Power Loss When Acceleration

[Prix87]

Hey Guys,
Driving a 97 Grand Prix GT, 130k miles...
Recently I've had my SES light come on due to a bum Oxygen sensor. Had the head pipe/cat replaced with a new 02 sensor. Anyways, around that time I was having acceleration problems when i really layed on the throttle, or up-hill if the car had to shift gears. It doesn't always do it under the same conditions. It's hard to explain exactly what it's doing but it's kinda like a repetitive jerking until the car shifts to the next gear. Don't get me wrong, the car drives terrific under normal driving conditions. In fact you'd never know there's a problem if you didn't step on it. But knowing it's there, there's obviously something wrong. I've been told by a buddy that it could be an EGR valve, but i'm not sure
I, myself doing regular maintainance have replaced the air intake temp sensor, PCV valve/MAP sensor, again 02 sensor, ignition coils-plugs-wires, evap solonoid and purge valve.. aside from regular coolant,oil and tranny fluid checks its a very clean car under the hood.
... Any advice would be greatly appreciated -Thanks

[no more pontiacs]

I just went through the same thing in my 2002 pontiac grand prix (latest issue) anyway it was a clogged catalytic converter. $560.00 repair bill at gm authorized dealership.

[richtazz]

Any check engine light and if so, what codes? Also, when you changed the PCV valve, did you remember to remove the black o-ring from the old one and transfer it to the new one. If not, your jerking could be caused by a vacuum leak at the PCV valve, causing the MAP sensor to get inadequate vacuum and "confusing" the PCM.

[GPFred]

I had dealt with a similar issue involving low voltage to the O2 sensor and poor acceleration. After many expenditures for other issues as well, the fuel filter seemed to be the primary cause of the exceleration issue. Could try that as it is fairly inexpensive.

[Prix87]

I just replaced the fuel filter about 10 months ago. I've been reading some of the other threads and i'm almost wondering if it's a sensor in the transmission or something. As the car accelerated it's a couple of jerk/jerk/jerks before its to the next gear. Sometimes they're barely noticable, other times it's a bit more vigerous

[richtazz]

Did you check for the o-ring on the PCV valve I mentioned above????

What brand plugs and wires did you install? GM 3800's do not like Bosch plugs at all and run like doggy-doo on them.

[Prix87]

The thing is that i had changed plugs/wires months ago and has run fine up untill a couple of weeks ago. ran great actually with them. wasn't until I had problems with o2 sensor signaling ses light. also had a bum coil causing the 3 cylinder not to fire poor idle. I swapped the coil the very same day that problem occured. but the jerk/jerk/jerk was around before the coil but after the o2 sensor problem. I will however recheck pcv valve for that gasket...

[richtazz]

Your 97 was the last year that they used the 4t60e transaxle in these cars. That trans has a vacuum modulator that controls shifts. If the previously mentioned PCV o-ring is missing, that could be the root of the jerking problem also, as the trans isn't getting a proper vacuum signal.

[Prix87]

A vacuum modulator ehh? Is that a DIY or am I taking this baby in somewhere?

[richtazz]

The vacuum modulator is a very simple change. It is located on the transaxle case, on the front side between the engine block and the trans side cover. It has one vacuum line running to it, and a single bolt retaining a forked bracket that holds it in the trans.

[Prix87]

success!
Just got the new modulator in the mail today and swapped the old one out. As soon as i turned the old one upside down tranny fluid came pourin out. Haynes manual says if thats the case its shot. Took her out for a spin and no jerkn or hesitation at all.
Thank you so much Richtazz, Of all the people I've talked to, none of em' mention a bum modulator
-thanks again