My FASS has developed a problem of erratic fuel pressure. Since it was new it would make 21 psi at idle, 18 at WOT. Now it sometimes is 15, sometimes 11, sometimes 5 or less. The pump does not sound "normal", and if you open the fuel filler cap while it's running you can hear the pump pushing fuel back through the return, almost like it is bypassing fuel (do the FASS systems have a bypass?). I started it one time yesterday and the pump did not come on, checked relays and grounds all are okay. This is the only time the pump has not started.

The FASS is a 150/95 full system w/filter and seperator. It is about a year and a half old, maybe 25,000 miles, filter/seperator have about 2,000 miles on them.

Any input would be greatly appreciated.

BTW, this is by no means meant to belittle the FASS system or DPP, I love the pump and it has been very reliable till now. I fully understand that part failure is part of playing the game. I would just like to get this figured out so I can drive my truck again.

Thanks

 

i had erratic fuel pressure last night and the truck stalled on me once even...played heck getting it started again, then realized "hey dummy, put some fuel in the truck so its not sucking air"

I can't believe I let it get that low...I am good about keeping it above 1/4 tank in the winter.

 

Ernie, that's the same FASS I have...the 150/95-1008 model. So far it's been consistant, but it only reads 13.5 idle and drops to 12.5 while driving under normal hwy and city conditions. It's not been erratic though....just remained consistant.

TJ...is there danger in letting the tank go as low as when the little fuel low indicator light comes on the dash ussually just after the last hash mark on the fuel level gauge?...if our trucks have a 35 gallon tank...even letting it go to the low fuel warning light I've still only ever put like 27 or 28 gallons in to fill it...so I'm guessing logically with 6-7 gallons in the tank at the last 1/8th tank hash mark still we should be safe, correct?

 

my stock fuel level gauge doesnt work, i have an autometer gauge wired up that reads pretty close, but when it gets down close to 1/8th tank its off by a little, add in that i have a draw straw which sit above the bottom of the tank, and when i get low, every time i hit the brakes and slosh the fuel around it starts sucking air.

 

I would check your brushes to see if they are worn or corroded. My FASS quit a few days ago and it turned out to be the brushes.

Good Luck

 

I have the same thing with my draw straw. When the tank gets to just about 1/4 tank, I can make the fuel pressure drop to 0psi with a hard stop or start...I need to be more conscious of the fuel level and fill it up when it gets low.
Just thinking about it now, this cant be good for the lp's and probably helps to kill them early....

 

I am fighting this now. Without a FP gauge I would have never noticed it. I am wondering if my stock fuel sender unit in the tank has a hole/crack that below about 1/4 tank it starts to pull air and I loose FP. Could be why I am on VP #6. Historically, I would run a full tank down to when the light comes on (about 8-10 gals on my truck) before refill.

Sorry to get off topic Ernie, I have read the brushes do require replacement but have no first hand experience with the FASS.

 

Erratic fuel pressure is very strange on the FASS....and normally what we see cause it is lack of fuel (Or restriction) to the inlet side of the pump. The second more common thing we see is gauge error.

I would start by confirming your gauge is reading correctly. If its electric, double check with a known working mechanical. I have seen electric gauges on VP-44 engine do exactly what you are describing. VP-44's and electric sending units mix like oil and water.

If you have an isolator, by pass the isolator with a gauge to confirm pressure. If all is good, go on.

Find a clean 5 gallon bucket, or something you can fill up with some diesel. Pull the return line of the FASS off the fill neck for the tank. Turn the pump on by bumping the engine. Allow the pump to fill up the bucket for about a min or two. Then shut the pump off and place the suction line in the bucket. Run the pump and see what your pressure does. If the pump sounds quiet and pressure is solid, I would check your suction line and in-tank sending unit. To empty the bucket....just reinstall the return line to the filler neck and run the pump until the bucket is empty.

BUT if the pump is not running at all now, check all your connections. Fuse, relay and such. If you bump the engine, the pump should run for about 20 seconds.

If any of these things dont help...contact your FASS dealer with your serial number and have them call me for some more options.

AND yes, we have seen stock sending units crack and suck air at a certain point…its rare…but has been found. (To the Geis,…im willing to bet you have not found your problem that is knocking out your pump….that is mighty bad string of bad luck there!)

 

Thanks Dan, will try the bucket this weekend when it warms up a bit. I need to get a mechanical gauge on there to bypass my pillar gauge and see what it reads. The pump just sounds strange like it is working really hard, I was leaning towards a problem in the tank or with the inlet side of the pump.

Dan, I tried contacting my dealer, got voicemail, and no call back yet. Not really worried about it though I know they are always swamped with work.

 

Ernie...
IF you still have the schrader valve in your system somewhere I have one of the defunct "Black Mountain Diesel" shops built mechanical test gauges you can use.Its a really nice unit and I have had it for years and used it once,LOL.

Sounds Like Ladell,LOL.If it is I was up there on Wednesday and they are running around in circles.He told me that they are booked up with work until Mid February already.

If you need some help let me know I will gladly give you a hand.......Andy

 

No, Andy there is not a stock fuel line on the truck so no schrader valve. I have a mech. gauge laying around somewhere, I just need to find it. My pillar gauge is mech. too, but with an isolater. I don't think it a bad reading though because my low pressure LED comes on when the gauge drops below 6 psi, just like it is supposed to, and the sender for the LED is on the FASS pump. I'll get it figured out this weekend, worst case I'll have to throw my spare FASS 95 on there until I get this one figured out.

It's not Ladell, bought it from a place down here in MD.

 

Check that isolator irregardless.....never make any assumptions when it comes to those....(Had two today that this was the issue).

Rebleed it on the diesel side and make sure the coolant side is bleed out as well.

If you got a spare....might as well check it out...and send the other into me and ill run it on our bench here......

 

Isn't there a CAUTION in the owner's manual about running the fuel level down below 1/4 tank, esp constantly running it down to the Low Fuel indicator?

 

Its been a while since i have read any of the manual, to be honest. BUT if there isn't, i will make a note to bring this to Brad's attention. I'm going right now to pull one.....

 

I tried the filling a bucket, and running the pump from that, virtually no pressure change, 1-2psi at most. Mechanical gauge t'ed into supply line at VP shows the same pressure.
I pulled my 150 off, and put my 95 on and the 95 just blows the fuse, doesn't even try to turn the pump, turn the key and the fuse pops instantly.
Any other suggestions for things I can try at home, Dan, or should I just ship them both to you and let you check them out?