I understand that but if the spring is weak it can cause many things. and I was told about the spring before I ordered the pump. so I think it's a known issue.

Which pump did you purchase? FASS 150.95 or a FASS 150.150? The 95's can have this issue but it is not common. The 150's don't at all but usually suffer from their own problem of being too loud. This of course won't really be an issue with your truck because it is as loud as mine is and I can't hear my 150.150 unless I stick my head inside the wheel well.

the 95. I can hardly hear the thing run when I cycle the key without starting just feel slight vibration that lets me know. I guess the rubber piece they put in it helps the noise too.

I have the 95/150 on my truck.. Idles at 15psi and never dips below 13psi at wfo.... I put my edge fp sender in the liine going to the IP under the hood.. Never a problem with fluctuation at all... let us know how the spring works out...

it maybe the edge, ive heard several of the electric sending units go bad or are bad from the factory, thats why im getting a mech. gauge asap. plus im upgrading to the 150 adjustable from fass as well. plus if you are running bigger lines and banjos, your pressure will be a little lower then before as well. picture water going through a drinking straw, now think of water going through a garden hose, the garden hose flows more water then the drinking straw but at less pressure, so itll drop it too, plus if you are running injectors, espeically big ones, itll suck more fuel as well, dropping pressure. let us know if the spring fixes anything.

now I have 16psi at idle and runs 12psi wot on level 5 no issues now and lays out a much healthier cloud of black smoke

Other than having the incorrect spring installed in the kit, I can count on one hand the times I have seen the spring be the actual cause of a pressure issue. They don’t get weak from what I have seen. NOW with the 95 series FASS…..we have found the PS-1008 spring to be a tad light for some. SO we send out a PS-1001 to put them in the 16ish PSI range.

I would defiantly suggest a snubber…..here is a link:

Auto Meter

The spring was weak and the new one Jason sent out works great. 16psi at idle now that things are settling in. Never drops below 13psi.. I would have bought one of these at the J&H Diesel drags but had just spent 9k on school fees and plan check fees for my house and was way strapped for cash. The Fass trailer and display was really helpful to see what it does. I will look into the snubber to protect the sender too.

I got my fass 150 used off a friends truck and havnt changed the filters yet. Is it a good idea to use the FASS filters or can i just cross the #'s over to a Wix filter? My setup demands fuel and my gauge is mechanical right before the ip and idles at 13-15. I throttle it and it drops to 10-12, i open it up.....maybe 8psi.

change your filter and drain the water separator and clean it.

FASS - Fuel Air Separation System - fassride.com