My 16g straight 21/2 finish nailer does not fully retract the plunger so that it does not come back above the next nail head. It now fires as a single shot instead of semi-automatic

Is the driver blade retracting enough to let the head of the finish nail fully advance into the nose?

There are two issues that people have with nailers that sound the same however are totally different. Firing more that one nail at a time can be taken as; two nails being driven with one fire or the nailer vary rapidly firing a second time almost instantly after firing the first nail and each time only drive one nail. Problem of double fire (either type) is very common with nailers (the gun very quickly fires twice), however two nails at once can only happen if the wrong gauge nails are used in the gun. A 15 g nailer can very easily pass two 18 g nails or, with more difficulty, pass two 16g nails. To help prevent the driver blade from hitting two nail heads at once, most drivers are slightly tapered at the tip so that the driver will hit the first nail and the tapered part will push the other nails back into the rails slightly. Remove the head of the nailer and pull out the driver. Measure or compare the thickness of the driver to the thickness of the nail head. If you are sure that you are using 15 gauge nails, check the driver for taper. The tapered part should face the rails. If not tapered, try carefully grinding a taper keeping the tip cool so that you do not effect the hardness. You could also check for other brands of 15 g nails with slightly more spacing between the nails. There is a big difference in quality among brands of nails. Good luck with your repair

You have a obstruction in the path of the plunger taake it apart and clean it.

first make sure you are using the right guage nails. then I would look at the condition of the driver to make sure not bent, also look for a broken nail in the magazine area which will also cause this, lastly does the piston/driver "fall" in the cylinder?? there should be some resistance against the o ring, if not then it could also cause your described problem,

Argh...

Had the same problem, but only after about 4-5 nails. Once it jammed 4 times in a row - very frustrating.

I read the manual, took the unit apart, checked the driver - it was straight. I took a file and filed the back end of the driver down a bit so it would miss the second nail and so far it seems to be working famously.

Great unit...

i found this happening to me and i oiled (light oil like 3 in 1) the driver (hammer) in the tip. that way it could retract and drive the next brad.

a bit of air tool oil might help, make sure you are not getting condensation in the line, otherwise you may have to dissassemble to clean

firing pin called the driver is probably broken or needs new seals max air pressure 125 psi senco sells repair kits

There is a number of reasons that this will happen. Is the driver (plunger) physically stuck? Take a small screw driver and see if it can manually be pushed back. It may also be a broken head valve spring, or a stuck head valve (you have to remove the rear cap to get to these parts) Maybe this unit just needs an O-ring kit. Try these things and let me know