DrX

iTrader: (7)

Just did some observation/testing on the returnless fuel module which I am converting to return style to help keep the Radix well fed.

Significant observations include:

The equalization valve alone was insufficient to keep up with the Walbro GSS340. The bucket was drained in no time and aeration was occurring even though the fuel level on the outside of the bucket was much higher. The Walbro actually seemed to be sucking fuel through the valve faster than it could flow into the bucket on its own(along with air from above).

With some back pressure applied to the outlet line, my modified venturi system functioned well to aid in filling the bucket, but I am uncertain as to whether it was enough to keep up with the Walbro.

Once a certain pressure level is reached, the relief valve on the Walbro opens and some fuel is lost from there. They are designed to leak somewhat- less so for the high pressure versions(like the GSS340). This is why some advocate sealing the relief valve shut with epoxy(with certain risks) for higher HP applications.

I did not return the fuel to the module in order to simulate a WOT situation where the regulator would be returning little or no fuel. At low fuel demand levels the FPR would also be returning significant fuel to the module to keep the pump immersed.

This may help to explain why some of us with certain 04+ returnless systems are experiencing fueling issues. This would indicate a possible need for larger or multiple equalization valves. Particularly when the venturi fill feature has been disabled(i.e when using a Walbro as a direct drop in replacement for the OEM fuel pump with no other modifications). Alternatively, one could cut a hole in the bottom of the module to allow better equalization, but the bucket would also drain out as fuel sloshes in the tank. You would have to be maintain a fairly high tank level to prevent aeration under acceleration or cornering as there are no baffles in the plastic tanks.

Here are a couple of pics of the modified module(Mark I) and the bottom of the module in my OEM configuration.

BlownChevy

iTrader: (20)

Now try putting the same restriction on the pump as a fuel system would have....Do you really think the fuel pump in real life conditions is sucking the bucket dry? Try the same test with the stock pump, results will be the same. I DO NOT see this being a viable option. Even at WOT you are not going to suck the bucket dry, I gurrantee the return line is dumping plenty of fuel back in the bucket.....

DrX

iTrader: (7)

It was tested both with and without restriction as flow would be much greater at 0 psi. The test was not intended to compare the performance of the different pumps, but rather the operation of the module. The flapper valve in this design was only intended to prime the module and to close as soon as the venturi system filled the bucket. I am not comfortable that the FPR in this design would be returning any fuel to the module under conditions where the fuel pressure drops significantly below that which it has been designed to maintain. Putting a hole in the bucket would definitely not be my preference. I would rather restore all of the factory functions of the module if possible. A Racetronix style pump with an additional outlet to drive the venturi would be helpful in this case.

zippy

i have worked on my share of returnless trucks that are running 50# injectors and running them to over 100% duty cycle without any excessive pressure drop. i've only worked on one that had a pressure drop problem that caused the pump to not be able to keep up with the injectors. i don't see a problem so far with the returnless system and it's ability to feed bigger power levels other than it requiring more injector to do so.

DrX

iTrader: (7)

There are many different designs of returnless modules and they each have their own idiosyncrasies. Some seem to be more amenable to modification than others. I am only talking about 1 specific module here. Although others may share similar features. For example, the module in the 6.0L trucks is a different design than mine and it seems to respond well to a pump swap.

LVSTOGOFST2002

iTrader: (3)

so why not swap to a 6.0 truck module, and skip the bs?

03sierraslt

iTrader: (22)

What is different about the 6.0 truck module? I know my injectors are at 97% duty cycle and I am not really pushing crazy boost #'s (8-9lb)

DrX

iTrader: (7)

I don't have a 6.0L style module to look at but from the pics it appears to have a different regulator setup, different vent connections, different pump and a different filter. From what I recall of the drawings, the bulkhead also differs. Not sure how the overall dimensions of the modules compare(I had considered possibly matiing 2 different modules together). Maybe someone can confirm this, but it also looks like the waste from the regulator may drive the venturi system rather just spilling back into the bucket as on my OEM setup. In that case changing the pump would probably have no effect on the mechanism for keeping the bucket filled. I don't recall anyone with these modules complaining of fuel issues before.

dewmanshu

iTrader: (4)

seems to be a common finding lately.

LVSTOGOFST2002

iTrader: (3)

i agree. so are we of the correct assumption that the 03+ fuel system design on 5.3 trucks, is flawed? anyone willing to bite the bullet and buy a 6.0 module to test?