[eschaider]

Sunman,

Have you tuned an EFI engine and tested your theory against ECU reported/recorded AFR or lambda targets? Have you measured the varying impact across the engine's part-load, part throttle driving rpm? When you do, you will find data that is both surprising and also nonsupportive of your argument.

You are dealing with relatively low differential pressures at the injector at part throttle / closed throttle. The reason for this is the vacuum present in the manifold at low engine speed and small throttle openings.

Ford's pressure compensated fuel pressure regulator adjusts fuel rail pressure for observed / measured manifold vacuum in these low throttle opening high vacuum situations to preserve the base fuel pressure differential across the injectors. If you have a manifold vacuum of 17 inches at idle and higher cruising speeds when you take your foot off the throttle, you are changing fuel rail pressure by more than 8psi.

Ford has a preference for a 39.15 psi differential pressure across their injectors. At idle, this can drop fuel rail pressure to 30 psi. On the highway, when you lift your foot off the throttle, the pressure drop is exaggerated because of the higher engine speed and, again, the closed throttle.

Any restrictions or impediments to flow in the return line will upset the fuel available to the engine at the injector when you tip in your throttle. The result will reduce the attractiveness of the car to drive. The engine can behave weak, non-responsive, and then surge with power.

This discussion is not about whose dog is bigger. It is just about the real-world experience working with these systems and what makes engines, tunes, and cars more or less drivable. If the OP wants to put the return line into the bottom of his tank, by gosh, that is his call, his car, and his money. He should absolutely do it! The information and experiences I am sharing are for knowledge. If he wants to discount them for any reason, that's his call and his right.

One of the more daunting challenges with the Ford OEM EFI systems is Ford's reluctance to share the programing tools and methodology they have used. Many aftermarket shops like HP Tuners, SCT, and others have done a pretty impressive job laying out the Ford maps, logic, and tuning parameters. The most important thing to remember is that they have used a trial and test approach that, while validating what they are working on, does not give the complete picture of all the variables the ECU is using and how it uses them.

The switch to an aftermarket ECU is a breath of fresh air for documenting how the EFI system handles differing engine situations. It also brings a wealth of engine protection tuning, data logging, launch, flex-fuel capabilities, and much more. The most significant barriers to using one are cost and emissions testing in your home state.

Some excellent low cost EFI systems leave little to want feature-wise in their implementations. Some are priced as low as $1,500 or less! If the emissions Nazis don't shoot you down, the aftermarket approach is the way to go. If they shoot you down, a good tuning software package like the HP Tuners offerings will help you get the most out of your OEM ECU but, and this is a big but, the now modified code in the OEM ECU may not pass emissions testing.