I installed a fass 150 right out the box this weekend along with a sinister diesel sump my concern is my fuel pressure is all over the place at idle it varies from 21 to 12 and cruising down the road at 60 it varies from 18 2 12 at wide open with smarty on 4 and the edge on 0 I can pull it down to 12psi then it starts fluctuating all over the place... Pretty much I cud have put a stock one back on and been money ahead!!! Ne1 have ne advice or troubleshooting steps be advice wud b helpful. Details of my truck is n my signature

 

Check your return valve spring in the fass. You may either need a new one or to stretch the spring to make it hold pressure better. Where do you have the fuel pressure sensor located?

 

Alright I'll try that today And the sensor is n the side of the elbow that goes in my vp until my t fitting gets here

 

In the banjo bolt? Do you have a snubber or needle valve connected to it? If no you are experiencing water hammer form the VP and that's why your pressures are all over the place.

 

Well I drilled out a 1/8 hole in a jic elbow and put my gauge right by the pump since from what I read the sensor needs to b as close as it can to the vp. My ignorance but what's a snubber

 

Here is a snubber.


My pressure sensor is mounted 1 foot back from the VP. I have no snubber but have no pressure issues either. It holds strong at 18psi with an occasional jump to 19 and a drop to 17 under acceleration.

 

Alright thanks ghostman uv been a huge help on this site!!! Is that messing with nething my sensor being to close to the vp

 

without a snubber you will see the pressure fluctuations you are experiencing.

 

Alright Ill c if the parts store has one if not I'll get one ordered. In another note I took the ball and and spring out ball looked fine spring was about 1 in long I stretched it to about an 1 1/8 that moved my pressure up a bit but still everywhere so I'll try the snubber