I cannot figure out what's going on. The truck has been running great. It has a FASS 150 that always runs at 25psi cruising, and around 21psi WOT.

Saturday, I replaced a tranny cooler that was leaking. After I finished, I took the truck out to make sure nothing was leaking. While I was cruising on the freeway, I noticed that the fuel pressure gauge was reading 0psi. I tapped the gauge, but it stayed on 0. The truck was running fine though. I even shifted into nuetral on the freeway and turned the key off, then restarted it. Everything was fine, so I figured it was the gauge. When I got home, I swapped another gauge. As soon as I cracked the fitting, I must have lost prime and the truck would not restart. I then started checking the FASS. With the key on, I did not get anything, but after cranking once (The test light flickered while cranking), the test light would stay lit for about 45 seconds, but no sound from the FASS.

I figured that the FASS must be bad, so today I removed it. Just to be sure, I connected the FASS directly to the battery. It ran fine. I then checked the ground and hot at the frame rail, and got the same results as Saturday. The light would flicker while cranking, then stay solid for around 45 seconds. I decided to reinstall the FASS. After connecting the hoses, power and adding a new filters, I cranked and heard the FASS buzzing. Cool I think, so it buzzes for 45 seconds, then stops, and no movement in the fuel pressures gauge. I figure that it needs to prime the filters, so I do it a few more times. After the 4th time, the FASS will not buzz anymore.

I check the relay, and even swap a new relay in, but nothing. Then I removed the relay and ran power from the battery to the output of the relay. The FASS starts buzzing and I can heard it change pitch, like the filters are filling. I look at the gauge, and the needle is at 5psi. I let it run like this for probably 10 minutes, but no movement on the gauge. I then open the water drain, and fuel comes out. Then I spin the front filter off and it's only about 3/4 full. I decided to fill it from from a can, and put it back on. I put the wire back on the battery, but the gauge still doesn't move.

I cranked a few times thinking that the injection pump was probably dry, but still no movement. Finally, I cracked the fitting to the gauge to bleed off any air. As soon as I crack the fitting, fuel starts coming out. I let it run like this for a bit, and finally I hear the FASS change pitch. I tighten the fitting, and crank again. As I crank, the pressure dropped back to 0 again. I repeated this process 3 more times, and each time the gauge went back to 0. I couldn't get the truck to fire.

What am I doing wrong?

Is the FASS really bad, and just won't build pressure?

What else would cause this?

I checked the relay wiring, and tested the ground, battery feed and switch input. The switch and ground plug into a connector on the harness.

Thanks in advance for any help. I need to get the truck back up and running.

Sean

 

Has the pressure regulating valve in the return line of the VP44 ever been changed? It's set to open at 18psi. If you have 25psi, it is probably wide open. It may have gotten stuck open from this, and is constantly allowing fuel to dump right back to tank. For the price of the valve, $25 or so, I'd give it a shot.

 

Thanks. I'll call the dealer this today. Is it a standard part?


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It's pretty standard, I wouldn't call a dealership though. Their price will be high. If there is a local diesel shop, try them. Otherwise:
BOSCH VP44 FUEL OVERFLOW VALVE (98.5-02, 24V)-Geno's Garage
Overflow Valve Cummins 24v 98.5-02


I also stumbled across this:
VP44 Overflow Valve

 

I did some more trouble shooting today. I installed a gauge in the filter head of the FASS and the gauge didn't move. I then pinched off the return line from the FASS and the gauge still didn't move. Finally, I pinched off the output line from the FASS and still nothing. At this point, I've pretty much determined that the FASS is bad.

 

When you crimped the line did you bump your starter to let the FASS run for a long period of time? What is the make and year of your truck? Can you tell me which FASS system you have?

 

OK SO HERE IS MY PICKLE I STARTED LOOSING FUEL PRESSURE LAST WEEK SINCE THEN THE TRUCK HAS BEEN IN THE GARAGE AFTER LIFTING THE BED AND REMOVING THE SENDING UNIT WHICH IN TURN HAS A PUMP ON IT I HAVE FIGURED OUT THAT IT HAS WENT OUT REASONING BEHIND THIS I HAVE SINCE DISCONNECTED THE FUEL IN FROM TANK TO FASS 150 HD AND PERFORMED A 5 GALLON TEST NO FUEL COMES SQUIRTING OUT OF THE FITTING I DISCONNECTED THE FUEL LINE FROM I CAN PRIME THE FASS AND I KNOW FUEL IS GETTING TO THE INJECTORS DUE TO ME HAVING TO CRACK THEM TO REPRIME AFTER RUNNING OUT OF FUEL TWICE AND BY THAT I HAVE FIGURED OUT THAT MY PUMP IS NOT COMING ON DURING RUNNING I READ NO PRESSURE NOW BUT AT THE START OF THIS PROJECT I COULD GET MORE THEN 6 AT IDLE AND WOT ANY ADVICE WOULD BE GRATEFUL SEEING AS THOUGHT I HAVE DEP'T WITH THIS FOR TWO LONG AND IM SICK OF SMELLING LIKE FUEL

 

So your FASS system is hooked up to the in-tank sending unit?