I changed my fuel filter today and shortly after getting the truck running again I noticed the fuel pressure gauge was not reading? I pulled the line from the isolator to the gauge and was getting nothing coming out of the isolator with the truck running. The truck runs fine so I am guessing there is air in the line between the fuel filter and isolator. It has been several years since I installed the gauge. Can someone remind me of the easiest way to purge the supply line that runs to the isolator?

 

I would check your lift pump for proper operation.

"The truck runs fine" statement concerns me, if your vp44 is sucking fuel it will seem to run fine for a while but you can damage it pretty quickly running it on a dead lift pump.

 

I think that's pretty normal. That's what my mechanical gauge does after a filter change. It should pressure back up after a run or two in the truck.

 

My fuel pressure isolator leaked in the very beginning and once it was really low my fuel gauge reading dropped of completely similar to yours. Without the gauge side of the isolator full of water it will mostly just compress the air in the line. I just had to remove the little elbow right on the isolator and fill it up there, didn't bother to somehow fill the teeny line running to the gauge and it read 14-psi with my walbro pump. If you fill that reservoir and the gauge still doesn't read you could either try to fill the little hose too but that would be a but of a hassle and likely won't make a difference.

I just read your post again and saw you asked about the supply side, I just bumped the starter to get the pump going then cracked the fitting at the bottom the isolator and bled off the air I could and it worked fine.

 

The isolator should have a "grub screw" for bleeding the fuel up to the isolator. It's an Allen head screw, be careful there's a small ball bearing under it and if you remove it the ball will fall out and the screw will no longer seal.

 

I already have a Walbro electric pusher pump on the truck so the full supply should be fine. I will go out and try to look for the bleeder on the isolator and see what happens.

 

Well I used the bleeder on the fuel side of the isolator and I now have psi reading on the gauge? Right after I started the truck back up after changing the fuel filter I had 15psi. Then the truck died out a few times I am guessing because of air in the lines. After cycling the fuel pump on a couple of times I got the truck running and that is when I noticed my pressure gauge was dead? Seemed kind of odd. And now that it is only reading 2psi it gets even better?

 

If you "bump" the starter, only just engage starter but don't start, the LP will run for 25 sec. This should give you enough pressure to bleed the system. You may have to do it a couple of times now you have air in the system.

 

I have bleed the fuel line and still can't get past 2psi on the fuel pressure gauge. After some research, I think the fuel filter is the problem. I think the AFE filter I got from Summit is a 3 micron and I read elsewhere not to go below 7 micron. I am going to pick up a Fleetguard filter (that is what was in it before) and see what happens.

 

That could be it you never know, are you sure the walbro didn't fail? Can you hear it?

 

Make your life easier, ditch the isolator and put a coupling in it's place.
Isolators are nothing but trouble and totally unnecessar with a good plumbing job.

 

As much as I hate to, I might just have to try that. I installed the Fleetguard filter and just get a constant 2psi on the fuel pressure gauge. I drove the truck a few miles around the block and it drives fine with plenty of power. I know the Walbro fuel pump is working because I can hear it when I bump the starter and leave the key on. At this point I am thinking something is wrong in the isolator. Are they pretty simple to take apart, clean, and put back together?

 

i have a racor 2 micron filter in my system, no problems!