Electric Fuel Pumps

[Greg Hermann]

>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
>
>-----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 11:01 AM
>To: diy_efi at diy-efi.org
>Subject: Re: Electric Fuel Pumps
>
>Hi Walt--
>
>Didn't realize that you had good pump data at hand!
>
>I have been pondering using a primary in tank pump, only need maybe 7 to 10
>psi output,  but 60 to 80 GPH would be a good idea. Thinking I will use a
>mechanically driven gear type secondary HP pump to feed the rails. The
>mechanical pump is no problem to come up with or drive, but I (naturally)
>want something quite reliable and relatively insensitive to dirt in the
>tank.
>
>Electrical system will be 24 vdc. I have been thinking pretty seriously
>about just using a 24v. marine centrifugal bilge pump in the tank--35
>HUNDRED GPH, but just run it right up near the (about 7 psi on gasoline)
>stall head on its curve--very nearly constant output as to pressure that
>way at such a low flow rate for the pjmp's size, and thus be able to make
>whatever primary fuel flow I need in a laugh. And--at such a low peak flow
>rate relative to the size of the pump, relatively low current requirement
>for the pump motor, and hence very reliable and cool running. Clearly not
>sensitve to dirt, either.
>
>Any thoughts or other suggestions for an in-tank pump that would fill this
>general need??
>
>I would think that running a HP in-tank fuel pump , but regulated to the
>low output pressure I need, but at 24 v instead of 12 v. MIGHT just goose
>the (pump speed and) volume of a fairly ordinary in-tank pump up to what I
>need with no adverse effects on the pump motor so long as the load on it
>was light due to the low pressure---
>
>Regards, Greg
>
>
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