I have a leak at the fuel pressure damper. The screw (which purpose is to indicate pressure) did not feel loose, but I was able to turn it easily with a home-made angle screwdriver (#1 Phillips). Thinking that wasn't going the right way, I removed the unit and found I could tighten the screw snugly with about two more turns. (!!?) I believe I need a bunch of new crush washers to reassemble this (you have to remove the aft crossover fuel line to access the FPD), so I can't just put it back together and put pressure on it.

Meanwhile: I don't want the screw to vibrate loose (which is apparently what it did these last 19 years). Can I put Loctite on it? More specifically, if I removed the screw (to get to the threads) would something fall apart internally, preventing me from re-assembling the unit?

 

Now I'm thinking I was completely wrong.

The purpose of the screw is to indicate the pressure in the rail. The drawing suggests that it is screwed into a diaphragm with a little bit of play; on pressure the diaphragm moves out moving the screw head with it. By tightening the screw, I've just eliminated that play, eliminating both the indicator function and the (by keeping the diaphragm from moving) eliminating the damping.

More importantly, my problem is most likely a leak in the diaphragm, and tightening the screw won't change that.

So unless someone has some experience/wisdom in this area, I think I need a new damper. (~$112 at the dealer and eBay, ~$82 RockAuto aftermarket)

 

Also fully tightening the screw, so that the diaphram doesn't move, might stop or slow down the leak. If it's not closing it'll see a little less pressure right..

The pressure check function of the screw is a side effect, not it's primary function. Pretty sure you knew that, but others maybe not. No you can't use this inplace of the fuel pressure tests

Yep replace it. It's already out.

It doesn't really look big enough to smooth out injector pulses, but I'm sure the toyota engineers knew what they were doing. Just looks so tiny

And if you really want to try the locktight to seal the screw, like incase it's the cap in the diaphram instead of the rubber. Go for it, screw will either be long enough or you can press on the bottom side of the diaphram. Looks like a metal cap there to me.

 

I found the same problem with mine and no mater how tight the srew is it will leak. Just replace it. I got mine at Car Quest for the the same price as the dealer. It was an OEM part too.

 

Thanks. I put mine in last night; works great. $113 for the Denso part from my excellent dealer, including 6 crush washers. (2 for the damper, 4 for the aft fuel line cross-over I had to remove to access the damper.)

 

Here are some photos of the bad damper cut open. Note how the flexible membrane had pulled out of the crimp toward the top of the photo. There is no seal around the screw; fuel just slowly leaks out, and I was very lucky to catch this.

If you were to tighten the screw, it would pull the membrane snugly against the spring, defeating any damping. If the screw was simply removed, it doesn't look like it would affect the damping. The screw seems to be there solely to indicate that there is pressure in the system.

Note that the non-screw side of the membrane seats against the exit opening. When the fuel pump stops and if the input pressure drops, the spring would push the back of the membrane against the exit opening. Would this hold some pressure in the rail if the fuel line depressurized? Its a metal-to-metal seat, so I would be surprised if it could hold any pressure.

 

This damper is just like the ones used in household plumbing to prevent what is called "water hammer", this is the backpressure created when the flow suddenly stops from closing the tap.

Same principle effect happens when the injector closes, the damper prevents this surge from hitting the fuel pump.