Proper Fuel system pressure...

[MIGHTY 8]

Hello,

As I have metioned before on other topics, I have recently been having problems with my car running rough/poorly and have been trying to pinpoint the problem.

I have owned this same car for many many years, and belive I came upon something yesterday.

Prior to topping off with fuel, I noticed the gas cap had a lot of pressure built up as I was removing it.

Didn't make too much about it at the moment, but after getting back on the road, It appeared the car performed better?? Not perfect...just better.

Having just had a new elec. pump installed (by a mechanic) I am curious if someone here can explain how fuel pressure is maintained inside the fuel system, how does it bleed any over-pressure, and if a high output fuel pump was inadvertaintly installed, can it be the cause of my malaise?

Thanks in advance,

[124JOE]

if it had too high of pressure it would flood out rightaway and wont run
carbed pressure 4lbs
injector pressure 35 lbs

[Dales78]

Those pressures sound about right but they are between the pump and the carburetor (or injection system) and not inside the fuel tank.

It’s most likely that what you heard when you removed the gas cap was negative pressure (vacuum) that forms in the tank as the volume of fuel drops. If the tank venting system has a problem (that is, it doesn’t allow air into the tank to replace the volume of fuel that has been used) it can cause the engine to run poorly because the vacuum inside the tank prevents the pump from delivering enough fuel pressure to the carb. So pressure in your tank may be the problem but not because of your fuel pump.

After you filled your tank the other day, how long was it before she started acting up again? Does your car generally run ok for a few miles then go bad? I’d try running it for a bit without the fuel cap (to vent the tank) just to see if it helps.