What causes low fuel pressure?

[clinker clint]

Hey guys, My 93 W250 has a fuel pressure gauge, after filter. When I first got the truck, it would cary about 5lbs of pressure at idle. It started dropping down to almost nothing anytime I gave it any fuel at all.
I changed fuel filter, lift pump (twice), pulled the tank and pickup (tank and screen were clean) then I found all those stupid o-rings in the fuel lines. I replaced all those dang o-rings and finally, thought I had the problem fixed. Truck has been pushing about 6lbs of pressure at idle and 5lbs cruising down the road. Mash on the throttle and I can get it down to 0lbs.
Everything has been good for about a year. A couple of days ago, I let the truck warm up in the barn and it died while idling. I thought the fuel had gelled up, even though I had treated the fuel.
I put diesel 911 and fresh fuel in the filter and it fired up. only ran about a min and it died again. I put my spare filter in and now the truck runs. At idle, the turck carries 5lbs of pressure. If i bring the RPM up to 1500, it falls down to 0psi.
I have bled the system several times and even blew air back through the suction line, thinking maybe, just maybe there was an obstruction in the tank/screen.
I also treated the tank with whatever is in the white bottles (diesel 911 stuff, just white bottle) and also Howes treatment.

So now I'm ready to drop back and punt. I want to fix this thing, once and for all.
So I'm looking at this kit:
http://www.thehungrydiesel.com/Low-Pres ... t-Pump.htm
The problem is I still think I'm getting air in the lines or maybe there is an obstruction in the lines somewhere?? This makes me want to replace the fuel lines. As I'm sure you know, the fitting that hooks to the sump is just like the fitting on the lift pump, smooth metal that requires those stupid fittings with the o-rings. I want that all gone. So I found this:
http://www.thehungrydiesel.com/Diesel-F ... P-SUMP.htm
Is this a good option? It says nothing about having a pickup installed. Anything more cost effective? I don't need billit anything. I just want it to work.
I could do a draw straw:
http://www.thehungrydiesel.com/Dodge-Ra ... II-DS2.htm
Thing is I have read that you can't let your fuel level drop below a quarter tank. I don't like this. I use this truck. I haul with this truck. I fix fences, drive on steep slopes and do all the things you normaly do with a farm truck. Picking up air seems like a real issue with this design.

Is there anything I'm missing? Is there anything else I should be looking at that would cause my low fuel pressure?

Any other products I should be aware of that could solve this issue?

Mods to the turck:
Pump turned up a quarter turn before runaway
Smoke screw and star spun in quite a lot
ground fuel pin
4" straight exhaust
3200 spring
gauges

Thanks a lot for any input.

[clinker clint]

Last night, I left the truck in a heated building for 10 hours. I wanted to see if the fuel pressure would get any better if the fuel was thinner from being warm. Made no difference. May be worse. This morning when I shut the truck off, I was only carrying 1.5lbs at idle.

I figured that less fuel would = less boost so I tried a copule of WOT pulls just to see what it would do. Still produces 28lbs of boost. I assume this to be a normal number. It's. The most this truck ever builds. So this tells me that the VE isn't starved for fuel. I know doing this isn't good on the pump, I just wanted to see if there was a measurable diference.

[ellis93]

Honestly....go ahead and do the piston pump upgrade and be done with it. It's the best you could ask for in mechanical supply pumps but I'd make double sure you suck no trash thru it. If the bore is scored the piston won't seal off and pressure will suffer.
I put a strainer in my supply line to see if there's anything getting past the factory sock in the tank. Peace of mind.

[CumminsPower59]

First of all, the lift pump upgrade is always a good choice.

The quick connect couplers on the fuel lines are a moot point, when you replace your fuel lines, the new line will slip right over the nub on the sending unit and when you get that new lift pump, get the appropriate sized hose barb. No more O-rings. I bought a 50ft spool of 3/8" I.d. marine, biodiesel comparable hose and replaced both lines, feed and return. Make sure to use a in-line canister style strainer to keep the big crap out of the new lift pump.

If you still are having flow issues, maybe the pickup in the tank may have some junk stuck to the strainer...

[RCCUMMINS89]

Sounds to me like your in tank pick up is getting clogged up.


We also offer a "duel fueler" sump. You can either draw twice out of it..... or plumb your supply in one side and your return in the other, completely by passing the top of the tank stuff. That runs $140.

[clinker clint]

Sounds to me like your in tank pick up is getting clogged up.


We also offer a "duel fueler" sump. You can either draw twice out of it..... or plumb your supply in one side and your return in the other, completely by passing the top of the tank stuff. That runs $140.

Can you post a link to the duel fueler sump? I searched the site and I didn't find it.


Thanks so much for everyone's input. I picked up another stock pump today because I need to have this truck running right now. It's my daily driver till I get my little work car back together. I'll get the piston pump ordered as soon as I figure out what else I need to pick up at the same time.

Thanks again!

[clinker clint]

Well, as my truck is my daily driver for now, I had to do something. I picked up another pump and a spool of 50psi 3/8" fuel vapor line. The counter guy looked it up and said it was rated for diesel fuel. I was not familiar with "fuel vapor line" so if that's an issue, let me know.
Anyway new pump, new 3/8" line. I dropped the tank again and checked screens and everything was clean. Fired the truck up and it went to 10lbs. Went for a test drive and I could not pull the gauge down below 5lbs.

After a day of driving I am now down to 6-7lbs at idle and 4lbs WOT. Not sure why that has changed. Hopefuly it will level off there.

I'm still planning on putting a piston pump in but this will get me by till I decide what parts I need.

Questions: What is the point of replacing the return line unless it is leaking?
Is 28lbs of boost normal for these motors on stock turbo? It sounds like I have a boost leak coming from around the turbo but could be just the sound of the turbo itself.

Thanks again.
Clint

[RCCUMMINS89]

To make sure there is no issues, as far as blockage, in the return line as well (point in replacing both). Also if you are upgrading lift pumps, the return also has to return more fuel. Not that it is an issue with the piston lift pumps (more of a mechanical thing, where they by pass nearly all of the fuel at an idle).

I'm wondering if you are literally just getting junk chinese lift pumps that keep going bad.

28psi.....depends on mods to the truck. That's way higher than a stock set up will do. But with pump tuning, sounds about normal.

[clinker clint]

Well, I've got a feeling we are on the down hill slide. The truck is now carrying 5-6lbs of pressure at idle. WOT is down to .5-1lb. I will continue to monitor it and see what changes.

Yes, I am getting cheap Chinese pumps from Napa. Which is sad. It used to be, you went to napa, paid a little more and got a better part. Not so anymore. I stopped by Advance Auto a while back just to look at one of their pumps... same dang pump. This is the third pump I've put on this truck in 2.5 years.

Thanks for the explanation on the return line. I did not replace the return yet but I will when I put on the piston pump.

RCCUMMINS89, can you please post a link to your duel fueler sump?

[RCCUMMINS89]

http://www.thehungrydiesel.com/TRP-Dual ... fueler.htm

[clinker clint]

Great, thanks for the link.

I've got some quesions. The sump on my truck has several things going on.. There is an electrical plug for the gauge. There is some sort of vent (not hooked up to anything). There is a blank port/boss. Then there is the inlet/outlet and maybe another vent? I'm not sure what the vent is but it's an open 3/8ths hard plastic tube much like the fuel ports but pointing vertical, not horizontal. Nothing is hooked up to it. (There are lots of things that aren't right about this truck that I am slowly trying to get lined out.)
There is also the screens, gauge assembly, baffle etc all down below.

The dual fueler sump does not seem to have any type of draw tubes. At least not pictured. Are they included? Is this meant to be a direct replacement to the factory sump?? If so, am I now going to be running without a fuel gauge?
Maybe this is something that requires a new hole cut into the tank?
Thanks for the help.

Truck is still maintaining good fuel pressure.

[AHineman]

The new sump goes on the bottom of the tank.

[PToombs]

The vertical opening is for a gasser application. If you put something in it you will see it's not drilled all the way thru. I actually drilled it and use it to pump fuel from my rear tank to the front.

You need to drill a hole in the bottom of the tank and put the sump in.I put mine towards the rear. I drill the big hole, then I hold the sump up and drill 2 screw holes across from each other. I then put in the screws to hold the sump from moving and drill the rest of the holes. Get 4 screws with the same thread and cut the heads off to make studs, put in the plates and install the studs, 2 in each plate. Put the sump on and put screws in the open holes. Remove the studs and put in the last 4 screws and tighten. That's the short version, usually you have to put on sealer, install you fittings, etc.

I see you have the tank out, that makes it really easy!

[clinker clint]

The vertical opening is for a gasser application. If you put something in it you will see it's not drilled all the way thru. I actually drilled it and use it to pump fuel from my rear tank to the front.

You need to drill a hole in the bottom of the tank and put the sump in.I put mine towards the rear. I drill the big hole, then I hold the sump up and drill 2 screw holes across from each other. I then put in the screws to hold the sump from moving and drill the rest of the holes. Get 4 screws with the same thread and cut the heads off to make studs, put in the plates and install the studs, 2 in each plate. Put the sump on and put screws in the open holes. Remove the studs and put in the last 4 screws and tighten. That's the short version, usually you have to put on sealer, install you fittings, etc.

I see you have the tank out, that makes it really easy!

Great! Thanks for the information! Ten four on drilling the big hole in the bottom of the tank.

[clinker clint]

Well, I'm still running the napa pump and new line for now, probably for another month or two. It's been working fairly well. When it's cold out and after a cold start, the pump is pushing about 8lbs of pressure.

Most days this winter after the truck is warmed up, it's carrying about 6lbs at idle and 4.5 running 60mph down the road. I can't pull it down to 0 at WOT... untill yesterday.

One thing I had forgotten to mention earlier is for as long as I have owned my this truck, if you leave it out in the sunlight, parked, my fuel pressure will suffer. Park it in the shade and there won't be an issue. I'm not sure at what temp this starts happening but it happened yesterday for the first time in a long time. It got up to about 60*F here yesterday and the truck was parked out in the sun. Even if it's 100* out, if the truck is parked in the shade, fuel pressure will be fine. Park it in the sun and fuel pressure will be low. Yesterday, at idle it was about 3lbs. Running down the road, it dropped to about 1lb. Floor it and it will go down to 0.

Anyone else ever see this?

I do believe I need to replace my pump with a piston pump and get the bottom pick up sump. I realize this and believe it should fix my issues (I hope). I'm just curious if anyone has ever experienced these symptoms in the past. I'm hoping I don't have another issue I'm not aware of.

Thanks again,
Clint