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Old 01-19-2013, 03:49 AM   #39
Baby steps...
bobnoxious67's Avatar
Joined: Jun 2008
Location: Marion, MA
Oddometer: 2,846
Originally Posted by fast4d View Post
most newer EFI systems run 'returnless'. there's no circulation of fuel

I would think the returnless pumps are cycled and don't run constantly on the same intensity therefore eliminating overheat conditions.
Originally Posted by VxZeroKnots View Post
At least on the Husky I have this is true.
Nope. "returnless" just means the fuel pressure regulator is in the tank...there is constant circulation, but it's inside the tank.

DepthFinder has it right

Originally Posted by DepthFinder View Post
Returnless simply means that the regulator is at or in the pump assembly. These systems will run a set pressure and modulate the IDC to account for changes in manifold pressure. I've never seen a pump that cycles (although many autos use voltage modulation to the pump to keep it quiet at low load and prevent regulator overrun at low IDC)

edit to add: There are also semi-returnless designs (such as BMW auto) where the fixed pressure regulator is contained in the external fuel filter with output to the engine and return from filter to tank.
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