Re: Fluctuating fuel pressure

[Schuyler Wrobel <sky62@xxxxxxxxxxxxx>]

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.
>
>
> ----
> 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.