manual shift only? Don't put the gearshift selector in 4th - OD and keep it no higher than D3 for testing. Let us know what you get.

If this problem only occurs in 4th gear (OD) then the 4th clutch shaft is probably bad. The splines at the end of the shaft strip because the shaft is not good quality hardened material and wears out after sufficient mileage accumulation. A coasting feel or the car feeling like it is in neutral is one symptom. No DTCs will set.