[Gmecm] returnless fuel system

[Dustin Lof]

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> 1)  How does the single fuel line system work -- how
> does it maintain a 
> constant relative pressure across the fuel injector?
>  If the pump has 
> constant power on it, does it just "deadhead"
> against the injectors?  If 
> there is a regulator, how does this regulator work?
> 
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The Chrysler returnless systems have the filter and
fuel pressure regulator built into the fuel pump fuel
level sender assembly inside the fuel tank, so there
is technically a return line but it stays inside the
fuel tank, the filter is available separate but none
of my local dealers stock it or have any intention to
stock it so we do as they do and replace the pump. 
The tank would have to come out either way, saving the
customer the expense of removing the tank twice.

The Ford Mustang has a fuel pump control module
mounted in the trunk to vary the current (thus the
voltage)to the pump based upon measured fuel pressure
at the fuel rail. I am unsure what the other ford
models do exactly.

I have not seen a GM returnless system.


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> 2)  Could such a system be adapted to older EFI
> systems like a TBI or 
> TPI swap?  Could a single fuel line system be made
> to work on a TBI or 
> TPI install?  I assume this would mean either some
> code patches to the 
> ECM (i.e. a BPW adjustment based on MAP to
> compensate for the change in 
> pressure) or a standalone controller that would read
> fuel pressure and 
> adjust pump power accordingly.
> 
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Yes you can supply a constant pressure to the throttle
body, making sure there is still plenty of volume, I
have seen trucks come in with pumps that will only
make 10 psi of fuel pressure and they idle fine but
once you put a little load on the motor they bog and
even die due to low fuel volume, but you cant use a
dead head regulator like on a torch. the fuel pump
needs the constant flow if fuel to keep it cool. I
have seen adjustable regulators on eBay, a three line
regulator.  You would install this regulator somewhere
between the tank and the throttle body.  Block the
return fitting at the throttle body.  I have never
tested this but at low tbi pressures I would be
concerned with vapor lock. 

As for a tpi system the same would apply but you would
have to compensate your fuel tables for the increased
injector flow rate at high engine vacuum.



		
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