Fuel pressure issue only with tank near empty

[Mad_Trbo]

Have any of you ever experienced an issue with maintaining fuel pressure at start up that only shows itself when the tank is close to empty. You turn the car on and the fuel system pressurizes, I know many of us have expressed issues with the injectors leaking or the fuel pump allowing pressure to bleed off.

I believe my issue is with the fuel pump bleeding off but it only seems to be a problem when the tank is approaching empty. Have any of you ever seen or experienced this with your own buicks?

 

[pacecarta]

you probably are empty and sucking in air , run with low fuel level isnt good for the pump and definitely dont boost with low tank .
if you want to know if you are sucking air , remove the fuel rail shrader at end of fuel rail , install a clear drain hose (clamp it ) and put other end in a gas can , disconnect the hood lamp wire and loosle connect to the fuel pump prime ,
if you are sucking air youll see the bubbles pump through the clear hose

 

[Mad_Trbo]

you probably are empty and sucking in air , run with low fuel level isnt good for the pump and definitely dont boost with low tank .
if you want to know if you are sucking air , remove the fuel rail shrader at end of fuel rail , install a clear drain hose (clamp it ) and put other end in a gas can , disconnect the hood lamp wire and loosle connect to the fuel pump prime ,
if you are sucking air youll see the bubbles pump through the clear hose

Interesting theory, You think it applies here?

What I am experiencing is: When the pump primes, fuel pressure immediately builds up and then falls off. Just as a test I went to the fuel station and filled up and the pressure held. I wonder if the pump needs to be submerged into order to stop it from bleeding off.

 

[pacecarta]

then why didnt you say that in the first place

in the future posting as much info about your problem will net you a better answer ,


but yes what i posted still applies , pump should hold regarless of fuel level unless it sucking up air ,

 

[Mad_Trbo]

then why didnt you say that in the first place

in the future posting as much info about your problem will net you a better answer ,


but yes what i posted still applies , pump should hold regarless of fuel level unless it sucking up air ,

Thanks, do you think this can be fixed. In other words does it have to do with the way the pump was mounted? I did replace the stock unit with a walbro unit.

 

[pacecarta]

the check valve is in the top of the pump , if it doesnt do it all the time i think your issue is air in the lines

for fuel pressure to drop off sudden
either
the injectors are leaking past tip into intake which you would notice as smoke at startup
or / the check valve in the pump is bad and would require chaning the pump
or/ the fuel pressure regulator is bad and wont hold pressure
or/ the lines between pump and fuelpressure regulator have a leak
leaks could be
injector rail leak at top of injector
rusted feed line
oring missing/damaged at connectoins to fuel rail/ fpr or fuel pump
rubber hoses above tank/axle leaking
rubber hose in tank at pump leaking
you say it doesnt do it when tank has fuel so i would discount there being any leks or issue with FPR ,

air in lines is what i think you have, try keeping gas in the car

if the rubber lines in the fuel sytem arent swelling up it doesnt take a lot of fuel to drop the pressure from 45 to zero ,

 

[bison]

Be sure that the piece of hose from the pump to sender isnt loose. Ive seen these loosen up on several cars and cause a lot of pressure problems when volume and pressure is needed. It could also leak backward if its really loose causing a zero psi turnover after you shut the car off.

 

[Mad_Trbo]

the check valve is in the top of the pump , if it doesnt do it all the time i think your issue is air in the lines

for fuel pressure to drop off sudden
either
the injectors are leaking past tip into intake which you would notice as smoke at startup
or / the check valve in the pump is bad and would require chaning the pump
or/ the fuel pressure regulator is bad and wont hold pressure
or/ the lines between pump and fuelpressure regulator have a leak
leaks could be
injector rail leak at top of injector
rusted feed line
oring missing/damaged at connectoins to fuel rail/ fpr or fuel pump
rubber hoses above tank/axle leaking
rubber hose in tank at pump leaking
you say it doesnt do it when tank has fuel so i would discount there being any leks or issue with FPR ,

air in lines is what i think you have, try keeping gas in the car

if the rubber lines in the fuel sytem arent swelling up it doesnt take a lot of fuel to drop the pressure from 45 to zero ,

Thanks for the analysis, I am thinking of changing out the pump. I have read the pump will work into the high 10's but alot of people on the board say no way. Kind of confusing for me, all I really want is a sick street car no track time.