RE: Fluctuating fuel pressure

[Steven Charette <stevec@xxxxxxxxxxxxxxxxxxxx>]

Ahh, that makes sense... the '64 just mysteriously shut off a couple of
(inopportune) times on our trip.  Always on hot days and after sitting for a
while (fuel or food stops).  Most times it was as I was pulling out into
traffic - ACK!  

Had the same trouble with the Travco last week when trying to level it - had
just gotten off the highway and it idled as we checked in to the campground.
It then sat and idled again for a while as we attempted to level it -
finally stalling and not wanting to start again (we ended up changing the
bed so we could at least sleep head up - ever try to sleep with your head
lower than your feet?).  Started and ran great on the way home yesterday.

This does make perfect sense - I hadn't had vapor lock in such a long time
it never occurred to me.  Is it possible that what Rich is seeing is vapor
pressure overcomes the pump pressure and prevents adequate flow of fuel?

SC

-----Original Message-----
From: Schuyler Wrobel [mailto:sky62@xxxxxxxxxxxxx] 
Sent: Monday, August 03, 2009 7:33 PM
To: 1962to1965mopars@xxxxxxxxxx
Subject: Re: Fluctuating fuel pressure


hey Rich, here is something from my Don D. folder-

Pascals law fo Fluid Dynamics states that pressure is distributed with equal
force in all directions.( We teach this when teaching brake systems )As long
as the supply of fuel to the pump is sufficient (more than can be used ). As
fluid or fuel is used pessure will fall (at high RPM) It should not fall be
low 5 ideally.
I would go ahead and run it. If it is not enough you will know the first
time you wack the throttle Don Author of Return to Deutschland (True
Adventure) Old Reliable (Mopar)

One of the big problems facing us to say when using mach fuel pumps is that
we are pulling fuel from the tank.
When we reduce the presure in a liquid we also reduce its boiling point or
point when it convetrs from a liquid state to a gas state.
It used to be  fuel manufacturers added  chemicals to reduce the tendancy of
fuel to boil and cause what we commonly called vapour lock.  Now because all
cars currnetly in production have fuel injection with a line running full
pressure from the tank to the injectors there is no longer any reason to
worry about vapour lock conditions. However for us  with older cars with
conventional fuel pumps which pull fuel at low pressure from the tank to the
pump and are engine mounted (so they absorb heat from the engine,) it can be
a real problem. Enough of a problem in some cases the engine will
mysteriously quite after several successive stop lights in hot traffic or
suspicious no start conditions after a hot soak (sitting hot shut off while
you go inot a store for a loaf of bread for instance. When you go to restat
it doesnt want to start. Because it is mysterious often the ignition gets
the blame . In fact it is the fuel pump absorbing heat. Gasolines with
ethonal are even worse for this condition. One cure that works well on BB
mopars is to build a very thin shiiled of aluminum and mount it on the fuel
pump attaching bolts so it shields the fuel pump from the front of the
engine block which it almost touches at the side or business end of the
pump. This will usually cure the problem on most cars and on some that are
real severe at least bring it to almost never status.
The other solution that Bob aluded to is to install an electric pump.  
The only problem is if you install a garden variety pump it may not be able
to keep up and if shut off just makes the regular pump work harder severly
limiting it violume. A good electric pump that will handle everything by
itself is often very noisy  which is something that is not a lot of fun in a
street car.  I think there are some new brands of pumps that are not so
noisy out there now but I havent tried them. I did find a mech pump recently
that has its business ends lower and farther away from the block. I am
getting ready to try it out to see if it is a reasonable solution.
Don
Author of
Return to Deutschland (True Adventure)
Old Reliable (Mopar)

maybe some of this will help?

Schuyler 62 Dodge Dart 440 wagon w/ Poly 318
  <http://www.1962to1965mopar.ornocar.org/ml-wrobel62.html>
FYI - I Do the Decal designs for the Poly head 318 and more! email me with
your needs -
  <sky62@xxxxxxxxxxxxx>



On Aug 3, 2009, at 11:58 AM, Rich Kinsley wrote:

>
>
>
> Rich Kinsley '64 Dodge Polara 4dr 318poly w/goodies
>
> Things seem to be getting worked out nicely but I do see a puzzling 
> phenomenun. I set the pressure regulator to 6psi, let it run till it 
> warms up and it drops maybe down to 4psi. I swapped the press 
> regulator and it did the same thing. I guess I should get another fuel 
> pressure gauge and install it before the regulator to see if the pump 
> output is consistent.
>
> Anybody see a similar thing happen? It actually dropped to 2.5psi once 
> when it got real warmed up. It hasn't affected the performance though.
>
>
> ----
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>


----
Please address private mail -- mail of interest to only one person --
directly to that person.  I.e., send parts/car transactions and negotiations
as well as other personal messages only to the intended recipient, not to
the Clubhouse public address. This practice will protect your privacy,
reduce the total volume of mail and fine tune the content signal to Mopar
topic.  Thanks!

'62 to '65 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html. 


----
Please address private mail -- mail of interest to only one person -- directly to that person.  I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic.  Thanks!

'62 to '65 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html.