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      12-01-2012, 03:22 PM   #314
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Drives: 2007 335i, 2015 M3
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Originally Posted by trbolexis View Post
Disassembly of the stock fuel sending unit is a delicate process, and when it comes down to it, you are essentially breaking it apart to install the pump.

The suction valve at the bottom of the assembly is not regulated at +70 PSI in factory form. Pushing the pressure through it up that high is going to cause failure at some point; but i have no data on that point currently. To add to this note, there is also no sealing surface for it to be completely "fuel tight" at the base when held on by zip ties. -- Imaging having a huge boost leak all before your throttle body because you didn't feel like putting a clamp on the coupler. You would be able to hit boost certainly, but with very little wow effect; and all that leaking boost out of the system is going to cause the turbo to have to work harder to maintain pressure. As a result, it may over-run, and fail prematurely. Another note, the leaking boost around before the TB is also going to cause your boost to fall off at higher RPM as your turbo falls out of its efficiency range. -- Remove the word turbo from all that i previously mentioned, and sub in fuel pump. Remove 'boost leak', and sub 'fuel leak'. Remove TB, and sub 'before your HPFP'.

I think you get the point. The DIY procedure is going to essential cause a fuel leak in the low pressure system which makes the pump work harder, and also causes loss off efficiency as pressures go UP (and the pressure in the LP system is much higher than most any other vehicle in production, period.); this is why you want to leave the stock system intact. The booster pump will NOT cause a leak, and will ONLY raise fuel volume flowing to the HPFP. It gives you complete peace of mind when driving your car on long trips because you know that your stock siphoning valves and fuel regulated systems are 100% fail proof, and that your fuel gauge is accurate.
From what I have seen with the OEM setup the siphon valve sits in position using a plastic ridge, and is held down by the weight of the OEM fuel pump. In the DIY there is a ziptie holding it in that same plastic ridge in addition to the weight of the Walbro pump sitting right on top of it just like the OEM setup. Your concern there is unfounded. If there was an issue then we would see the low fuel pressure drop in logs which none of the 5-6 people who have done the
DIY are seeing. Overall it's been a solid low fuel pressure setup. Different strokes for different folks.

That isn't to say your inline pump can't be a solid setup either. With inline pumps normally they reduce volume / increase wear on the in tank pump when they are not pumping, becuase they become a big restriction. Does yours pump full time or only during wide open throttle?


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