justagoodolboy

I did just that, it runs like a TOP, but it empties the fuel can pretty quick because the return is going into the tank. I think I'll try running the return into the can to get a little longer run out of it because like I stated above if you do anything to let air in the line, like unhook the supply line or change the filter, it runs great for a while, sometimes as far as 20 miles, before the FP gauge starts bouncing and the truck loosing power. But its ALWAYS related to FP - steady gauge = smooth running truck with MAJOR power. Bouncing gauge = no power and odd engine noises, that I've equated to it just being nearly out of fuel.

Douglas2

hey-Hey!!!,
Seems to me you could just leave the cap off for a road test. I had a family member fill up the '91 and did not properly attach the cap and didn't find anything but a loose cap when it was time for more fuel. Should be an adequate vent, yes?
cheers,
Douglas

rcurrier44

They don't vent but they do have a one way check valve that allows air in. Just pop the thing appart and you can pull the valve rignt and still use the cap. Thats what I did when I was trying to figure out what is wrong with our fuel system.

kensmachine

Still would like to know what kind of fuel filter you are using

justagoodolboy

Ken, I'm using a Baldwin filter in the stock location, but the filter that won't fill up is one of those Fram inline fuel filters.

My first order of biz yesterday was to make sure I had a working vent. None of the items on top of the sender were vents. Bear - the picture you showed that indicated a vent was completely sealed up like it was molded that way. Since I had put in a new pickup tube, I had capped off the old supply line out of the top of the assembly, so I used that with about 3 feet of hose and a small filter on the end to vent the tank.

I then hooked the LP up to some clear vynl hose so I could see what was going on, and when I first cranked the engine, you could see the fuel rise out of the can, but it was not a constant pull on the fuel, it would move in the line, and stop, move and stop, never going backwards, but you could tell it was a pulsing type pull. Once it got to the LP, it was a solid stream of fuel, no bounce on the FP gauge, and it seemed to be idling nicely.

I then pinched the hose off just a little, and that's when the bubbles started. As the fuel passed through the pinch I created, it made about a foot worth of bubbles that didn't go towards the LP, they just stayed there, even after I let go of the line. I was thinking with the draw on the fuel it would suck them on into the LP and we'd be back to a solid stream of fuel, but that did not happen, so I killed the truck and drained the fuel back out of the line.

I hooked everything back up, started it again, same pulsing type pull on the fuel as it traveled to the LP, but this time I wanted to see if the LP could collapse the line, so I completely blocked off the line, and it indeed collapsed it no problem, but it also quickly started killing the motor.

My theory after finding no vent was MAYBE the LP was collapsing the hose, not completely, but restricting the fuel enough to affect supply, and even though I had tried loosening the cap while it was running, maybe the suction on the collapsed line was so strong allowing air into the tank didn't overcome it.

Now I'm just stumped! I am wondering with the pulsing fuel if the lobe on the cam is worn and not pushing the rob on the LP far enough in to get full travel, hence the pulse. I'm on my 3rd piston LP, and I just don't believe 3 in a row were bad.

rcurrier44

Rubber fuel line can de-laminate under a lot of vacuum and collapse the inside of the hose under vacuum. That's why they make negative pressure hose. I could also see it be very prone to de-laming if you used regular fuel hose in the tanks since the outside is not designed to be submerged and I know gas breaks down the fuel line fast..... not sure how bad diesel is. They make submersible fuel line for that.

rcurrier44

Oh and the bubles you are seeing are probubly cavatation (not from an air leak) witch are little gas pockets created by negative pressure.

kensmachine

what fram P/N are you using Ken

justagoodolboy

No clue - its the one hanging at Wally-World that has 3/8 inlet/outlet for a couple of bucks.

BearKiller

Those are just like the inline filters that I have been using for years.

They are wonderful little strainers that catch most of the gook that would otherwise clog a pump-screen or end up in the main filter.

I buy them at swap-meets in bulk for way less than one-at-a-time prices.




The problems you are describing read a lot like the situation I had some years ago, which led me to start using the inline filters.

My truck would start, run a second, then run out of fuel and die.

I almost never found the problem, which ended up being a big wad of gook lodged against the inlet screen of the piston-pump.

You already have an inline filter, so I doubt that your problem is the same.



TRY THIS:


BYPASS the lift-pump, letting the VE suck it's own fuel.

Under normal driving, you should not hardly be able to tell the difference.

If the engine runs fine with the lift-pump out of the loop, then you can get serious about measuring cam-lobe "lift" and such.

If it is a worn lobe ( which I highly doubt, but anything is possible ), then maybe you can replace the spacer with one not quite so thick, or remove it completely, thus giving the pump rod more "stroke".

TRENDZ

A few things come to mind as I read this.
You say you are an expert at dropping the tank. I suggest that you dont drop the tank. Get some buddys over there to help you lift off the bed. You may be pinching a line when reinstalling the tank. Having the bed off will help you easily diagnose any supply problems.
Another thing to watch for when adding a draw straw is the fact that the tank increases in size with a full tank of fuel compared to a lower fuel level. There is the possibility of the tank floor sealing off the inlet of the straw when your fuel level gets low and the tank shrinks. The shape of the tank also changes with the tightening of the tank support straps... another reason to remove the bed when setting up a new draw straw.

justagoodolboy

Good advice, and I did just that about 6 months ago - left the bed off for close to a month in between going from the factory bed to a flat bed, so I would have plenty of room to diagnose. No pinched lines or anything.

I all get what your saying about the tank stretching and moving, but that could be ruled out of the tank was full, as that would in my mind gurantee fuel around the straw to pull from. As far as it curling up or sliding over and sucking against anything, I have a 6 inch piece of steel holding it in place to keep in on the bottom and laying straight without any wrap.

I forgot to mention that when I ran it off the jug, it look only a couple of minutes for my truck to suck the 4 gallons dry, so that tells me the return line is in good shape at least!

After seeing the LP collapse the vynl hose, I'm wondering if that is not happening here, and that's where my restriction is. However, the pulsing of the fuel being pulled from the jug also concerns me, but I don't know if that's normal operation or not. The jug was on the ground and the hose ran over the fender, and when the fuel broke over the fender, it poured over and it took a minute or so to fill it up from the LP to the fender, but once full it was a solid stream of fuel.

kensmachine

First thing I would do is get rid for the 3/8 in line filter they where not designed for that much fuel flow or diesel. Diesel fuel systems return alot of fuel to the tank that is why the fuel filters are so big. A 400hp gas engine with a carburetor with a fuel system that has no fuel return can get by with a 3/8 in line filter. Not a diesel ! I am sure that your trouble is that you have to small of a filter. Ken

justagoodolboy

Ken, I was having trouble LONG before installing the inline filter, and took it off as soon as I saw it not filling up with fuel, and more importantly running almost dry. I posted about it in hopes it might shed some light on the other problem that's obviously kicking my tail.

BearKiller

I have to dis-agree on this one.

The reason to run the inline filter is NOT as a main fuel-filter, but as a STRAINER to catch the stuff that would otherwise clog the inlet screen on the lift-pump.

Like I have already stated many times, I have been running them for several years with no fuel system issues whatsoever.


They use the same filters as the ONLY filter on big V-8 double-pumper gas-burners that are eating five times the fuel that we burn.