FI Fuel Pressure in the Morning?

[RustyWa]

From another post....about testing fuel pressure and how long pressure should hold in the system.

DD says, "I think that if you're over 20 PSI at the end of a half-hour, you're fine."

After shutting my car off, my pressure will drop from 28psi to 19psi in about 45 minutes. If I wait about 6 hours, the pressure gauge will show 0 psi. This can't be correct and has to be the reason my car has started to stall 3 seconds after starting. It's only a problem after the car has sit all day, no problem when there is pressure in the system.

I've disconnected the CSV and isolated the injectors on the passenger side, visually check the injectors on the drivers side (no leaks) and I still get the same symptoms.

[Will98D]

the pressure drop can come from: leakdown through the injectors (including the cold start valve), leaking past the fuel pressure regulator, and leaking back through the check valve in the pump. You have to isolate each one-by-one to determine what it is. If it's the check valve in the pump, you could probably retrofit a BMW kit that they have cheap (< $5 from the dealer) that is designed to address the same problem on the 735 series from the late 80s - early 90s. I bought two, one for my 535, and a spare for either the 535 or the 914. It comes with the check valve, a 1' piece of HP fuel hose already attached, and two hose clamps. If that's the problem let me know and I'll try to post the p/n.

[Dave at Pelican Parts]

Eric, it's not supposed to hold pressure all day! Leaking down to 0 after 6 hours is not a problem. If you think low fuel pressure is your car's starting problem, turn the key to "on" and listen for the fuel pump. It'll "buzz" for about 1.5 seconds and stop. Turn the key to "off" then back to "on" to get another buzz from the pump. Do that about 3 or 4 times, then start the car.

The fuel system pressure is supposed to bleed down to 0 over some period of time. That's why the pump runs for that 1.5 seconds when you first turn the key to "on".

If you've got an L-jet car (1.8 or a 912E) then you can't run the pump that way.

--DD

[pbanders]

If the car sits long enough, you'll end up with 0 psig in the fuel loop. I'm not sure I follow why you think this is the reason your car stalls from a cold start? Are you suspecting that the fuel is pooling at the intake ports?

I'll put a gauge on it, but I'm 99% certain that the pressure in my fuel loop before I turn the key in the morning is zero. When I turn the key, the ECU runs the fuel pump for 1.5 seconds to pressurize the line, so I'm not too concerned about the pressure prior to that point.

Maintaining pressurization in the loop after the car is warm and has been stopped for a while prevents vaporization of fuel in the fuel loop, improving hot starting.

(edited after Rusty pointed out it's 1.5 seconds that the pump runs - you'd think I'd know this )

[RustyWa]

The pump does run for the 1.5 seconds and immeditly goes to 29psi. I've tried to cycle it a few times to see if that makes a starting difference but it does not.

It's a new problem to the car. Before, no matter how long the car sat, a day week or month, I would just have to 'pop' the ignition and the car would start and idle perfectly. Now the car will die after 3 seconds of running. When I 'pop' the ignition a second time, the cars starts right up again but after 3 seconds lugs a little then is fine after that. Just seemed peculiar to me.

"Are you suspecting that the fuel is pooling at the intake ports?"

I'm not suspecting anything....that's the problem. If you say the 0 psi after 6 hours is normal, I need another reason. It's just a little nagging thing. From the other posts I've read recently about the piston rings problem and Cary's little hole....I guess I shouldn't complain!

[Will98D]

maybe your cold start injector is getting dirty, or some other reason the fuel mixture goes a little lean just after startup, and after a few tries it warms things up just enough to run on the leaner mixture.

[pbanders]

It's unlikely it's the CSV. The thermoswitch doesn't activate the CSV during cranking until the temperature is 32 deg. F or below. There are so many reasons this might be happening I could barely name them. I'd suggest checking all the basics first: valve adjustment, timing and dwell, spark plug gap, idle mixture CO, plus looking at the condition of all vac hoses and ignition parts.

[Kevin Powers]

rusty, after springing for the paint job your car is just reminding you that the money flow is similar to the spill gates on grand coulee dam.