Fass Low Fuel Pressure

[DBuck]

Hi,



I have a 2001 24v truck with about 95K miles. Truck is essentially stock except for Fass 150/95 I added 1 1/2 year ago after the VP-44 ate itself. Learned a lot the hard way about limitations in stock lift-pumps and lack of stock fuel pressure gauges. At that time, I also installed the Isspro manual fuel pressure gauge with the isolator kit from Geno's garage. With Fass and fuel gauge in cab, I consistently see 14. 5 psi pressure at idle, at 10 psi at WOT. I have about 10K miles on Fass so far.



Everything has been fine until about two weeks ago. I started noticing that in the mornings that is fuel pressure is a lot less than normal. It has slowly declined each morning. Now in the mornings when I start the truck, the fuel pressure is at 7. 5 psi. During my 20 mile drive to work, the pressure rises steadily and gets to about 13. 5-14psi (not quite the normal pressures from before) by the time I arrive. Living in the Portland, OR area our night-time temps are mild and gelling/thickening of fuel has never be a problem for me.



With 10K on the fuel filter, I don't immediately expect it to be dirty. Fass manual says 15-30K for filter changes. There have been no changes in the type of fuel (no bio-diesel, etc. ) I use. I drained the water separator and the fuel looks and smells fine. Also, I have heard no change in the sounds from the pump.



I am just curious if anyone has seen similar things? I have a hard time understanding why the fuel increases as the truck (and fuel) warms up. Especially when this never occurred before. Now that the pressure is getting down to the "danger" area when cold, I need to find this.



What is the real world experience with filter change intervals? Is this the problem and I can only expect 10K on a filter?



At this point, I suspect the fuel pressure gauge. I have a fuel pressure test gauge on order from Geno's to check the pressure at the VP-44 inlet (same place as my in permanent gauge). I'll report back when I get it measured.



Thanks Everyone!

 

[LowFly]

I too would suspect the gauge. Actually i would check the isolator on the gauge. They are notorious for going bad. As far as the PSI getting steadily higher throughout the day... that is because the fuel is getting warmer and is thinner, allowing it to move more freely in the lines.

Check the gauge and let me know how it goes.

As far as filter change intervals... . the manauel is correct up to 30K is fine. The water separator is actually serviceable and the fuel filter needs to be changed between, 15K-30K. I doubt this is causing your issue nor do i think that your fuel is gelling. It hasn't been that cold as of yet.

 

[JKreiss]

Very interesting DBuck, i'm going through the exact same thing with the 99'. I was going to tackle the isolator this weekend but was too busy with Cab clearence lights on the 04. She likes to rain on the inside when it's raining outside:-laf Keep us posted on what you find.

 

[DBuck]

I got the pressure gauge from Geno's. Connected to the VP-44 at the input port shrader valve. I get almost actually 15 psi. So clearly there is a problem with the in cab fuel gauge.

LowFly, you mentioned the isolators are common failure points. What causes them to fail, they seem pretty simple to me? Is there a good fix for this? The gauge has only been in the truck for less than 2 years. I really don't want to change out the $70-80 isolator that often.

Thanks

 

[LowFly]

you dont have to change it but it needs to be serviced. From what i understand, the isolators are filled with glycol. This needs to be changed on a regular basis (I do not know what the interval is) When you do change it you also need to bleed air from the isolator.

 

[hbowers]

I have found that the isolater has to be filled with plain old anti freeze every now and then. the antifreeze somehow evaporates or something. try taking the tubing off the isolater and adding some antifreeze. I think your pressure will come back to normal.

hbowers

 

[JKreiss]

that's what i ended up doing. I took everything apart, emptied out the isolator and refilled with 50/50 antifreeze. New tape on all the fittings and all put back together. Fuel pressure is right back to where it should be.

 

[jhoughton]

I had the same thing happen and it ended up that the isolator bellows had pushed beyond half way. Take the four corner screws off the isolator and make sure the bellows is towards the engine. Then reassemble and fill properly with anti freeze. Make sure you have no leaks and this should correct the problem.