My 99 3.8 supercharged grand prix has code p206 and i have already replaced the injector and the problem remains its also causing a misfire on cylinder 6 i have checked wiring and looks good as far as i can tell as well as all vacuum lines going to the fuel system at this point im just lost

As you see I provided you the models you can apply the transmission :The 4T65E-HD (code MN7) is a heavy duty version of the 4T65-E used with more powerful engines such as the LS4 V8 and L67/L32 supercharged V6. Applications: 2.93:1 MN7 Pontiac Bonneville SSEi L67 Chevrolet Impala L67 Chevrolet Monte Carlo L67 Pontiac Grand Prix GTP/GXP Buick Regal GS Buick Riviera L67 (97-99) So ,yes you can!

Well, lets see....there is no "Grand Prix Turbo" so I am assuming that you mean that your Grand Prix is a 3.8L that is equipped with a supercharger.

The supercharger bearings are lubricated with synthetic oil that is contained in the supercharger gousing. It is self-contained and does not rely on engine oil for lubrication. You can check the oil level in the supercharger by removing the plug in the supercharger housing (see diagram)

There are a whole lot of things that can cause a cylinder misfire (including electrical faults)

Electrical problems can be fixed. However, an electrical fault cannot be PROVEN without FINDING the electical fault. My experience is that once an electrical fault is found, it isn't nothin' but a thing to fix it. 99% of the problems with electrical faults is finding it.

The "diagnostic machine" is not any better than the tech that is using it. Did the tech perform an injector balance test? Did he try swapping injectors with another cylinder? Did he perform an engine compression test so he can compare the compression on #4 to the rest of the cylinders? Did he perform a running compression test to check for weak or broken valve springs? Did he check for an intake manifold vacuum leak at the #4 intake runner? (Supercharged 3.8L engines are pretty bad for blowing intake gaskets). Did he bother to check the freeze frame data to see what conditions are causing the misfire? or is it missing so bad that it is obvious while idling in the shop?

Or did he just throw a bunch of parts at it and file a cost-based waiver application....I have seen MANY incompetent techs do this.

I would NEVER accept "electrical problems" as a valid reason for not getting a misfire code fixed. My answer would be don't waste my time or my customer's money trying to blame your incompetence on some "mysterious" electrical problem...PROVE IT!

The evidence suggests that you do indeed have a bad fuel injector. Inspect the wiring to make sure you don't just have a poor electrical connection there - then if that looks good replace the injector.

Misfires can be caused by several things including all the parts you have already replaced as well as faulty ignition coils, faulty injectors, vacuum leaks and engine mechanical problems such as low compression.
With the proper equipment, injector operation can be verified by performing injector balance tests, where the operation of the injectors in the misfiring cylinders is compared to the other cylinders that are not misfiring.
Also, engine mechanical failures such as bad piston rings or leaking/burnt valves can be diagnosed with a simple compression test.
An easy (and very inexpensive ) way to verify ignition coil operation is to swap the coil from the misfiring cylinder(s) with the coil(s) from the cylinder(s) that is(are) not misfiring. Then clear the fault codes and drive the vehicle. If the same cylinders are still misfiring, the coil is not the problem. If the misfire moves to the cylinder that you swapped with - replace the coil.
Sometimes, injectors can also be tested this way, but on most GM V-6 or V-8 engines, this is not practical due to the labor involved in "swapping" injectors.

It's a possibility the injector is the problem. It may not have the psi it needs, therefore the cylinder could be misfiring, or the injector could be letting too much fuel in. Before I change the injector, I would try to have someone to clean the injection system to see how it works. The cleaning around in South Carolina is $99-$149 depending on where you go.

There is no wastegate.

Change the spark plugs and pay special attention to the plug on bank 3. Look for physical damage on the electrode...cracked, bent etc.
Use Autolite 605's copper core gapped to .055" and NEVER run less than 92 octane.

Ac pressure sensor high voltage or o2 sensor bank 1 sensor 1 sluggush.

the code reader should tell you what cylinder it is if so switch the injectors around to see if the misfire moves to a different cylinder if it does you have a bad injector

try this link
http://www.ebookspdf.com/search/1998+grand+prix+gt+service+manual