When air line is attached air blows freely through trigger valve. There appears to be a ball and seat mechanism. If so, is the ball and seat replaceable? Bryan

yup,,,

I have seen this on dewalt and p/c guns. Usually caused by trigger valve but you mention that trigger valve is new. If the headvalve does not seat correctly on the top of the cylinder, the in-rush of air will leak past cylinder seal and push down the piston (feels like you fired the gun ) . Difficult to pin down the problem but could be headvalve is sticking slightly open. I would suspect headvalve orings too tight or spring in head is weak or cylinder in head is worn. Easy to check. Remove the head and push in the headvalve with thumbs. The valve should be stiff to depress but return freely. Check that the cylinder in the head where the outer headvalve oring makes contact is not scratched or worn. If scratched, sand with fine sandpaper till smooth. If worn and depressed, replace head. If spring feels weak, stretch it a bit pulling it apart. Lube cylinder /orings with white grease. Untill you find the problem, do not load nails untill after airline is connected. On the dewalt guns, firing when air is connected is due to the trigger firing pin orings worn. You could check this on your gun by spraying soapy water on the trigger valve under the trigger then connect the airline. If air is blowing out the trigger when you connect air, most likely faulty valve. Good luck and let me know what you find out on the unusual problem.

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All things considered, maybe apply air pressure and stick the unit under water in a utility sink or big wash tub. Air leaks would bubble like a hole in a tire tube.

Part # 097746 valve pin has a rubber surface that seals when under pressure. To replace this part, remove the trigger then two roll pins in the body of the gun just above the trigger valve. Remove the valve and check for debris or faulty part, replacing as needed (verify the the orings on the outer part of trigger valve are not cut, there also should be a spring pushing down on the valve pin ). If the valve pin is worn, also check orings within the gun for wear, including the largest oring around the cylinder seal. Good luck

Had the same problem on a 2006 pilot LX. Hot from rear heater because it comes from a separate heater core. Front heat low because ball valve faulty that controls coolant flow to heater core. The lever on the valve would move freely but the connection to the shaft of the ball valve was stripped. Ball valve may be located on the firewall under the hood. Ball valve very poor design.

This series of nailers are the most difficult to repair. Your nailer has twice as many orings as the norm. Many have said that this nailer is over-engineered. There are three areas that could cause trigger area leak. To make it simple, lets do one area at a time. Use soapy water around the trigger area to find actual leak. If air is leaking from actual trigger valve (ms719-2) and its counterpart, the cartridge (ms719-1) then these two parts need to be removed. Check for scratches in the metal of the valve. If scratched try to remove with fine paper or replace as necessary. Most leaks are due to faulty trigger valve. If air is not leaking from actual trigger valve then remove the dump valve (mn120-5) at the back of the head of gun. There should be two small allen screws then metal lid, then spring and oring. Pull out dump valve and make sure all the orings are in order. This valve should be able to move, not too tight. Use silicone paste lube on all orings (available at Lowes in plumbing department, Danco brand used for faucet orings). Reinstall dump valve and related parts and check for leaks. If air seems to be leaking from bottom of gun neer trigger, most likely problem is cycle valve (mm419-1) and related vinyl seat. These two parts are in the valve housing under the trigger. This valve also moves within its housing and seats on a vinyl oring. This part could be clear vinyl or black rubber. New seats are clear. Inspect these parts for scratches/cuts and lube with silicone paste. Hopefully you would have solved the problem with trigger valve. Good luck with your repair and do not dispare, this is one of the most difficult guns.

Check if air is actually leaking from the plunger valve. (check with soapy water) If leaking from plunger valve check outer orings to cylinder guide and cylinder plate. Small cuts to these orings will cause leak by trigger. If trigger is actually leaking then replace vinyl ball and rubber seat. Good luck with your repair and post again if you have other questions.

return to dealer for servicing. Safety first.

After change fuel pumps per diagnostics still had problem with starting after fueling. Researched on-line and kept seeing purge control valve as solution. Mechanic didn't think it would do anything but filled up three times now and so far so good. part was $49 and he was nice enough not to charge for labor