2000 Grand Prix GTP supercharger fluctuates when accelerating

The coupler is not the issue. You need to pull the whole unit and check the vanes.

Have some one tap it for you while you're under the hood to track it down and then disconnect at least one of the wires. You can also try looking at your fuse box or where ever your relays are and look for the horn or horn picture. Either of those should do the trick so whatever's easier.

P0306 PONTIAC - Cylinder 6 Misfire Detected https://www.autocodes.com/p0306_pontiac.html

P0141 PONTIAC - O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 2
P0141 Pontiac O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 2

The spark plugs have absolutely nothing at all whatsoever to do with boost levels.

However; change them anyway because new plugs are always better. In the GTP, don't use the iridium plugs, use copper core. I highly recommend Autolite 605's, gap them to .055"

In the GTP, spark knock is a common, performance robbing issue because of the supercharging. You'll lose 5-6 horsepower for every degree of timing ****** that the engine computer will employ to prevent the spark knock. If you use copper core plugs though, this problem will be less likely because copper dissipates the residual heat much faster than iridium, so that only the electrode spark alone can be hot enough to ignite the fuel. The only other difference between the plug types is how long they last. Iridium plugs were the originals only because they last longer...they offer no performance benefit to the GTP.

Now on to your actual question.

There only a few causes for loss of boost pressure in the GTP, all of which are an easy fix.

Supercharger belt slip, disconnected or damaged boost bypass valve hoses, or maladjusted boost bypass valve linkage.

The easiest thing to do first is the boost bypass valve adjustment. This will produce results even if you DO still have belt slip or a leaking hose.

Locate your boost bypass valve. You will find it mounted directly in front of where the throttle body bolts into the intake plenum.
You will see that it is held in place by three bolts. Loosen them in this order; left, right and rear. You will find that you'll need a 4" extension socket to reach the rear one. Hold your socket on that one while you push down on the valve body. As you may notice the mounting bolt holes are elliptical, allowing for the height adjustment. You can use this as a visual reference for how far to push the valve down. You shouldn't push it down all the way, only about a half an inch will suffice.

What the adjustment does is reduces the amount of throttle opening needed to produce boost, by shortening the travel length of the valve lever that is attached to the throttle. When properly set, it will allow about 11 to 11.5 PSI at wide open throttle, or just short of wide open throttle. In any circumstance you may also notice that your GTP is a little quicker from a standing start after the adjustment.

SCAN VECHICLE FOR ANY SUPERCHARGER BOOST SOLENOID FAULT CODES.AND CHECK FOR LOOSE OR BROKEN VACUUM LINES GOING TO SUPERCHARGER BOOST SOLENOID THAT WILL CAUSE NO BOOST PROBLEMS.

Your transmission for the GTP should be the 4T65-HD. If in fact it is not then that could very well be the problem. The 4T65-E is for the other 3.8L naturally aspirated models.

Verify that the supercharger belt is tight enough...check the tensioner and idler pullies.

Then check your vacuum lines on the boost solenoid.

Well, the short answer is "yes". But - it isn't nearly as simple as just bolting the supercharger onto the intake and VOILA!, now you're supercharged. The procedure that you're inquiring about is commonly referred to as a "top swap", and there are numerous parts you will need for both engine as well as the transmission. Why the transmission? Because the GT and GTP use different gear ratios and the GTP has a 4T65HD as opposed to the 4T65E that is in the SE/GT. You will also need to have the PCM reprogrammed to accomodate all of these changes.

HERE is a great website that has a ton of very useful information, regarding this and many other Grand Prix topics.

Hope this helps and thanks for using FixYa!

Check the vaccuum lines to the super charger boost control valve located on the back of the supercharger closest to the air cleaner opposite the pully. If you are not getting vaccuum to the boost control colenoide follow the vaccuum hoses back to the boost control switch and check for engine vaccuum at the switch.

No leak, it may be time for a service to your supercharger. There is maintance that most people don't know about and the bearing to the supercharger's wear out and then has play. The bad things is with the play the lobes in the supercharger starts to rub against the housing and then the tolerace clearance is larger then when the car was new. Long story short, time to have your supercharger rebuilt before it fails and kills the engine too. There is an other way you can look in too, here is there web page http://cartuning.ca. Good luck