I recently changed fuel pumps and when I was testing pressure I noticed that the pressure went to zero as soon as I turned the key off. Is this normal? I thought that it kept a little pressure for a while. The truck runs all right, just have a p1178. Pressure is 36psi

 

Fuel pressure regulator or leaking injector(s).

 

2x on what ih said.....the vaccum hose to the regulator could be rotten (personal experience)

 

I checked the fuel regulator with a vacuum pump and fuel pressure gauge, the vacuum hose looks good, put on a new maf

 

I have a similar issue and not normal.


Not sure if this is possible or not but can the fuel leak back into the tank through the supply side line if the pump is bad allowing pressure to be released? If return line pressure should be held by the FPR.

 

I pulled the fuel pump and resealed the gasket on the top of the tank. The code went away. Not sure it will stay away.

 

I know this original post is slightly dated but it ties in to my issue.

I've been having some start up issues of late, as in it always takes two to three cranks to get started and when it does its often hesitant. Now my starter, plugs, cables, coil assby, alternator, air filter, etc....are all like nearly new. Less than 5 miles on all of it. So im leaning rowards fuel system.

Also, I've already replaced the fuel filter, fp regulator, and all rubber lines around the manifold including vacuum. Also the hard plastic lines and the canister are new.

Oh BTW, also had the injectors sent out and cleaned, got back a great report, all were spot on and the same outputs at peak of spec. Can't recall offhand the numbers but they're good.

Heres the ahhhh moment, upon recent fill up I apparently went past shut off and observed fuel pouring from top of the tank.
Quite a bit in steady flow. Not cool at all.

I've pressure tested the fuel and get:
Zero when cold.
35 firm at 2 clicks of the key
Drop to 30 after about 10 seconds with key still in 2 click mode
Zero after a minute.

Now before I go tearing into the tank access I'm wondering.....
Is this leaking fuel scenario likely the source of my pressure drop?
It's all a closed system right?
Lastly, any pointers on what I'm likely to encounter as the most common causes of said leak?

Judging from drawings I'm guessing it's the tank seal, or there's a line from the tank to the filler neck.

Anything else I might overlook that I need to see before I start removing things? This is one area I'm not familiar with firsthand.

For reference it's a 99 D1 N.A..

 

the leaking fuel is likely coming from a rotten fuelfiller hose, vent hose , or fuel pump sealing ring(gasket) on top of the tank........but none of that will effect the fuel pressure since the tank is not pressurized to give you fuel pressure....the pump pushes fuel out of the tank and the regulator is supposed to keep it at around the mid 30's for pressure. Most pump assy's have an anti drain back feature to hold pressure in the supply line (for a while)....I'd replace the pump if it hasn't already been done, and use a new seal ring while you're at it..and while your ther you'll get a better idea of where the leak is coming from