I have a 2 year old FASS 150 GPH pump for my truck. The filter has recently been changed and water seperater recently drained.

On cold mornings the fass has trouble holding proper fuel pressure. It dances around from 1psi all the way to 20psi.

This only happens when it is cold outside (45 and below) once it warms up it doesn't have the issue.

I monitor the pressure with my edge programmer.

I have checked the power wires and connections to make sure it is getting enough power.

Does anyone know what causes this fass to act erradically?

The VP44 has about 60,000 miles on it and works perfectly.

And this issue only occurs when it is cold outside. Didn't occur once all summer.

Let me know what you guys think.

 

hi there,

If you have a garage try parking it in there for a night, see if it does it still. and how long do you let your truck warm up for in the mornings before driving?

 

I do have a garage, however, my truck is to big to fit in it .

I usually let it warm up for <1 minute when its 45-50 and above.

Anything below that I let warm up longer.

The PSI seems to fluctuate more during acceleration. Once at cruising speed it doesn't seem to do it as much.

THanks Guys

 

are you leaking any diesel on the ground. check to make sure all is tight it sounds like you have an air leak. Did you install the system or was it done professionally? do you add any additives to your fuel? These systems can drive a sane man insane

 

No fuel leaks at all. Not even the tiny leaks that attrack dust. I haven't put any fuel addatives in all summer.

Its really weird because it only does it when it is cooler out. And yes it is driving me crazy.

I don't want my VP to be starving for fuel, it has been running well so far.

 

Could it be your grid heaters cycling, dropping the voltage to the Fass causing it to run slower?

Sort of like how the headlights will dim with the grids.

Grids cycle below 50 F.

Older batteries might contribute to the problem.

 

Is this just recent? I would agree with the Grid heaters, however it shouldn't pull the PSI down that much...3 pounds at most (at idle).

How much fuel is in your tank? I was thinking gelling, but 10 degrees (celcius) is still too warm for that.

 

Could it be a bad fuel pressure sender?

 

This is what I would lean towards. If the grids were pulling it down, it would only affect it sub 30mph. Beyond that, they aren't active. And besides that point, the most I have ever seen the fuel pressure drop because of the grid heaters was 5 psi, and that was with a bad OFV and on a single battery.

 

Its possible that its the grid heater, however, I am not 100% convinced. Because it drops more rapidly upon acceleration. While sitting at a light it fluctuates up to 30 psi.

I don't think it would be the fuel pressure senser either because when I get off work and its 70 degrees out I don't have the problem. The FASS holds at 15-16.

Is there anything in the VP44 that would cause it to flucate or act differently depending on the temperature. Once again, its got about 66K on the VP, no codes and no issues.

The batteries are about 2 years old and have no problem starting the truck in any weather.

This thing is driving me crazy.

Thanks Guys

 

I'd put a mechanical FP gauge on it and see what you get.

 

Mine has done the exact same thing for the past 2 yrs.Its just cold fuel.Nothing to worry about.If you drive it long enough and give the fuel time to circulate and warm up it will settle down and hold a constant pressure.

 

That would not be correct. Fuel at 10C/50F should not be gelling. I've been in -45C with mine and no gelling, fuel pressure never drops much.

Listen to the pump. If its an older FASS, its easier to do. You will hear when it slows down due to the grid heaters. If your pressure drops with no change in sound, I'd be looking at your sender for the gauge.

 

I am actually leaning towards the grid heater issue more than anything else.

The reason being is because this morning it was around 50 degrees out which is warmer than it has been. The fuel pressure was still all over the board but def not as much.

I believe the grid heater isn't working as hard on the warmer days which allows the pump more power to keep the proper pressure.

I might try a couple things.
Either switch my batteries to make sure they are both doing the work.
Or
Starting the truck cold then unplugging the grid heater to see if the pressure is still all over the board.


The fuel pressure being all over the board doesn't bother me until it drops below 2 psi, or over 30 psi.

Thanks guys

 

My truck just started doing this too. On these 50 degree mornings when the voltage drops due to the heaters cycling my fuel pressure sits at 5 psi. I can clearly tell the difference when I turn the key on these cooler mornings. The pump sounds sad in comparison to later after the truck is warm. Like it's working much harder when it bumps the fuel pressure while the wait to start light is on. The bump from the pump on these cold mornings is only raising pressure to about 2 psi, whereas after having been driven or on a warm morning, the bump will raise the pressure to about 5. When the heaters cycle and the voltage increases, pressure increases too. if they cycle back on, pressure decreases. Once I begin moving 15-25 mph and they stop cycling, pressure is about 10. This pump is pretty new, installed in June. I have a FASS DDRP to install, but would like to figure out why pressure isn't holding steady first.