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2g AWD DSM Fuel System De-mystified

dexterholland04

Proven Member
756
104
Jan 1, 2007
Rush, New_York
I figured I would post this as a Tech Article, since I do not believe it has been covered in one convenient, concice, article.

The 2g AWD DSM has a weird fuel tank setup. It has two saddle tanks, one on the driver-side and one on the passenger-side. The passenger-side contains the fuel sending unit and high pressure pump that feeds fuel to the engine. The driver-side assembly contains an additional low pressure siphon pump that pumps fuel to the passenger-side saddle tank. That’s why the 2g AWD fuel sending unit has three ports on top of it: high-pressure output to the motor, low-pressure return from the fuel rail/fuel regulator, and low pressure input from the driver-side saddle.

If you look closely at the fuel sending unit when it is out of the tank, it has a small plastic “Y” that takes the returned (unused) fuel from the fuel rail and the fuel being pumped from the driver-side saddle as inputs and the output of the “Y” just drains back into the driver-side saddle. It works on the Venturi Drain principle, where the pump in the driver-side saddle always puts out a constant pressure, and the pressure varies coming from the return line: higher pressure under idle and normal driving, and lower pressure under WOT conditions. Therefore, when the input pressure from the siphon pump is greater than the input pressure of the fuel return (into the “Y”), more fuel is drawn into the passenger-side saddle from the driver-side saddle. Conversely, when the input pressure from the siphon pump is less-than the input pressure from the fuel return, the driver-side saddle pumps much less fuel into the passenger side saddle.

The Venturi Drain is located directly under the fuel pump, in the attached picture. (Thanks, STM - for taking such AWESOME pictures!)

More on the Venturi Drain principle:
[ame=http://en.wikipedia.org/wiki/Siphon]Siphon - Wikipedia, the free encyclopedia[/ame]
 

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