[s-cars] Fuel Pressure Test Results

Dave Forgie forgied at direct.ca
Mon Jul 26 01:21:33 EDT 2004

S-gruppees:  We (Sean Douglas, Dave L. and me) need your collective wisdom.
We are still (I know, its boring but) trying to solve are RS2
install-related pinging at higher boost pressures (Sean actually had some
pinging before with an MTM+1 chip set).  I have contended (unsuccessfully)
that the new batch of turbos is either over spec OR the OEM pumps aren't up
to the task (the List said NO to both of these).  Last weekend Sean and I
tested my fuel pumps fuel flow (700 cc in 15 sec at 11.75 V - within Spec
and identical to Sean's).  This weekend Sean tested his fuel pump pressure
with these results:

With just the fuel pump on = 57 psi  (3.93 bar at 1 bar = 14.5 psi) Spec =
58 to 61 psi
Residual pump pressure = 52 psi (spec 49-54 psi) (after turning the pump
With engine at idle = 50 psi (3.45 bar)  (this would be with the manifold
under vacuum)
(No tests yet under load)

I am confused.  In my calculations with a 4 bar fuel pressure regulator and
an engine making 24 psi boost (for example), I thought the fuel pump should
have been able to make 4 Bar x 14.5 psi/Bar = 58 psi plus 24 psi boost = 82
psi (5.66 Bar) on a static pressure test.  If I am right, then we have the
reason for the pinging - not enough fuel pressure at the injectors under
load.  However, then I have to wonder why the OEM pump (and fairly new one
at that) isn't up to snuff (back to the Audi Sport pump or another OEM S4
pump?).  IF I am wrong (I have been known to be wrong) in interpreting these
results and how the FPR is supposed to work, I (We) need to know why we are
wrong on this.

Your wisdom is required. (Please).

Dave F. (on behalf of the Sean D. and Dave L.)

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