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Old 05-11-2012, 01:44 PM   #1
bschweig
Scooby Newbie
 
Member#: 179006
Join Date: May 2008
Location: Boulder CO
Vehicle:
2008 STi GR
OBP

Default Walbro 416 LPH In-Tank E85 Fuel Pump installed in 08STi, issues and solutions?

We recently installed one of these in my 08STi. We believe it is one of the first applications of this in the front range area of Colorado. We are having some subsequent issues that I hope folks with an interest in this might help us solve.

The car is a 08STi with extensive mods (i.e., Benson sleeved block, Cosworth internals, DOM3xtr, all supporting stuff; current tune is 435 whp 410 wtq at 24psi and 11.1 AFR on a dynodynamics). Its a daily driver that sees the track a lot.

The fuel system has the in tank 416lph with dedicated hard wiring, a Aeromotive EFI FPR, Aeromotive in line filter (the e85 spec one), AP fuel rails, and Bosch ev-14 1000cc injectors. We installed the 416 in place of a walbro 255 that while working fine was likely limiting or will be limiting when I go roated on the turbo.

The car was retuned after the pump was in. Base pressure is around 60psi at start up, rising to around 80ish (I think) at WOT. We were able to drop the AFRs to around 11 from around 12 on the previous tune and pick up around 20 whp.

The install of the unit in the plastic in tank pump holder was a bit tricky. This pump has a fat base and is slightly longer than the old 255. We had to grind out more of the plastic housing, etc. On the first attempt we left too much fuel hose between the pump and the inlet and after a few days it pushed the hose off as the pump slide sideways in the housing. I lost fuel pressure and barely limped back into the shop. We redid the install, grinding out more material and shortening the hose so the housing unit clamps down better and doesnt alter the pumps orientation (we hope). We will redo the install one more time using AN fittings to really make it solid.

The issue we are having is as follows. At very light throttle pressure there is a noticeable and annoying bucking/jerking. This was not present with the 255 (which was on the OEM relay). This rough running may exist at full throttle but its just not noticeable. There is nothing in the tune that we can see that would cause this, so we think it is the new pump or its wiring (or fuel lines?). With the hard wiring the pump runs at 100% all the time of course so perhaps at light throttle there is too much fuel pressure or the return line is not sufficient?

Does anyone have any suggestions or thoughts? We are considering a fuel pump control unit (like the Aeromotive Fuel Pump Speed Controller) but this is pricey and its not entirely clear it will help?


Note - I am not a fuel system expert by any means, so please be gentle.


thanks!
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Last edited by bschweig; 05-12-2012 at 12:15 PM.
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