I have a NR 90GC Hitachi nail gun, it needs excessive pressure on contact tip before it will fire, any suggestions? Thanks.

The nose tip is most likely stuck in the ready to fire position from too much force being applied when nailing. These guns are small and sensitive to forces being applied. Try bumping it to see if the nose tip is retracting and compressing with each bump. Unplug and unload the gun before trying to pull the tip of the nose to retract if it is stuck. Check for foreign objects obstructing the trigger and safety mechanism

Easy to check. Remove nails from gun and connect to air supply. Using hard rubber pad or soft wood depress and hold trigger and push nailer safety against pad and hold there. The gun will fire but the driver will stay down until you pull back on the gun and relieve pressure on the safety foot. With driver down examine the tip of the driver. It should look square and should extend about 1/4 inch or more past the nose. If tip is broken replace driver. If lots of air is leaking past the nose during test, also replace the lower bumper. Good luck

If your using refills that have wire holding the nails together.
Check to see if bits of wire, debris is collecting in around the striking hammer. I switched to paper and never looked back. Must have gone through 5k worth of nails and rarely jams. Other things to check,
1. Check the striking hammer, make sure it is not bent or damaged.
2. Check air pressure, Low pressure can cause jamming, misfires.
3. If the tool needs pneumatic oil, 2-3 drops before you start good rule of thumb.
4. Check spring return. Sufficient pressure must be maintained or the nails will not feed properly. Misfires, incorrect feed, jamming etc.
I had a Hitachi brad nailer and it was horrible. Fire 1 brad nail would jam or misfire. Did everything I could think of nothing worked. Put it up, got a Rigid brad nailer and never looked at the Hitachi again. :)
Sometimes you just get a lemon! (PS I understand you have a framing nail gun. Brad nail gun above is used for an example)
Hope this helps

Sounds like you have worn valves or damaged o-rings. Unfortunately Hitachi does not make a rebuild kit for your nail gun. If you go to www.ereplacementparts.com you can find an excellent breakdown of your tool and either order the parts you need there or use the part numbers to search the web for prices and availability. Your tool is on the old side and some parts are no longer available.

If every nail is stopping at the exact same height, a likely reason is the tip of the driver is broken off so it's not long enought to drive the nails all the way to flush. If the height of the nails is slightly different you may have worn or broken o-ring(s) inside the gun and air is leaking around the driver's piston or elsewhere in the gun so that the driver isn't getting full pressure. You can take the gun apart and inspect the o-rings. If you push the driver all the way down the tip should come flush or slightly past the end of the nose piece (not the safety tip). Parts are easy to find online or at a service center if you have one nearby.

lbrication

I have a older Hitachi 3 1/2 full roundhead nailer and on my there is a button on the front below the head at the end of the nails that you push sideways and hold and slide the nail gun tip up or down. There should be grooves across the front of the tip.

Trigger may be dirty, as an electrical switch the contacts can be intermittent. Also check to see if the safety plunger is set to correct depth and moving freely. Dirt can build up here......

Yes, BUT the paslode Round drive nails and known to cause driver jamms due to the excessive paper used in the spacing of the nails.

The NR83a has an adjustment just below the triggering plunger. It is a 6mm hex head bolt with a locking nut. Loosen the nut and adjust screw out several turns and re-test. Make adjustment as necessary. I have seen many of these gun without the locking nut which allows the bolt the adjust itself all the way down. AS parts wear this screw needs to be adjusted. The pushing lever and the plunger are wearing smaller/shorter, that is unless the locking nut was missing. Remove gun from air supply for safety when making adjustments. Good Luck an email if you have other qustion about this gun.