[Shotimes] Fuel Pump?

[Zach Leahy]

It's becoming better known now that any pump larger than a 150 lph is
too much capacity for the stock FPR at low engine speeds and loads,
this also casues the pressure in the fuel rails to be off which
results in issues of fuel mix due to the adaptive nature of the PCM.
The low speed low load times have too high of a pressure in the rails
due to the FPR not having the capacity and the computer will adapt to
it and change the pulswidth of the injector to get more in line with
optimal AFR.  the problem lies then in when you got to accelerate hard
and the fuel pressure goes from abnormally high back to the stock
pressure.  The computer still thinks the pressure is really high and
the engine will lean out.

If you plan on going for a very heavily modified SHO you will likely
need more fuel capacity.  That entails three items to be changed
really.  One the fuel pump will need to be sized accordingly.  Usually
the approach is to put in the 255lph unit and you will be all set.

Second, to counter the additional capacity of the pump, an upgraded
Fuel Pressure Regulator (FPR) is required.  Josh T has units for sale
that have plenty of capacity for any pump you choose.

Thirdly to utilize the increased volume you will need to put in larger
injectors.

As an added bonus with the Josh T setup, you can adjust the base fuel
pressure.  You could adjust the pressure to add a bit more capacity to
the fueling limits by raising the fuel pressure beyond the stock 39
PSI.  With plenty of pumping capacity you could get more fuel out of
smaller injectors and not get dinged with the adaptive nature of the
computer screwing it all up.

Clear as mud right?

So in simple terms, if you don't plan to do a complete fuel system
u[pgrade, don't put in a gigantic pump or you may run into problems
with lean mixes at WOT.

BTW I gleaned all of this from Josh's website.

Z

On 8/22/05, cmichaelo@optonline.net <cmichaelo@optonline.net> wrote:
> My old fuel pump, a 255lph unit, made lots of noise from when it was first put in. Especially when the tank was getting low.  This had something to do with the return fuel and the fact that the FP was way oversized for the fuel pressure regulator which caused the FP to vent pressure inside the tank.  I never really got to the bottom of it.
> 
> What size is your fuel pump?  Do you hear the noise all the time?
> 
> If you're going to change the pump yourself, please be careful.  Run your tank empty, or near empty, before you start on this job...if you start on it.
> 
> Additionally, several days before the job, douze the tank strap bolts with PB blaster several times.  As Zach said, they can be tough and can break.  Also, I usually knock on the bolts with a centerpunch to aid the PB to get around and to loosen up the bolt.
> 
> Michael
> 94MTX,green,BOS+,Koni/Intrax,Baer,Corbeau
> SHO items for sale: http://hometown.aol.com/cmichaelo/for_sale.html
> 
> ----- Original Message -----
> From: Zach Leahy <leahyz@gmail.com>
> Date: Monday, August 22, 2005 10:51 am
> Subject: Re: [Shotimes] Fuel Pump?
> 
> > It's nice to have a torch to heat the strap bolts up.  If you
> > don't it
> > is possible to break them.  Especially here in salt country, heat is
> > good.
> >
> > Z
> >
> > On 8/22/05, van Oss <vanOss@centurytel.net> wrote:
> > > There are instructions with photos on the FAQ site, shotimes.com.
> > >
> > > Nothing you've posted so far indicates that your pump is a
> > candidate for
> > > replacement.  It's not the sort of job to tackle unless you
> > really need to
> > > do it.
> > >
> > > VO
> > >
> > > ----- Original Message -----
> > > does that mean it's a really difficult job?  What does
> > fixing/replacing it
> > > involve?
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