[s-cars] Fuel Pressure Test Results

[Trevor Frank]

Ok a bit of info below some ramblings, but basically I don't think it is
the pump, I think it is the programming as it relates to your motor.
Fuel pressure is one thing but I wonder if it is to much advance that is
the real issue.  For me I ran between 45 to 75 psi on a stock pump
pre-boost, I was able to sort of change the a/f ratio but not a bunch.
Even with this drastic change on our crap gas I still got pinging.

It may be your pump it may not be, if you can back off on fuel pressure
you may have more luck, fuel delivery and pressure are nearly inversely
proportional. Of course you would need custom tuning to really get this
to all work.
   Think of it this way, you fuel pump has a certain amount of energy,
give more fuel pressure and you sacrifice volume, and visa versa. 

  I have a stock pump, and 57lb injectors, I don't get fuel starvation,
but I run 45psi un-boosted and am running 29psi on race gas so basically
75psi.  I had a fuel pump fail when I was running 75psi and 103psi
boosted I also had an issue with leaning out at the top end.  I think
that this is an extreme case and so I don't suspect that your pinging
issue is the same, I could be wrong.  I also had pinging with and
without higher fuel pressures.   

  I increased the fuel pressure because I was getting a bad a/f ratio
and high egt's on the dyno. 

  Since then Mihnea tuned my car, custom chips over the internet and
more recently in car tuning, with the above set up to very nice egt's,
good power etc...  This, custom tuning would be a good option. 

	In California I don't know of anyone with almost any software
that is packaged that doesn't ping, I personally have experience with 3
different "custom"/packaged software and all of them pinged on our crap
gas.  This is really no fault to the people who provided them, it is
just that no one expected 91 octane with ethanol or mtbe or whatever
they put in it these days.

  I am sure that my dyno numbers are not as good as Hap's but I suspect
that they are in the range of a well tuned RS2.  So although a larger
fuel pump may be a good idea or insurance purposes I suspect that your
pinging issue my not be the fuel pump.  The 044 as well as many cis
pump's I suspect would do the trick.

You might also want to check your check valve, if you look at the fuel
pressure after you shut your car down it needs to drop less than like
.5bar /30 sec or something like that, check the bently.  I suspect if it
isn't doing it's job then the pump could easily be pushing to much
volume at almost any pressure, since this is a recirculater.

Oh ya did I say that custom tuning would be a good idea?

-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com] On Behalf Of Dave Forgie
Sent: Sunday, July 25, 2004 10:19 PM
To: Sean Douglas; s-cars
Subject: [s-cars] Fuel Pressure Test Results

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
off)
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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