You're going to have inconsistent fuel pressure for a few reasons...all related to the design "features" of the fass setup. 1) When the fuel is hot, it'll flow past the ball more easily. Hot fuel, lower fuel pressure at the engine. 2) The ball needs to move in and out to regulate, but the ball and spring coils rub as they run forward and back in the cavity. This rubbing causes hysteresis. It'll always tend to lag and then overshoot because it's not a frictionless system. 3) The ball develops grooves, so it can't seal perfectly. So when you are parked the return line flows backwards (we can't stop gravity) and you get air back into the pump and the pump may even loose prime unless the whole setup is lower than the level of fuel in the tank. As those air bubbles work their way back out of the system the ball is going to jump around. Their new "flow through regulator" is actually a conical piston with holes. It is leaky by design, so it addresses #3 by loosing prime more easily, but repriming at starting up more easily (leaks in both directions.) The only way to solve the issue is to feed the fass from a sump and then have the return go through the original draw straw, (not the filler neck) back to the bottom of the tank. Alternatively you could use a dual port sump and return to a sump. Or have everything go through straws. You just can't suction from the bottom of the tank and then return to the filler neck, up high. That way the loop won't loose prime when the truck is off. The whole problem with the system is a high return to the filler neck. Unfortunate but you have to be smarter than the marketing, which makes you smarter than their tech support too. When you buy the thing, it's the greatest thing on earth with a lifetime warranty and priced accordingly. But when you discover the limitations of the system and you've already cut up your filler hose which is no longer made, you call them on the phone and they are a bunch of jackwads. "But muh bucket test."
So I have my fass plumbed into a 100 gallon fuel tank in the bed that gravity feeds to the fass. Here is a link to the video about my setup. czcams.com/video/BUiWKP96g0A/video.htmlsi=oFKwN54daen7MWk8 I already have the flow thru regulator and I mainly have problems with fluctuating pressure when things are cold. 0⁰ F and colder. This is my second fass pump on this truck. The first one was flawless until the motor quit. This replacement one was good for about the first 50,000 miles until this started happening. Moving forward I bought several electric heater to put into the tank and fass and might run coolant lines to the fass. I also bought the fass external regulator and want to try that out and see what happens.
@7 if your fass is mounted below the tank, you shouldn't have the loss of prime issues that I mentioned. That said, a bed mounted tank isn't the reality for most fass/airdog installers. Lifting my bed to run a dedicated return hose from the fass to my spare draw straw solved the loss of prime when parked issue. I'm drawing from the bottom of the tank and returning to the bottom of the tank, so there's no way for air to enter the loop. The filler neck return is just not a good solution from a hydrodynamic design standpoint, but they do it for convenience. I'm betting 99% of fass customers have loss of prime due to drainback, don't know it, and are ignorantly happy. The truck still starts so you wouldn't ever notice it without a pressure gauge. Also, I discovered my suction side filter (Donaldson P551001) is a great filter, but uses an internal standpipe on the clean side. This traps air in the filter, causing subsequent loss of prime issues. I modified my filter by drilling a small hole at the top of the standpipe. In the future, I'll adopt similar but non-standpipe models on the suction, water separator, coarse filtration side: Donaldson P550847 or P55800, Baldwin BF1212 or 1268, etc.
How are those bearins on that motor? Mine started leaking out the weep hole and pulled the motor apart and found the drive end bearing shot out and the shaft grooved where the oil seal rides.
I did ya, I got the issue solved now, I installed the fass flow thru regulator and my fuel pressure is nice and stable now. I'll upload a video about that soon as I can
@@tdm8817 nice! I called fass the other day and they told me that bending that spring is the best way to fix it and that it wouldn’t hurt anything to leave it like that. Actually the guy I talked to said his truck has been like that for 5 years
You're going to have inconsistent fuel pressure for a few reasons...all related to the design "features" of the fass setup.
1) When the fuel is hot, it'll flow past the ball more easily. Hot fuel, lower fuel pressure at the engine.
2) The ball needs to move in and out to regulate, but the ball and spring coils rub as they run forward and back in the cavity. This rubbing causes hysteresis. It'll always tend to lag and then overshoot because it's not a frictionless system.
3) The ball develops grooves, so it can't seal perfectly. So when you are parked the return line flows backwards (we can't stop gravity) and you get air back into the pump and the pump may even loose prime unless the whole setup is lower than the level of fuel in the tank. As those air bubbles work their way back out of the system the ball is going to jump around.
Their new "flow through regulator" is actually a conical piston with holes. It is leaky by design, so it addresses #3 by loosing prime more easily, but repriming at starting up more easily (leaks in both directions.)
The only way to solve the issue is to feed the fass from a sump and then have the return go through the original draw straw, (not the filler neck) back to the bottom of the tank. Alternatively you could use a dual port sump and return to a sump. Or have everything go through straws. You just can't suction from the bottom of the tank and then return to the filler neck, up high. That way the loop won't loose prime when the truck is off. The whole problem with the system is a high return to the filler neck. Unfortunate but you have to be smarter than the marketing, which makes you smarter than their tech support too.
When you buy the thing, it's the greatest thing on earth with a lifetime warranty and priced accordingly. But when you discover the limitations of the system and you've already cut up your filler hose which is no longer made, you call them on the phone and they are a bunch of jackwads. "But muh bucket test."
So I have my fass plumbed into a 100 gallon fuel tank in the bed that gravity feeds to the fass. Here is a link to the video about my setup.
czcams.com/video/BUiWKP96g0A/video.htmlsi=oFKwN54daen7MWk8
I already have the flow thru regulator and I mainly have problems with fluctuating pressure when things are cold. 0⁰ F and colder. This is my second fass pump on this truck. The first one was flawless until the motor quit. This replacement one was good for about the first 50,000 miles until this started happening.
Moving forward I bought several electric heater to put into the tank and fass and might run coolant lines to the fass. I also bought the fass external regulator and want to try that out and see what happens.
@7 if your fass is mounted below the tank, you shouldn't have the loss of prime issues that I mentioned. That said, a bed mounted tank isn't the reality for most fass/airdog installers.
Lifting my bed to run a dedicated return hose from the fass to my spare draw straw solved the loss of prime when parked issue. I'm drawing from the bottom of the tank and returning to the bottom of the tank, so there's no way for air to enter the loop. The filler neck return is just not a good solution from a hydrodynamic design standpoint, but they do it for convenience. I'm betting 99% of fass customers have loss of prime due to drainback, don't know it, and are ignorantly happy. The truck still starts so you wouldn't ever notice it without a pressure gauge.
Also, I discovered my suction side filter (Donaldson P551001) is a great filter, but uses an internal standpipe on the clean side. This traps air in the filter, causing subsequent loss of prime issues. I modified my filter by drilling a small hole at the top of the standpipe. In the future, I'll adopt similar but non-standpipe models on the suction, water separator, coarse filtration side: Donaldson P550847 or P55800, Baldwin BF1212 or 1268, etc.
How are those bearins on that motor? Mine started leaking out the weep hole and pulled the motor apart and found the drive end bearing shot out and the shaft grooved where the oil seal rides.
I haven't checked the bearings but that would be good to look at
I am having the same issue right now on a 2nd gen dodge. Have you figured anything out?
I did ya, I got the issue solved now, I installed the fass flow thru regulator and my fuel pressure is nice and stable now. I'll upload a video about that soon as I can
@@tdm8817 nice! I called fass the other day and they told me that bending that spring is the best way to fix it and that it wouldn’t hurt anything to leave it like that. Actually the guy I talked to said his truck has been like that for 5 years
@@stevenrutherford3895 they told me the same thing, but when I tried that my pressure still was still fluctuating, tho not as bad.
@@tdm8817 I’m interested in how your regulator is set up. I’d like to did the same thing
@@stevenrutherford3895 I'll see if I can upload a video tonight about it
Fass has a few of there own videos about it but there not super helpful