O_key_doe_key
I apologize for not getting back sooner, but I had a painting project that I needed to finish so that took priority
Before I start one thing that I believe is different, but I have never dropped my tank and looked inside and base this on what other Vanners have found. The tanks on the E-series are metal and there is a slush box type affair around the pickup. It is IIRC about 10in or so square and around 3 or 4 inches high, open on the top and with slots around the bottom. This provides somewhat of a sump so under low fuel conditions the fuel slosh is somewhat restricted. Also, the E-series even has an extra "quick disconnect" between the tank
HERE and the fuel pump.
My first thought is if it's not really broke don't try and fix it. I'll give you the "punch lines" and then go into details as the need arises ....
1. IMHO there is nothing seriously wrong with a properly functioning pre pump fuel system except that I would still recommend running a 3/8" fuel line from the top of the tank to the fuel pump and as Haul_n has done ream out that fitting on top of the tank. I did not find any air problems with at least the quick disconnect on top of the tank, but eliminating these QDs, especially the one on that vibrating pump just makes good sense. In my testing even when I introduced air into the stock fuel system before the pump even to the point that it got back thru the mixing chamber and I could see free air coming from the mixing chamber and going into the fuel pump I never noticed any effect on engine noise or performance. I know and believe based on the air problems that Haul_n worked on if air does get to the engine it will cause the engine to be noisy. I could never positively confirm where this air went, but I'm fairly confident it did not go thru my injectors.
2. The pre pump filtering and the stock filter's attempt at removing water post pump that most likely contains only "emulsified water" is not good enough IMHO and might be even characterized as pathetic at best. However, by simply installing a Dahl or Racor Turbine type pre pump filter with at least a 10 micron element will improve things by probably an order of magnitude and is a great way to monitor potential air issues between the filter and the in tank pick up system. This is only a like a $120 mod and just like adding a coolant filter just makes sense. Also, the Dahl filter will go mucho miles and should really eliminate or greatly reduce the frequency of changing the in valley filter and draining the factory fuel bowl. I can't put real numbers on this, but now I never drain my factory fuel bowl and plan on running my Dahl filter for at least 40-50K miles between changes and probably going that long for the factory filter. If you see "bubbles" coming out from the difuser cone on the Dahl, you have air problems and if you do the infamous Haul_n "Dahl Flip" and see a lot of air then you have more subtle issues that might need to be addressed.
For 99% of PSD owners I think these two items are all that need to be added. Now if you're worried about air collecting in the fuel rails because of the dead ended fuel system or think your engine is too noisy then again IMHO all that the vast majority of PSD owners need is the $120 "cackle fix" that ties the two 1/8 in unused ports together with a bleed orfice and ties into tthe factory return line. I do think having some method to let any air that might collect in the fuel rails an avenue to escape is a good idea. However, it be most effective I think at that point the stock system needs to be modified to feed the heads from the rear and tying the two front ports for any air to escape since IIRC the engine sets at a slight up angle in the chassis. I would also install an in cab fuel pressure guage to monitor fuel pressure since some feel that this orfice thing might cause an issue. However, a lot of folks that installed this orfice type system have reported improvements similiar to a full blown flow the the head regulated return system. If my engine ever gets noisy or develops that dreaded "cackle" and effects performance then I would probably only do the $120 fix.
If I had an F-series and was looking for lots of power with bigger injectors, etc. then more radical fuel mods are probably required along with some mod to the HPO supply. However, I think I would only go that route after I had installed both an in cab Fuel and HPOP gauges before doing the horsepower mods and then determine where the problem might be. The only time I would consider a thru the heads regulated return would be if I was loosing fuel pressure based on seeing a problem as verified by installation of an in cab fuel pressure guage and after attempting to solve the fuel pressure problem by simply re-plumbing the factory system to either feed all four 1/8 fittings on each end of the head or feeding directly into the back of each head thru the fuel rail drain plugs. If you go with a thru the heads regulated system I would want one that feed the back of the heads thru the fuel rail drain plugs and would include getting rid of the factory filter altogether and putting one of the 2 micron filters that Haul_n is going to use along with an AirDog. At that point I would do the intank mods since you've addressed all the considerations except fuel temp. I have always been against doing a reg return w/o adequately addressing this air issue. This should address the air issue and I might even consider putting some sort of in bed tank and using that to fill up from the station and feed the stock tank from that in bed tank thru a Dahl 100 filter using something like another factory fuel pump. That should get fairly water free fuel to feed the AirDog and then the rest of the system. Alternatively, doing exactly what I think Haul_n is going to end up with is another good approach since he is addressing effective water removal, effective final injector filtering, and if the gets fairly "free air" free fuel to the pump whatever air issue remaining might be acceptable with the high flow thru the heads.
Again these are just some of my thoughts and obviously each will do whatever they feel comfortable with and obviously some will disagree on some aspects of what I think and that is fine. While not directly related I'll throw out the following for folks to ponder ....
The "idle knock" at least and most likely the "cackle" may or may not be air related, but can be aggravated if air is present. I believe that these two phenomenon are acoustic wave phenomenon. I took acoustic narrow band data on my vehicle and found on the a couple of occassions I would get a slight case of "idle knock". If you look at the two graphs
HERE you can see the harmonic nature of the "idle knock" phenomenon on the left where those harmonic peaks (see the dotted lines) were present and when the knock went away the lines were gone. All those graphs are of my vehicle which never exhibited any cackle problems at the known problematic cackle speeds and conditions. I never got any raw data, but based on what was posted in various wave files from members both before and after regulated return and in tank mods on vehicles that had reported "cackle" type problems, but even when the owners could hear the tapping/knocking the acoustic signature was still there. Unfortunately, I was not able to do any comparisons of levels before and after. If you look at the four graphs
HERE you can compare the acoustic signature of my vehicle against one that reported both "idle knock" and "cackle" issues.
