Engine/Transmission (1998.5 - 2002) Possible FASS issue

[MRoberts]

I noticed my fuel pressure was dropping a bit the other day. It has been awhile since I changed the filter and water seperator, so I thought that would take care of it.



Well changing them both out wasn't the answer. I used to run a steady 20 psi with a slight drop when goofing around. :-laf This past week, I noticed that after starting my truck, that I was in the 13-15 psi range. After a few miles, my pressure would climb up to its "normal" range, 19-20 psi.



Everything else seems completely normal, good performance and response. I have the 150/95 "full meal deal" system.



Any thoughts? Diesel Dan still around?



TIA!

 

[Midnite]

Could you be starting to gel up?

 

[magaliasram]

Is it possible the heater grids are pulling the voltage down? I know on my truck my fuel pressure drops until my altenator brings my voltmeter back up to the normal operating range. I can watch my fuel pressure drop each time the heater grids cycle on just a thought. I don't have a FASS either I am still running the stock LP second one in 166000 miles and still holds 16 psi at idle and pulls down to 12 at wot with my 10000 fifth wheel in tow. So I could be way out in left field here.

 

[MRoberts]

Could you be starting to gel up?

Nope, we have been in the 30-54 degree range. About 100 degrees warmer then you! Plus I use Stanadyne in every tank.

 

[moonranch]

A couple of weeks ago I had a similar problem. It turned out to be the "isolator" for the fuel pressure gauge. I opened the fittings a little bit on both sides of the isolator and everything was back to normal. Hope your fix is just as easy.

 

[Geno's Garage]

Was a different spring put in after you received it to raise the pressure. I have had two of these systems on my 99 trucks & do not see over 15psi on either. Also confirm that your gauge is reading correctly. Scott

 

[LowFly]

I noticed my fuel pressure was dropping a bit the other day. It has been awhile since I changed the filter and water seperator, so I thought that would take care of it.



Well changing them both out wasn't the answer. I used to run a steady 20 psi with a slight drop when goofing around. :-laf This past week, I noticed that after starting my truck, that I was in the 13-15 psi range. After a few miles, my pressure would climb up to its "normal" range, 19-20 psi.



Everything else seems completely normal, good performance and response. I have the 150/95 "full meal deal" system.



Any thoughts? Diesel Dan still around?



TIA!

Im here.....



Well you got some good suggestions above... but at the temps you are seeing, gelling is not your issue. Thicker, cold fuel can drag down a gague..... and then when it warms up, it will come back up to norm.



Scott makes a point... either you changed to a PS-1020 spring or you have an older FASS that came with one (2005ish build). Most dont make over 15 PSI on the ones we have out now.



My first suggestion is to always make sure your gauge is telling you the truth..... we get about 4 calls a day here that are solved at this step. See where that gets you and post back up... ...

 

[GCULP]

do you have a pre-filter before the pump, if so check that, I had similar issues and it was a small piece of debris in the pre-filter.

 

[MRoberts]

I haven't changed the spring in mine. It has read that psi since I installed it.



I have changed the gauge and isolator once since the install. The gauge was changed because it went south and the isolator was changed for appearance.



The thing that is strange, nothing has been touched on the system and all of the sudden I'm showing 10-15 psi at start up and then normal (20 psi) after it has been running for awhile.



I will dig a little deeper into it.....



Thanks for the input!

 

[LowFly]

I haven't changed the spring in mine. It has read that psi since I installed it.



I have changed the gauge and isolator once since the install. The gauge was changed because it went south and the isolator was changed for appearance.



The thing that is strange, nothing has been touched on the system and all of the sudden I'm showing 10-15 psi at start up and then normal (20 psi) after it has been running for awhile.



I will dig a little deeper into it.....



Thanks for the input!

Rebleed the isolator..... use silicon fluid (Comes in spray can) instead of coolant... . if air gets into the gauge side... it can cause funny things... .

 

[MRoberts]

Dan,



Thats a new one to me. Silicon fluid in place of coolant from the isolator to the gauge. Right?

 

[LowFly]

Dan,



Thats a new one to me. Silicon fluid in place of coolant from the isolator to the gauge. Right?

Yup... actually got that one from a dealer... . well in your neck of the woods.



Coolant crystallizes when exposed to air. Ever see a coolant leak on an engine where you see that residue? If this happens enough in an isolator, it can clog it up and limit the travel of the diaphragm. Talked to one guy this happened to.