Fass Lower Fuel Pressure When Warm Outside
#1
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Location: Vulcan, Alberta
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Fass Lower Fuel Pressure When Warm Outside
I put a new 150gph Fass Platinum on my truck a few weeks ago. I've noticed that when I start the truck in the am, and the outside temp is about 5C outside, I've got about 15psi fuel pressure. When I start the truck at the end of the day at work, and the outside temp is 15-20C, the pressure is about 12-13psi. When driving when warm out, it will drop to about 10psi under fairly hard throttle. Doesn't seem to matter if the tank is 1/2 full or full. Any ideas what would cause this?
#2
I wish I was as fine, as those who work the pipeline!
Could be the diaphragm in the fuel pressure sending unit. Try putting a shop light under the hood, pointing at the sending unit, over night with a 45w bulb on it. That will keep the sending unit warm. If the pressure is what it is when it is warmer, not a big deal. If it is the same the problem is not with the sending unit and may be somewhere else in the fuel system.
Easy test though.
I had sender issues with mine and had to put a second snubber on it. Low pressure readings. It was in the winter so it was always cold. I have an 18" line from the VP to 2 snubbers then my sending unit. After I added the second snubber, everything worked just fine. That was about 15k - 20k miles ago.
Easy test though.
I had sender issues with mine and had to put a second snubber on it. Low pressure readings. It was in the winter so it was always cold. I have an 18" line from the VP to 2 snubbers then my sending unit. After I added the second snubber, everything worked just fine. That was about 15k - 20k miles ago.
#3
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The only time I have seen fuel psi drop from temp was when I was on the interstate in over 100*F (38*C) and had less than 1/3 of a tank. I dropped about 1-2 psi.
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Thanks guys. I'll try and warm up the diaphram, don't have a 45 watt bulb in my trouble light, and I need to be careful I don't start a fire. I'm a little suspicious of the electric fuel pressure gauge, when I put the 150gph FASS in I went for a 10 mile test drive. The gauge was bouncing like crazy, ie hammering from the pressure. I put in a needle valve, which cured that, but it's entirely possible I did some damage to the gauge, although I was hopeing that 10 miles wouldn't have been long enough. Anyone know what gets wrecked on an electric gauge from hammering, the gauge itself or the sending unit (diaphram)?
#6
No clue if the VP44 has a overflow valve, so disregard if it doesn't
But I have had the same symptom on my truck and it ended up being a weak overflow vavle. I would have 18 psi when the engine was cold and it would drop to 14 psi when warm.
But I have had the same symptom on my truck and it ended up being a weak overflow vavle. I would have 18 psi when the engine was cold and it would drop to 14 psi when warm.
#7
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Summer temps create lower fuel pressure due to higher fuel temperature!
Thinner fuel. Every summer I notice start up pressure is 1-3 psi lower on my FASS 150 than was in the winter.
MY Isspro gauge was bouncing badly for months before installing a needle valve. This was 4 yrs ago and it still works well.... so no worries mate.
Every winter I have to tighten down the needle valve a bit (almost fully closed off) and every summer I can open it 1/4 turn.... also from difference in the the fuel density due to OAT.
RJ
Thinner fuel. Every summer I notice start up pressure is 1-3 psi lower on my FASS 150 than was in the winter.
Every winter I have to tighten down the needle valve a bit (almost fully closed off) and every summer I can open it 1/4 turn.... also from difference in the the fuel density due to OAT.
RJ
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#8
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#10
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Your 2 psi drop under heavy throttle also sounds normal. Particularly if you're towing heavy.
Falling much below 10 psi would worry me a bit. If it does drop lower, I would start to worry about my VP-44.
I have an 18 psi spring in my 150 gph FASS. Might want to consider that.
I never get below 15 psi....even when I was at 600 hp and racing at the track!
RJ
Falling much below 10 psi would worry me a bit. If it does drop lower, I would start to worry about my VP-44.
I have an 18 psi spring in my 150 gph FASS. Might want to consider that.
I never get below 15 psi....even when I was at 600 hp and racing at the track!
RJ
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