Have a 95gpm FASS system and noticed the fuel pressure dropped from the normal 15 psi to about 8-10. A few days after noticing the drop I replaced both the filters on the FASS. Just after changing filters I noticed the press. up to 15 again. Later that day I went to take it out on the road... back to 9 psi? I was hoping it was just a tank of bad fuel clogging the filter. NOw I'm worried it may be more?
I always run plain ol' yellow, from the station, low sulf. diesel. Never ran any Biodiesel.

Any Ideas as to what's wrong? Any suggestions?

How low can you safely run the fuel pressure before the VP44 is in danger? I've already replaced that about 10K miles ago.

 

5 is my low point cut off for my truck for FP on my VP to where I would not drive the truck. Below 10 is cause for troubleshooting.

BUT for pressure issues, i ALWAYS ask if the gauge has been confirmed to be reading correctly. Especially if you have an isolator or electric gauge. These are the number one cause of pressure problems with the FASS.

Now just because you changed the filters don’t mean you still have a bad tank you are still running on. Remember, you have a strainer on the stock pick up in the tank if you are using it, so you might have debris on there if you did get a bad tank. Not that its very common, but I have seen it before.

Another test you can perform is the 5 gallon bucket test. Pull your suction line and return line off the filter neck. Place both into a 5 gallon bucket. Run the pump and truck off the fuel in the bucket. See what your pressure does. If it improves, you might need to inspect the tank.

See where that gets you and let me know....

 

My 95 did the same thing it started life at 16psi and slowly dropped from there when it finally got to where it ran around 8psi all of the time I put a new spring in it and I am up to normal again. The old spring seems to have lost some of its tension and had taken a visible "set" about 1/4" shorter than the new spring.

 

Guys, thanks.

Yep, I change all filters. Talked to Doug Conrad today and compressed the line coming off the front of the fass to see if pressure spiked...nothing. He also mentioned the 5 Gal. bucket test. I'll try that today.

Interstestingly, after playing with the above mentioned lines, I got in the truck to go to town and it was up to 15 PSI all the way. I even turned up the comp box and stepped on it and no change.. 15 PSI. Got back in the truck 60 min. later, fired her up and back to 8-10 PSI.

Why the pressure changes? I noticed the minute after I changed filters and bumped the starter a few times, the first start up I was up to 15 again. Shut her down and later the same thing...down to 8-10 max.

I'll keep working.

 

I still would like to see if we could confirm the gauge to be reading correctly...

Also....its the FASS return line you need to restrict to see if the pressure spikes.

Doug @ Advanced has always been very helpfull with these things....tell him i said "Hey" if you talk to him.

 

Did the 5 gal bucket test. I'd hit 12-13 every time (did it 6-8 times).

Hooked it back up to the fuel tank.... 10. This morning 5.

Fuel pressures are all over the place. Every time I start it up I get a different pressure. Heck, for a 15 min. ride to town yesterday I ran 15 psi all the way there, no changes or fluctuation. Shut her down and started up 20 min later and boom... 10 psi.

I'm thinking maby this is a sending unit problem, maby some junk in the tank?

Spoke with Doug (says hi) and his next advice is to verify the gauge, and check the tank.

Even with all the variations, truck runs normally.??????

 

Doug gave you good advice....that is where i would go as well.

Why do you think there are soo many issues with VP-44's? You cant feel low fuel pressure unless you run out of fuel. Hence why folks drive with low to no fuel pressure for weeks/months until they get injection pump issues. NOW with assuming the gauge is telling you the truth.....

 

should the pressure drop at all? i put a HPFP fass on a 98 with only an edge, pressure drops down to 9 psi at wot, idle 15

 

When my fuel pressures are running normally, the pressure never moves more than 0.5 even at WOT.


Diesel Dan.... Thanks. The more I think about this the more it seems like a tank problem. The 5 gal. bucket test, I think tells the story.

 

what could be my problem then? it dropped to 8 psi in the 06 truck in my sig, now on a 98 with way less power it does the same. why is that?

 

Could be a number of reasons. Have you check any of the suggestions i posted up above? That would be a good starting place.