I have the same problem in my FX

I had a slow that almost drove me to trash mine the other day. Mine ended up being a leak form behind the bottle and first reg gauges. I had taking it apart close to ten times before I figured it out. Also make sure it isn’t leaking between the front reg and body. Mine also had the wrong o-ring there form the factory.

If there are more o rings than I can count on my fingers, then I am not a fan. I enjoy shooting not trouble shooting.....

I would inspect the poppet and seat. If it has no blemishes, I would replace the tiny oring on the end of the valve rod, cross my fingers, say a prayer then reassemble it. Leaks can be frustrating. I couldn’t find in your post where you heard the pssssst come from.

There's quite a few orings on the impact yes but far from all are under pressure all the time to cause this.

Gauge xrings
Small oring at the end of valve pin
Orings on valve house
Two outer orings on small end of plenum
Inner oring on plenum that seals against the valve rod.
Regulator orings

Off the top of my head, I'd get some leak detector and check these areas.

Nate, I never actually checked, bu

Glem.Chally said:

There's quite a few orings on the impact yes but far from all are under pressure all the time to cause this.

Gauge xrings
Small oring at the end of valve pin
Orings on valve house
Two outer orings on small end of plenum
Inner oring on plenum that seals against the valve rod.
Regulator orings

Off the top of my head, I'd get some leak detector and check these areas.

Click to expand...

to add onto your list of o rings as a part of the air pressure, you have one under that tiny pan head screw on the right side behind the vent hole(it’s the one screw some people never swap out when doing a stainless fastener conversion), the bottle itself has 3 o rings, and this next area ive never verified, but it’s the two plugs at the front and one at the rear of the trigger block. The front is hidden by the bottles Dowty seal, and at the rear it’s hidden by the hand grip. It’s the tunnel that FX drills thru, that is the pathway of air pressure to the regulator. Not looking at the parts diagram at the moment, but I could’ve sworn there were o rings under those screws.

To the OP- what kind of valve spring are you using in your gun? Factory or the lighter one that comes in the slug power kit? If you are using the lighter spring and DID NOT install that buffer rubber ball then your valve rod is over traveling, which will eat up that tiny valve rod o ring if it’s even still in there.

Drape a piece of toilet paper or light tissue over the cheek rest and have the sides cover the mag slot area. Do a dry fire. If that tissue blows up on the sides then that means your valve rod o ring is KAPUT

Also, check that o ring that goes on the outer groove of the front end cap beak of that power plenum. Some of the o rings that came with the pp kits did not stick out past the threads when you look closely at the threads. Either the groove was machined too deep or the o rings supplied were not thick enough, and that’s a guaranteed leaker especially if the rear block flexes from setting it on a rear rest, pressure downwards.

is the gun a m3? i got a miniscule leak when i put the side mount gage for the second regulator, it took a couple weeks to drop from 200 bar to 0, still shoots if i air it up, so ill live with for now, but it is a nagging thing, didn't leak before that. might have to remove the side gage.