Engine bogs on takeoff

[mtup]

My daughter has a 2002 grand prix se with a 3.1 engine. This car really bogs and jerks during take off so i changed the fuel filter, air filter, spark plugs, plug wires, cleaned the MAF sensor with MAF sensor cleaner and cleaned the throttle body. I have an OBD II Auto Scanner I bought from Autozone a few years ago. It was the best one they had out of the two they offered and it says everything has passed. No Codes! Also the car ran hot on her and warped one of the heads so i had them milled and a valve job done. They checked for cracks and all. This engine runs really good, starts exellant, idles beautifully and i can hold the gas down at 2000 or 3000 rpm while in park and the engine doesn't do this. Once you get to about 50 mph it runs fine. Smooth as glass. Any help surely would be appreciated. If anyone wants to know where something is on this engine just let me know.......lol

[Stealthee]

Check the trans fluid.

[mtup]

Actually I did that right away. It was a pint low. It's full now. The engine sounds as if you kicked in your four barrel without an air filter on it.

[olopezm]

I would say it sounds like a catalytic converter problem to me, you hould be able to diagnose a plugged cat with a vacuum reader gauge tester.

Take a look at the following link, even when your car is a 3.1 you might want to check with a dealer; I hope it helps.

http://www.automotiveforums.com/vbul...d.php?t=681283

Oscar.

[tblake]

Can you get it to happen when you powerbrake it in drive?

[mtup]

Now that I have gotten her overheating problem fixed and had time to drive it more I find that it is the transmission slipping. Yes I did power brake and they were hard like I lost the vacuum booster or something. I added even another pint in the transaxle and it still shows full but is doing better as long as she takes it easy. Next weekend I will change the fluid and filter in the transmission. One guy at work did that to the exact same car and 50,000 miles later it's still fine.

Thanks all

[FISH96]

is power braking an orthodox and accepted method of troubleshooting? does it not place undo stress on the transmission not to mention other systems? is this sound advice?

[mtup]

Well, it's not the transmission although it was slipping a little. The car still bogs on takeoff but does fine after you get going. I tried it in reverse and the same thing occurs. The only thing I haven't done yet is get the fuel pressure checked. I figured it takes the gas fine after it gets going and you let off a split second. Still no codes except and occational EGR. Anymore suggestions? Will let you know fuel pressures when I get them. Thanks all

[olopezm]

I know this sounds like "crazy diagnosing" but how about you start disconnecting each sensor (MAP, MAF, TPS, IAT, ECT) one at a time and see if any makes a difference during a short test drive.

Oscar.

[mtup]

Ok the fuel pressure is ok. Turning the key on gives me 58 psi. After starting the engine it drops to 49 psi. I don't know where to turn next. Anyone with any idea's?

[Tech II]

Let's get back to the cat.....

With vehicle at normal operating temp, from a dead start, lay into it......does it bog down and refuse to upshift?

If yes, come to a stop.....now feather the gas pedal and accelerate gently......does it shift and slowly get up to speed?

If yes, then my guess would be a catalytic converter problem.....

[mtup]

I just took the car out and tried what you said Tech II. It does refuse to upshift when getting down on it. It will stay in a low gear until I let off the gas. Feathering it made it cut out. I can gas it a little and when it bogs let up a bit it will shift. Sitting in park I can get it up to 3000 rpms holding and it is smooth. after that it starts cutting out. Sounds like the cat huh? There has never been a rotten egg smell if that helps at all.

[mtup]

Thanks Tech. We changed the cat and the car runs great.

[Tech II]

Olopezm hit the nail on on head first......