Electric Fuel Pumps

[Carl Summers]

Hi Greg,
    The controller I was using was an Autronics box....it has no feedback to
watch fuel pressure and adjust PW...The fuel pressure drop has always
happened on the Blown alcohol datalog stuff I have looked at when shifting
gears, and I noticed the rise in AFR upon full throttle shift when I was
datalogging this but was only about 3/4 of an AFR on the Horiba and if my
memory serves me was about .4 seconds....but, when it would almost stall on
upshifts rpm had dropped about 2000 whereas full throttle was only around
800...my guestimation on what happens is the pump is pumping 100gph(for a
number) and immediately changes to 80(for a number) it produces a mass
volume hole that the bypassing regulator on the end of the rail could not
react fast enough to...I don't know the physics of why...I just saw it and
can't see how it could have been cavitation if it would accelerate fine
without a gear(RPM) change....someone on this list should be able to
enlighten us though...(I bet it'll be you Greg after you think about it a
while, I've seen you come up with some pretty brilliant stuff)  ttyl
-Carl Summers

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of Greg Hermann
Sent: Thursday, February 10, 2000 4:27 PM
To: diy_efi at diy-efi.org
Subject: RE: Electric Fuel Pumps


>Hi Greg,
>     Unless you plan on running some sort of large accumulator the
>mechanical/gear driven pump will cause many tuning problems on shift as
>engine rpm goes down and so does pump....fought that on that 1600hp boat
>engine with the turbo 400.. the fuel pressure would drop to below 20 psi on
>upshift and lean backfire....crazy thing was (not so crazy though, less
>torque meant more drastic rpm changes on upshift)it was worse the easier
you
>were on the throttle so didn't notice it as bad until I was going back over
>the driveability stuff after verifying full throttle....thank god for
>datalogging....would have never found it...ended up with an elctric fuel
>pump set up to run while in 1st and 2nd gear and shut off in third...got
>that straightened out and no probs other than the normal retune from the
>engine dyno to the real world...just some insight...ttyl
>-Carl Summers

Hi Carl--

Thanks for the tip!

Hmmm.

Gonna hafta think this one through. I am planning on using an accumulator
on the intermediate pressure part of the fuel system--the FEED TO the
mechanical pump. Had not thought about using one on the HP side of it,
particularly cuz I was thinking of adjusting the rail pressure to suit
varying engine operating conditions, and an accumulator on the HP side of
the system would destroy the response time for these rail pressure changes.

But I have a funny feeling that you were getting the anomalies on the HP
side! This appears to be a fun puzzle--not real obvious to me why it was
going on, but that doesn't mean it couldn't! Just almost seems to me that
you had to have some cavitation at the inlet to the mechanical pump for
this to happen, but ????

An electrical (positive displacement) pump will definitely recover from a
suction cavitation event quicker than a mechanical one, cuz the motor will
pick up speed as soon as the vapor is in the pump--which is not true with a
mechanical pump.

Was your ecu correcting injector PW for fuel rail pressure on the engine in
question??

Greg
>

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