Now I love my FASS, and have had good service out of it, but I suspect it has problems and I am eager to figure out how to troubleshoot the problem and get it fixed.
The problem is the FASS loses prime when the truck sits for a while. Overnight the prime loss isn't too bad, and a couple of cycles of the key will get it back. After a couple of days though, it takes forever to get the prime back.
When I installed the FASS kit 2 years ago I found the quick connect that goes to the fuel tank was a piece of junk, so that connection got clamped. I am using the non-clamping barbed fittings elsewhere. At first it was all good.
Once, probably 6 months or more, back, I had the FASS leak like crazy on a 100 mile trip. I couldn't tell where it was coiming from so I just kept driving. When I got home though, and looked for a leak, it had stopped leaking and has not leaked since.
I just changed the fuel filter and water separator on it and that seemed to change the behavior a little, in that the prime doesn't seem to go away as quickly, but over a few days, it will still bad about losing prime.

Any ideas on this, and how to test to make sure of the problem will be appreciated.

Thanks,
Chris

 

My guess would be a small leak that's allowing air to enter the system. Not too sure how you'd detect it though. I might start with checking the fitting at the Injection pump and on the pump itself. Maybe even replace the fuel lines. Can't be too expensive I wouldn't think.

Doug

 

HUM....i agree. Make sure you have thread sealant on all of the pipe fittings. ALSO....there is a 3/4" or 5/8" check ball under the T-block (Up-side down "T" bolted to the base plate. Motor and pump attach to it.). If a piece of trash get stuck in the ball seat.....this might cause a loss of prime, or hard prime situation. You can check this with the system in the truck. Get a 7/16"/11mm gear wrench or standard wrench (just LOTS easier with a Gear Wrench) and take the 4 vertical bolt holding the T-Block to the Main Base. You should haver 3 short and 1 long with a nut. ALSO if you unit is older, you will have the motor clamp that holds a tang that bolts to the Pressure manifold. Just undo the 2 bolts going into the pressure manifold. Pull the T-block and motor off the system. You should be able to see the ball sitting in its seat in the main base. Check for Debris and size of the ball. If its 3/4".....we have a new 5/8" ball that is better about priming and such. Also check the condition of the O-Rings. In most cases, you can reuse the rings....but we have tons here you can get comming you way to replace them. Contact you dealer with these part numbers:

OR-017 (O Ring)
OR-030 (O Ring)
1901-625-5939 (5/8" ball)

Might have a cracked pickup tube in the tank as well. We have seen this as well. Hope these suggestions help.......

 

Go figure. I started the truck yesterday, after sitting for a solid 2 weeks and the FASS was at 15 pis immediately and never let up. The truck still didn't want to start, as is normal when it loses prime, but the pressure was there from the moment the key turned on. Usually it jumps up to 15 psi immediately then drops to 0 for a while, until I cycle the key and turn it over enough that it picks the fuel back up.
This time it was more like the prime had been lost downstream from the FASS, before the VP44, because I had to turn it over a while, even though I had fuel pressure, before it started. Once it has been running a minute it will restart with a bump of the starter.
I'm just unsure of a good way to check for a "vacuum" leak on a line without having a transparent line.

I am not sure how much this huge 1/2 fuel line costs, but I bet it ain't cheap.
Anyone know of a 1/2 inch fuel line that is BD compatible? I don't know if my current line is or not.

Thanks,
Chris

 

My sugesstion is either open up the line to the FASS or pressurize the supply line to the FASS with an in tank pump.This way you are not pulling a strong vacuum on the suction line,which tends to pull air espesially on high demand situations.

 

Are you familiar with the ECM operates the lift pump under starting situations?

When you turn the key to run, after the truck has been sitting, it will bump the lift pump (or FASS) for about half a second. The pressure will spike and then fall off. Then if you bump the engine, it will run for 20 seconds or so and then shut off. When you try to start the engine, it will pulse the single wire to reduce the duty cycle of the pump (To lower the pressure while cranking).

I’m not sure if you are confusing the normal operation of the LP cycle or not here. Correct me if im wrong, but what you described above sounds normal to me.....except the no starting.

Our lines are Synt. rubber....i have never personally had an issue with BD in my truck....and others are running it with no issue. The fuel line used in early 90's trucks were the ones to watch out for.

The FASS uses 3/8" line.....

Also make sure you have the second O-ring on the water sep. nipple. It uses the ring built onto the filter and a second one that slides over the nipple. It is very important that the water sep. has no leaks...its on the suction side of the pump.

 

i been running biodiesel for the last 2 years and none of the fuel hose that came with the kit has been damaged.

 

Good to hear about the fuel lines and BD. I have already eaten up 2 of the "farm" hoses that came with my Fill-Rite pumps. I'm now going to Goodyear hose that is specifically BD rated. I have just been unable to find a BD rating for the Goodyear hose that came with the FASS, and worry it might be slowly falling apart inside.

As far as the FASS behavior, I am well versed in the ECM operation of the lift pump. When the problem is occurring the pressure come up for a second, then drops, even though the pump is sitll running. This is when the key is turned on. Then I bump the starter and just stand there listening to the pump try to prime itself. The tone changes when the fuel pressure come up.
I am still suspecting a leak, but not sure where. I can test a little right now, but cannot start the truck at this time as I have a turbo off, being repaired.

Thanks,
Chris

 

overflow valve in pump return line draining fuel out of pump ????

 

Dunno. I'll have to look. I think the return goes into the filler neck return hose higher than the pump, but I am not absolutely certain of that.

I am now having thoughts of temporarily replacing pieces of hose, one at a time, with clear plastic hose, so I can see what's going on, and either find the pump problem or eliminate the pump as a suspect.

Chris

 

Chris,

Have you tried the 5 gallon bucket test in my trouble shooting manual? I am leaning tward your stock sending unit might be causing fits. Double check you gauge operation with another gauge.

 

Gee, I was unaware of your troubleshooting manual. Where can I get that to read? Is it online?
I have an Autometer mechanical FP gauge, with isolator, so no sending unit to fail.

Thanks,
Chris

 

Go up to my first post and look in my sig..........i got a link to it there.....check the isolator closely. Rebleed everything. Make sure you got sealant on all pipe threads.....we see a lot of thoes cause issue. New and old. Try to temporarly by-pass the isolator. See if your pressure does the same thing. Just giving you some things to look at and try......

 

Thanks for the info, Diesel Dan. I will try some of these things as soon as I can.

Thanks,
Chris

 

Dan,
OK, got my suction line in a bucket of biodiesel. The pressure comes up to 3-4 PSI and stays there until the engine is actually running, then after running for a few seconds the pressure pegs my 15psi guage. Pressure is measured with a mech guage, 18" from the VP-44 inlet. When I cut it off it loses prime immediately, and turning the key back on and bumping it immediately after shutting down, I get the 3-4 psi again and it stays that way, no matter how many times I bump it, until the engine has been started again.
I clamped the fuel line 4 inches from the VP44 inlet and this does not change the behavior.

Please advise,
Chris