Haulin_in_Dixie

Since making the change to bottom feed on my truck, I believe that the fuel feed on the ISB is a very ignored item. To start with the engine was designed with a bottom feed system in mind and Dodge modified this for the plastic tanks that already had a pickup assembly for the gas engine. Cummins mid sized trucks do not use the tank system of the Dodge. They do share the same fuel filter and lift pump design.

The stock second gen fuel pickup is a complicated deal. I would guess that they set it up the way they did to prevent fuel starvation at low fuel levels. What the designers have ended up with is a small tank within the tank which is about 3 1.2 inches in diameter. It has both the fuel pickup and the return in the same chamber. My first thought after examining the system is that the fuel must get quite hot on a summer day, constantly recirculating the same fuel through the VP44 and no fresh fuel added unless it is needed to keep the chamber filled.

I examined my pickup system and found no problems with it except that it was inadequate to supply enough fuel to the system. I found no leaks although I had an air pickup problem for a long time. By eliminating the fuel pickup from this chamber and drawing it from a bottom feed the results are dramatic. The fuel pressure is constant and steady, immediately snapping to full pressure as soon as the key is turned on. No more 4 or 5 pounds and slowly climbing to 15. The overall pressure went up a pound or two. The gage has always vibrated with the pounding that the VP44 gives it unless I trapped air in the gage feed line. Now with the bottom feed and the gage line bleed of air the gage action is steady and solid. Is the cause of the vibrating gage due to air in the system behind the gage and the vp44 vibrating against this cushion?

Although I cannot explain the difference, the engine did not feel rough or not properly running, but with the change of the pickup it has a new smooth feel that is always with it and a deep purr of the exhaust in the background. The VP44 is returning much more fuel as in the picture. This should translate to a better operating VP44. The mileage is up a bit, not a lot, but noticeable.

I may be wrong, and the experts should get in here and add their comments, but I think the pickup system is very overlooked and is as important as the larger lines and lift pump changes. I am betting that this is the root problem with the fuel system on these trucks, especially as soon as any fuel related mods are made. I do not think that a bottom feed is necessary, but a free pulling pickup needs to be added that does not rely on the float chamber for its fuel. This would be an easy mod, just a piece of line added in place of the coiled line in the chamber and getting to the bottom of the tank. With the FASS system, which incorporates a pre filter before the pump, there is no need for screens or other obstructions in the system.

I was impressed that there was no trace of water in the tank or any other sediment after over 260,000 miles on the truck. This change of the fuel pickup has been the most noticeable improvement to the fuel system that I have made. My engine now has adequate fuel supply for the first time.

Smokee

Good analysis, Haulin. Sure makes sense to me!

MDW

Here's what I did.



I cut the bottom off the stock pickup and removed the one way valve, the black thing in my hand. I reinstalled the red screen.
Its free flowing now

infidel

All I can add is that I know a couple guys who started feeding their 24 valve fuel from the bottom of an in-bed tank. Both still had their stock lift pumps go bad.

According to laws of physics when sucking fuel from the bottom of the tank it should make no difference in flow if the fuel comes out the top or bottom of the tank as long as line sizes are the same.

BigBlue

I don't think haulin did this to make the lift pump last longer (he doesn't even have a lift pump), I believe the reason he did this was to stop the air from getting in the lines and allow the pump to be able to draw in some fresh, cool fuel instead of hot, recirculated fuel. That would make the work on the pump a lot easier.

If I'm reading this right, you basically just went and removed all the stock pick up stuff, and put a line that lays on the bottom of the tank for a return, and then sealed it all off. Am I correct?

Haulin_in_Dixie

I said in the post that it would work just as well that way, but I put a bulkhead fitting through the bottom of the tank for the feed. In my pictures I have a shot of it. I braised a big washer to the head of a bulkhead fitting, drilled a 3/4 inch hole in the bottom of the tank and hooked up. Sure will be easier draining the tank next time The difference is amazing, with no air being picked up. The problem is that the chamber that houses the pickup and return cannot replenish the fuel fast enough to pull clear fuel. The next post gave a good method of accomplishing the same thing, just get rid of the rubber valve and float for it. In my case I did not like the whole concept so did away with it.

CTD2500

When I re-engineered my fuel system...I removed the OEM filter and installed twin Stanadyne FM100's...a pre 30micron and a final 5 micron. The lift pump also went between them down on the frame. I gutted the fine mesh fabric of the pickup point, installed all 3/8" fuel lines with straight fittings and now see pressures between 14 and 15 at all times even under hard pulls. If it does dip down into the 13's...it rebounds quickly and usually goes higher than 15. This is under hard acceleration and usually in third gear.

Note that the module container serves to keep the pickup tube submersed in fuel when your so low the fuel runs away from the pickup for a second. However...that is almost impossible to do unless your at 1/16th tank and on a 45 degree incline.

Gutting the module is good...but always install a filter prior to the lift pump.

As to the bottom feed...I didn't do it cause I'm running a 2WD. Too low. But the lift pump should have no trouble pulling out of the top once prime is established. We have a F650 at work that suffered a VP and lift pump failure. It is top feed outta the tank...but it would make no difference if it were bottom feed as the entire tank is lower than the lift pump so one way or another it has to lift fuel a certain height no matter the outlet of the tank.

Nice work.