Cylinder 4 Misfire (Fuel Injector?)

[Singlealt]

I have a naturally aspired 06 Grand Prix that is throwing the code for a misfire on Cylinder 4. I've swapped wires, plugs, and coil pack, but it is still misfiring. I actually have visually checked the plug and it's firing as expected, so I don't believe it's on the "fire"side.

I'm now thinking it's fuel related. This car has 300k miles on it and still has the original injectors, so I'm wondering if one of those have failed. My plan was to swap a couple and see if the problems move or to disconnect and reconnect the wire to it. However, I'm having trouble figuring out how to remove the injectors or operate the clip on the wiring harness.

What's y'all's ideas about what may be going on? Also, can anyone explain to me how to remove those injectors?

A could of other pieces of info. I checked the compression all the way around. The front 3, and rear left were all around 115-120. Cylinder 4 (misfiring) and Cylinder 6 (beside it) were up around 155-160, if I remember correctly. What would cause a higher compression on those two cylinders? Also, I've had what I suspect to be a lifter ticking for a while. I looked at the valves and they all seem okay, so I've just let it ride due to the complexity of fooling with the lifters in this car.

 

[Scottydoggs]

my 98 injector plugs had a metal bar on one side, push that bar in and it unlocks the plug. no idea if they are the same on a 06 tho.

 

[BillBoost37]

The 06 will have a colored safety tab you need to sneak back or out with a pick/small screwdriver. Once it's out/backed out a bit, you should be able to push down on the piece it kept from being pushed down and then pull the connector off. Then you need to remove the 4 10mm nuts holding the rail down and from there you should be able to get them.