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Old 01-19-2013, 04:49 AM   #39
bobnoxious67
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Joined: Jun 2008
Location: Marion, MA
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Quote:
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.
Quote:
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

Quote:
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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