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I haven't got an answer for you but have a similar problem. I'll outline my symptoms, and what I've done so far. Maybe it'll help, or if someone will suggest a line of attack for me, might also help you.
My car is also a 1996 Grand Marquis, with the 4.6L V8 engine.
I don't drive it everyday, so when it sits for a time, 4-5 days, it will be a hard start, whether it's 100 degrees out or 10 below. It fires off, but only runs a second, then stalls out. Sometimes i have to do this 3 or 4 times before it runs properly, and then it's fine all day for many starts. No issues stalling during the day, and runs perfectly otherwise.
I have a fuel injection pressure gauge, and used that to get these pressures, while referring to the Haynes Repair Manual.
With the engine at idle, Fuel Pressure Regulator vacuum line attached - 30 psi - Haynes manual says 30-45 psi is normal, but 30 is right at the bottom of the range.
Disconnecting the F.P.R. vacuum line - 40 psi - Haynes manual says 40-50 psi is normal.
Engine draws 20" of vacuum at the F.P.R..
Reconnecting the vacuum line, If i hold the rpms up at 2000+ rpm the pressure spikes to 38-40 psi, but settles back on it's own to 30 psi while still running at 2000 rpms.
I shut the engine down, and after 10 minutes, it still held the 30 psi in the fuel system. Also in spec with the Haynes manual.
After relieving the fuel pressure, and then with the Key on, and not starting the engine - it shows 37 psi in the fuel system. Haynes manual shows 35-45 psi is the norm.
So, now am wondering what the best place to start is? My manual said to pinch off the fuel return line, and see how that affected the fuel pressure. For example, if it doesn't affect pressure, then likely the fuel pump is bad. If it spikes up sharply, then it's likely the fuel pressure regulator. I haven't been able to do that yet, (will tomorrow) i need to rig a flexible rubber hose into the return line somewhere. The flexible one, seems to still be rigid enough that i can't pinch it closed.
Given all that, if i rule out the fuel pump and pressure regulator. What else could it be? There's never a puddle of gas where i park, so it can't be leaking out.
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∙ 12y ago
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