Bottom Bracket Cable Guide
 

I have been having some poor shifting in the front lately, and during the investigation, I took a look at the guide to make sure it was not gunked up. It did not look bad, but I put a little lube in the groove the cables run in. However, the FD cable seems to be rubbing right on the paint just past the end of the guide. The guide is a purplish color, which the internet indicates is a standard shimano cable guide. Is there a cable guide that has a longer groove for the FD cable so I can a) keep the cable from wearing through the paint down to the metal, and possibly improve shifting?

you could also use a piece of inner liner from the housing ,just put it over the cable or a cable donuts ( the one you see on cable on some bikes ) you can get from your LBS .

Is the cable giude perhaps worn to the point where it is allowing the cable to contact the paint? Perhaps a replacement is in order.

If the cable run is really that poor and the cable guide is in good condition the easiest solution is to install a clear paint protector pad in the area you're concerned about. They come prepunched in round and rectangular formats for installation on new bikes and your dealer can probably pass you a couple. Clean the area with alcohol first.

Another solution is to scrounge up a small piece of flexible plastic. Loosen the guide, and trap the plastic under it extending it into where the rub is. Tighten the guide and it'll stay that way for eons.

Also check that your FD cable is attached to the FD pinch bolt on the correct side and routed correctly. The routing for the FD on many of the new dual-pull FDs varies. If coming from the bottom, it may require threading through a pivot first and then clamping into the pinch bolt on the outside of the bolt. If your FD shifting requires undue force to shift, that may be a clear sign of bad routing or pinch-bolt clamping. A simple shift of an FD cable from one side of the pinch bolt to the other, can sometime increase torque at the pivot by 50% and reduce the amount of cable pull (which is likely to solve the over-shifting issues if you are encountering them). This might avoid undue wear by the cable on the frame.

Properly installed Shimano and Campy bottom bracket cable quides come pretty far back and around the bb shell for the non-drive side (front derailleur cable) guide groove so I wonder if you have the guide bolted into the correct hole in the bb shell. Many frames have a couple of holes at the bottom of the bb shell, one for the cable quide and one as a drain hole. If the guide in the right one?