Help! Full throttle bogging out

If anyone could help, or have any insight it would be much appreciated.
My 99' GTP will start & drive normal all the time but when i accellerate hard (1/2 throttle to the floor) the car will bog out, boost gauge will fluctuate, rpm's will flutter and it will have a very hard time accellerating. But once i go back to 1/2 throttle or less, it will take off & be fine. Is this a restriction by the computer or is this something wrong?

If anyone could help, or have any insight it would be much appreciated.
My 99' GTP will start & drive normal all the time but when i accellerate hard (1/2 throttle to the floor) the car will bog out, boost gauge will fluctuate, rpm's will flutter and it will have a very hard time accellerating. But once i go back to 1/2 throttle or less, it will take off & be fine. Is this a restriction by the computer or is this something wrong?

How many miles on your GTP? Based on your description you've got a problem.

77,000 miles, no check engine light.

77,000 miles, no check engine light.

Any mods? Did you fix or replace anything before this started? Anything else beside what you wrote about? Temp up? Last time tuned, air filter, gas filter changed?
ANYTHING?

Sounds like a bad catalytic converter, my car did the same thing. Most shops can check that for free. Plus Pontiac will probably fix that for free anyway cause it should still be under warranty. Good luck.

Sounds like a bad catalytic converter, my car did the same thing. Most shops can check that for free. Plus Pontiac will probably fix that for free anyway cause it should still be under warranty. Good luck.

Good point. It could be the CAT convertor and he needs to move fast since there's 77K miles on the car. The GM powertrain control /emissions warranty is 80,000 miles/8 years - whichever comes first on the CAT.

Doesn't hurt to rule it out.

No modifications so far except for a k&n and an adjusted wastegate(pushing it down) other than that, so far i replaced the exhaust, fuel pump, fuel pump ballast resistor,transmission,rack & pinion,fuel filter.and it still does it. If the cars cold, or just started up and i tromp on it, its fine- but after it warms up and i tromp on it, then it hesitates.

No modifications so far except for a k&n and an adjusted wastegate(pushing it down) other than that, so far i replaced the exhaust, fuel pump, fuel pump ballast resistor,transmission,rack & pinion,fuel filter.and it still does it. If the cars cold, or just started up and i tromp on it, its fine- but after it warms up and i tromp on it, then it hesitates.


Hopefully we can help you narrow it down now that we know what you've got on it. Are you using that K&N filter spray on your K&N air filter? If so, try cleaning the MAF sensor. It may have contaminated the sensor air flow hot wires. Try cleaning the complete throttle body. For troubleshooting purposes you can disconnect the MAF and it should run to test it. Otherwise you could be looking at ignition such as spark plugs, wires, ICM or coil packs or possibly fuel injection. Can you correlate a certain RPM where this problem occurs?

Well, the car has been doing this since i bought it at 53,000 mi, i just put the k&n in it so i didnt spray it yet, shortly after i bought the car i sprayed cleaner in the throttle body just for p/m purposes. As for correlation between the problem and the engine revolutions-they are not related, wether the car is at 2000 rpm or 5800 rpm- as soon as i floor it it hesitates until i go back to 1/2 throttle, then its fine. I havent done any tune up yet and i know i should, but wouldnt a problem like that be multiplied when in wet or damp weather? Or do it all the time?

Also i dont know if its related or anything but when i went to go get the filter (air) i threw out the old one, then drove to go get one. Got it. then drove back home & installed it. Through the whole way of not having an air filter, it ran beautiful. But as soon as the k&n went in, it bogged down.

Well, the car has been doing this since i bought it at 53,000 mi, i just put the k&n in it so i didnt spray it yet, shortly after i bought the car i sprayed cleaner in the throttle body just for p/m purposes. As for correlation between the problem and the engine revolutions-they are not related, wether the car is at 2000 rpm or 5800 rpm- as soon as i floor it it hesitates until i go back to 1/2 throttle, then its fine. I havent done any tune up yet and i know i should, but wouldnt a problem like that be multiplied when in wet or damp weather? Or do it all the time?


In your case you might want to start with the basics such as spark plugs and wires first. Those items are critical on a Series II 3800 with or without supercharger with 53K miles. If that doesn't work try disconnecting the MAF sensor. It doesn't cost you anything and doesn't hurt to rule it out. You can safely run the car with it disconnected for a short period of time. Do you know where the MAF sensor is located on a Series II 3800 SC? Once you find it and disconnect take it out for a spin and see what happens.

After that start looking at high voltage ignition. Another thing you can do is ohm out the fuel injectors with a multimeter and make sure they are in spec resistance wise.

Other than that don't know what other advice to give you. I'm sure others will weigh in.

Also i dont know if its related or anything but when i went to go get the filter (air) i threw out the old one, then drove to go get one. Got it. then drove back home & installed it. Through the whole way of not having an air filter, it ran beautiful. But as soon as the k&n went in, it bogged down.

The air filter should not cause the bogging unless it is defective which I doubt and you appeared to have the problem before hand. BTW - Also check the IAT (Intake Air Temp) sensor and make sure it is connected properly. It is located on the rubber intake before the throttle body and air cleaner assembly.

You might want to try the MAF sensor (Mass Airflow) test I mentioned earlier. Good luck!

Just a thought but something large (like a leaf) or something could have flown up into the intake as you drove home without a filter and it could have happened just before you pulled into the driveway so you didn't notice it. Anyway it's worth checking.

I have agree with 92bonny. I had the exact same problem with the bogging down on heavy acceleration, it was the CAT. Once replaced my GP had all kinds of power and the tranny shifts great into downshift on heavy acceleration. The first time out I lit up the tires where before I had hardly any power. I also had 2 of the 3 coil packs shorting out, but the shifting was cured with the new CAT. Good Luck.

We,ll guys. I took it into the dealer today to see for sure what it was and low & behold it was the cat. So the cars gonna sit there for a few days while they get it in stock & install it. Thank you
so much for your imput, and hope to line up next to ya sometime in the future.

I cant believe this!!!!! I get the car back after they put the new cat in and its fine. Not 4 days later the problem comes back! I doubt the cat is clogged again its impossible!But its weird because its the same EXACT priblem which was earlier rectified by the new converter. HELP???????

how much the same? literally exactly (same 1/2 throttle bogging etc)? If not state what differences. My Z28 did that too after being in the shop, as soon as I can remember what the next problem was I will post.

YES. Exactly the same. In all circumstances listed before.

I cant believe this!!!!! I get the car back after they put the new cat in and its fine. Not 4 days later the problem comes back! I doubt the cat is clogged again its impossible!But its weird because its the same EXACT priblem which was earlier rectified by the new converter. HELP???????

Bummer! Guess its back to the drawing board. Well, I've already thrown in my 2 cents. Good luck!

http://www.photodump.com/direct/coolrex/gtp558.jpg
Thrasher CAI, DHP v1.0 ECU, Granatelli CAI Tuneable MAF,
3.4 SC pulley, Hi-Flow CAT, u-bend delete, 180 TS, TB spacer
ET: 14.3 @ 96 mph

It was the fuel pump, it acted similarly to a bad cat, I would check that out as your next step, I am almost certain that's what it is. Good Luck.

It was the fuel pump, it acted similarly to a bad cat, I would check that out as your next step, I am almost certain that's what it is. Good Luck.


If you read one of his prior messages in the thread, he claims the fuel pump has been changed. :dunno:



http://www.photodump.com/direct/coolrex/gtp558.jpg
Thrasher CAI, DHP v1.0 ECU, Granatelli CAI Tuneable MAF,
3.4 SC pulley, Hi-Flow CAT, u-bend delete, 180 TS, TB spacer,
MSD 8.5mm wires, AC Delco 41-932 spark plugs
ET: 14.3 @ 96 mph

It was the fuel pump, it acted similarly to a bad cat, I would check that out as your next step, I am almost certain that's what it is. Good Luck.
- sorry
I can post this on another forum if you like and see if they can come up with anything. In the meantime, by a small margin, you might have ended up with a defective cat, have it checked again to be sure, can't hurt.