fuel pressure goes to zero as soon as I shut it off

[gmmaft]

Hi, I did a search but I really didnt find what I needed. I had to replace my fuel system because the car sat for too many years with old fuel in it. so I replaced the entire fuel system.and had the rails cleaned. right now im just waiting on my regulator. so the stock one is still in. when I start the car it has a constant flow of pressure and I cant find any leaks but I can smell a very small gas oder. but as soon as I shut the engine off the pressure goes to zero right away. the only real changes I made was to the return line. I made the return 3/8 to match the feed.
so here is what I did
feed 3/8 alum hard line from the tank sender to the rail.
return 3/8 alum hard line from the rail to the tank.
all 6an fittings (even on the sender) no rubber hoses at all
aeromotive 10 inline filter
aeromotive stealth 340 pump
hotwire
fuel rail pressure gauge

the pressure is constant at 23 psi (only because I didnt get the regulator yet. waiting on ups) I know its too low. but my concern is why is the fuel pressure gone as soon as I shut the engine off?
what did I do wrong?
Is it because I used a 3/8 return line? is it too wide?
I thought using a wider return line would make my pump work a little easier.
any help would be awesome because I really dont know what im doing.

 

[jpratt]

My guess would be regulator is bad. That might account for low pressure and immediate pressure drop.

 

[gmmaft]

My guess would be regulator is bad. That might account for low pressure and immediate pressure drop.

but it was holding pressure before I changed these fuel lines. I think the regulator is ok but im replacing it with an adjustable regulator. those 6an fittings make me nervous tho

 

[pacecarta]

doesnt take much leakage to drop pressure when the system doesnt have old ballooning hoses


since you say the reg worked and held before , leaks in return side wouldnt effect presure than you have a leak in the feed side.
it could be at the hose inside the tank, bad checkvalve at the pump
but since you say you smell fuel you have a leak in the feed side , at line connections , oring at the regulator , orings at injectors, connection at the sender
find the leak and fix it

 

[gmmaft]

doesnt take much leakage to drop pressure when the system doesnt have old ballooning hoses


since you say the reg worked and held before , leaks in return side wouldnt effect presure than you have a leak in the feed side.
it could be at the hose inside the tank, bad checkvalve at the pump
but since you say you smell fuel you have a leak in the feed side , at line connections , oring at the regulator , orings at injectors, connection at the sender
find the leak and fix it

Im smelling it in the rear so im thinking those 6an fittings that I installed onto the sending unit might be leaking. but I dont see anything dripping from anywhere. something told me not to use those fancy fittings. I guess im dropping the tank again in the morning
thanks for your help

 

[Blazer406]

Some times the check can go out in the FP and it won't hold pressure...... not a huge deal except it looses pressure after you kill the pump.

I've seen a brand new 340 Walbro do this.

 

[gmmaft]

Some times the check can go out in the FP and it won't hold pressure...... not a huge deal except it looses pressure after you kill the pump.

I've seen a brand new 340 Walbro do this.

wow, I hope not because I just bought that pump last saturday

 

[Blazer406]

wow, I hope not because I just bought that pump last saturday

It doesn't diminish the pumping capacity of the pump..... but it just releases the line pressure back into the tank when you shut the pump off.....

 

[gmmaft]

It doesn't diminish the pumping capacity of the pump..... but it just releases the line pressure back into the tank when you shut the pump off.....

but I am smelling it at the tank and sender area. im thinking that I made a big mistake mounting 6an female fittings on the sending unit because I dont think it sealed properly. im thinking about taking out the sender again and taking it to a welder and having those an fittings welded or soldered onto the sender pipes to seal it up. I should have used steel braded hoses from the sender to the hard lines. but I took the advice of the speed shop.

 

[Pronto]

The Racetronix unit with AN fittings are welding on. Did you flairless compression AN fittings?

 

[gmmaft]

The Racetronix unit with AN fittings are welding on. Did you flairless compression AN fittings?

yes, it was my first time using those an compression fittings. I guess I need more practice. I just wound up having 6an fittings welded on to my sending unit. that solved the pressure drop issue.

 

[Pronto]

In your first post you mention using al hard line and no rubber hose. I would not rely on that. The al will flex some over time and it will crack. You need a stress breaker in there to let the tank move slightly and not work the metal line. You can make small stubs with AN flares on one side and a bubble on the other to go over f.i. hose, that's what I'm doing. Racetronix is AN8 and 6 so I'll need female to male reducers to match the stock size lines.

 

[gmmaft]

In your first post you mention using al hard line and no rubber hose. I would not rely on that. The al will flex some over time and it will crack. You need a stress breaker in there to let the tank move slightly and not work the metal line. You can make small stubs with AN flares on one side and a bubble on the other to go over f.i. hose, that's what I'm doing. Racetronix is AN8 and 6 so I'll need female to male reducers to match the stock size lines.

ok, I will do it like you are doing yours. im still learning these cars. thanks for the advice.

 

[Pronto]

You can just take a section out of the al line and splice in some f.i. hose. Should be easy enough.

 

[gmmaft]

You can just take a section out of the al line and splice in some f.i. hose. Should be easy enough.

yes I just broke it up in 2 spots and pus some of that really strong fuel hose that they sell at the speed shop. I forget what its called but it looks really strong. now im just waiting for ups to frop off my fpr today. any idea what I should set the fuel pressure at? my car is pretty much stock.

 

[groumoutis]

43 with the vac line off.

 

[gmmaft]

43 with the vac line off.

thanks