[DeTomaso] Fuel Pump Question

[Ken Green]

Art,
   
       I think mechanical pumps have some kind of spring on the diaghram to limit the pressure out of the pump.  Normally, I think that pressure is what you see with the fuel pressure gauge.  As long as the pump has excess capacity, the float bowls should be full, and the pressure should not drop.  If the pump falls behind, then it's pumping as much as it can, the internal pressure control does nothing, and I think the pressure will drop below the pump's design pressure.
   
        I'm sure someone else can explain this a lot better than I can, but I think this is the basic operation.
   
  Ken

Art Stephens <artstephens at charter.net> wrote:
  Thank you Doug and Jack for the explanation. I think I got the going 
lean part. Hypothetical situation, I have my car on a chassis dyno running 
wide open for a few seconds. Fuel pressure does not drop. That would not 
necessarily mean that I'm not at risk of going lean, would it? If I am 
using fuel faster than the system is providing it, could my gauge still be 
showing full pressure until the bowl actually empties? I'm a little 
concerned about getting a false sense of security by watching the gauge for 
the brief time the car is wide open on the dyno.

Art



----- Original Message ----- 
From: "Doug Braun" 
To: "Art Stephens" 
Cc: "DeTomaso Forum" 
Sent: Thursday, July 12, 2007 9:44 AM
Subject: Re: [DeTomaso] Fuel Pump Question


> Art,
>
> The richness of a carb's mixture is dependent upon the level of the fuel 
> in
> the float bowl. Any reduction in the bowl level leans out the mixture
> because the venturi effect has a harder time sucking fuel out of the bowl
> through the jets. If the fuel pump can't quite keep up with the demand, 
> the
> fuel level in bowl will fall and the engine will run lean. You're correct
> that if the bowl level falls far enough the engine will die but the danger
> is that the fuel level falls but not far enough to kill the engine. You 
> can
> check for this by reading your spark plugs right after a hard run, by 
> using
> a fuel pressure gauge that you can read under wide open throttle or a
> wideband O2 sensor. I chose to mount a lighted Autometer fuel pressure
> gauge on the passenger side engine cover that I can read in my rear view
> mirror. This also tells me when my fuel filter is getting too dirty.
>
> Doug Braun
> blue 73L #5505
>
>
> -----Original Message-----
> From: detomaso-bounces at realbig.com
> [mailto:detomaso-bounces at realbig.com]On Behalf Of Art Stephens
> Sent: Wednesday, July 11, 2007 5:34 PM
> To: detomaso at realbig.com
> Subject: [DeTomaso] Fuel Pump Question
>
> While running at wide open throttle and emptying the fuel bowls,
> wouldn't the engine just die instead of going lean? It seems that it 
> would
> die and then briefly start up as the bowl started to fill and then die 
> again
> repeating the cycle as long as your foot was still in it? Maybe you would
> be lean for an instant, but then it dies? If it was running that bad, 
> you
> would likely do something different and not continue to run it like that. 
> I
> guess if the pump was just a hair short of supplying enough fuel, it 
> could
> theoretically give you a lean mixture that would make it go like hell
> without going so lean that it stumbles?
>
>
>
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