Fuel pump leaking?

[dst2680]

My 75 coupe deville is leaking gasoline from what I am assuming is either the fuel pump or its rubber line located in the front lower part of the drivers side of the engine. The steel line looks fine. It's hard to tell if it's leaking from the pump itself or the rubber hose as the entire hose is wet. It only leaks while the car is running. Any guesses? The car runs fine currently, but the leak is pretty significant while it is running. If it is the pump, does anyone have suggestions on a good replacement? It is the 500ci engine, and the parts are likely original due to the low miles. Thanks!

[chrisntam]

My money is on the line leaking.  But it could be the fuel pump.  Run it for a very short time and shut it off.  Start from the top of the fuel pump and feel for fuel, working down towards the line.   Maybe get a flashlight so you can see better.  If it were me, I'd replace the rubber line first, only costs a few bucks, get worm gear clamps.  Be sure the engine is cold when you replace the line and make sure you have a drain pan under the pump when you pull the line off, fuel will drain out.  Once the line is replaced, start it to see if it leaks.  If it leaks, then the fuel pump.  Rock Auto on line or your local auto parts store to buy a pump.  If you do the  fuel pump, be sure to use a line wrench when disconnecting the metal fuel line.

chris.

[Smedly]

those pumps generally have a small hole which the gas will come out of when the diaphragm inside lets go. and it usualy only comes out when the engine is running. My guess is the pump is no good.

[Scot Minesinger]

If it is the original fuel pump (traces of blue paint), it is just a matter of time anyway, and it should be replaced at your convenience rather than later at a most difficult time.  I agree replace the rubber lines first to try and discover leak source then pump if that does not cure it (replace rubber hoses anyway front and rear if original).

[Smedly]

it should also be mentioned that if it is the diaphragm in the pump then the fuel will also start going into the bottom end.(mixed in the oil) I would not run anymore then necessary until you find the source of the leak

[TJ Hopland]

If its not original I have seen it more and more lately where the 'nut' that holds the steel line is not very well attached to the body of the pump so if you are not extra careful when installing the steel line you can get a leak. 

Anyone ever cut open one of those pumps?   Is most of it just full of fuel?   I assume the diaphragm is up in the cast part like every other pump?   What was the reason for all that extra space?  I can sort of see making room for the filter but they appear to have had the big can before and after the filter. 

[m-mman]

The large 'can' is a reservoir. First it contains the (long style) filter, but also stores an amount of fuel.

A common problem for an A/C car with limited under hood airflow and a carburetor is vapor lock.
Get gas hot enough and it will 'boil' (turn from liquid into vapor) A carb fuel system can not handle vaporized fuel. It cant be pumped and it cant pass through the carb. A carb system runs around 7-10 psi

Fuel injection systems run high pressures in the fuel line (right up to the injector ports) and higher line pressure need higher tempt to boil/vaporize. FI systems run 20-50psi (varies with year and makes) Under hood temps dont get hot enough to vaporize fuel at this pressure.

In order to prevent boiling/vaporizing Cad ran a completely separate line BACK to the tank. Anytime pressure got over 10(?) psi it meant the the engine did not need the extra amount pumped and the valve opened and let a stream of fuel return to the tank. This return of fuel (and pick up of fresh fuel from the tank) provided a COOLING effect on the fuel pump.

However if the driver did open the throttle there had to be a small reservoir that could be drawn from to keep the carb filled, hence the can.

[jaxops]

My money is on the line leaking.  But it could be the fuel pump.  Run it for a very short time and shut it off.  Start from the top of the fuel pump and feel for fuel, working down towards the line.   Maybe get a flashlight so you can see better.  If it were me, I'd replace the rubber line first, only costs a few bucks, get worm gear clamps.  Be sure the engine is cold when you replace the line and make sure you have a drain pan under the pump when you pull the line off, fuel will drain out.  Once the line is replaced, start it to see if it leaks.  If it leaks, then the fuel pump.  Rock Auto on line or your local auto parts store to buy a pump.  If you do the  fuel pump, be sure to use a line wrench when disconnecting the metal fuel line.
chris.

I would recommend Texas Johnny and get an alcohol resistant fuel pump replacement in the OEM styles.http://cowboyjohnsautoparts.com/antique-car-parts.html