Not holding fuel pressure.

[fastmonkeywheel]

I haven't started my engine yet, but I wanted to check my fuel lines so I put about 5 gal of fuel in an empty tank and cycled the key to RUN/OFF to prime the system. Nothing was leaking from the fuel lines. Fuel pressure got up to 43 psi but as soon as the fuel pump turned off the pressure started dropping all the way to 0, not really fast but it did. I pulled the plugs and smelled them, I didn't smell fuel on them and they didn't apear to be wet so I doubt I have a fuel injector stuck open. I removed the return line and their was a little fuel in it but not alot.

I thought maybe the regulator might be bad, but if it was wouldn't there be a lot more fuel in the return line? Could the pump not be holding the pressure when turned off? It's an inline pump from a Merkur. I had to plumb the main line myself. I ran 5/16" line from the tank to the pump, then pump to a GM filter then to the fuel rails. The main line is tapped from the stock location which is down at the bottom but the return line is above the fuel level right now, but that shouldn't cause a problem I don't think.

 

[Red_LX]

I had the same problem when I first tried to crank my engine, turned out the regulator I had on the engine had a ruptured diaphragm so it wouldn't hold pressure. What I was told to do was pull the vacuum line off the regulator and smell it to see if it had gas in it, if it did that meant the diaphragm was ruptured. Also I was told there was some kinda valve in the pump that was supposed to keep pressure from bleeding off- don't know much about that though. The fuel pressure on my car bleeds down to zero after an hour or two, and I can't find any leaks, and I think my old engine did that too. I figured it was normal

 

[fastmonkeywheel]

So in order to start your car you have to cycle the fuel pump first? Or does it start right up?

I'm going to be getting an adjustable fuel pressure regulator anyways, I hope that's what it is. If not it doesn't seem to be causing your much concern so I guess I could live with it.

 

[Red_LX]

Nah it starts right up. The pump kicks on for a couple seconds when you first turn the key to start and that builds pressure in the system.

However, in your case I figure if the pressure is dropping off fast enough that you can see it dropping on a gauge, there's probably some sort of problem, though I couldn't tell you what exactly.

 

[99blkcobravert]

I agree with RedLX about the fuel pressure regulator; best place to start. When you replace it, test the pressure drop off.

 

[fastmonkeywheel]

Will do, thanks guys.

 

[rd]

I had this on a Windstar, it would start after two or three cranks.

I changed the regulator to no effect.

Turns out the check valve in the fuel pump failed. Changing the fuel pump immediately fixed it.

If the vehicle is running or the pump is on, you can clamp the rubber line from the pump to the fuel rail and shut it off. If it hold pressure then, it is the pump check valve.

 

[fastmonkeywheel]

I'll try that, I'm hoping to start it up today for the first time.