bombone

just got a holley carb,put the gauge on and it was reading about 7.5 for fuel pressure,but after about 10min the pressure starts to go down and finaly there is none after about 15min. thinking it was the fuel pump i went and got an electric pump. put it on the next day and the same thing happens again. does anyone know what could be the problem.

Hornblower

Not sure which year Mustang you have, but the earlier ones had a filter in the tank attached to the sending unit. That filter, called a "sock" could be picking up trash from your tank when it is under pressure, so finally gets completely stopped up after awhile. Just a guess....But, easy enough to find out. Drain your tank and take out the sending unit to inspect that sock and to get a look around inside your tank for signs of rust.

bombone

66 is the year... and thanks for the info i will ckeck that out

bombone

it never turned off .there was just no gas in the filter so i turned the car off but the pressure totally dropped so the gauge said

Hornblower

So the car still ran as usual, just no pressure as per the gauge? Are you reading the original gauge? Try this. Take the gas line off at the carburetor and put the end of the line in a jar. Have someone try to start the car and see how much gas comes out of the end of the line. If it is a good steady flow, then you don't have a problem other than the gauge is faulty. If there is very little flow, then check both of the filters.

THUMPIN455

Did you put the electric pump back near the tank, or is it up front under the hood? Back by the tank is much better as electric pumps push better than they pull.

If it is sucking air through a leak in the line, you can lose pressure like that as well. If you have the pump in back, the leaks will be obvious in the line, if the pump is under the hood they are difficult to find.

Hornblower has a point as well, you probably have a large amount of debris floating around inside the tank, it could be plugging the pickup.

If it were mine, it would be getting a new line, the pickup/tank checked and possibly replaced, and the electric pump placed back by the tank away from moing suspension parts.