Will not stay running?

2003 MERCURY GRAND MARQUIS
140,000 MILES • 4.6L • V6 • 2WD • AUTOMATIC
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TRMISOK
  • MEMBER
  • 5 POSTS
No start unless you put pedal on the floor, and it starts but shuts off right away. But sometimes it will stay running if you keep RPMs way up. If you let off the pedal, it shuts off. But it does not start most of the time.
Fuel pressure is 35 to 45 PSI.
put in new plugs.
put in new IAC.
cleaned MAF (getting a signal from MAF) forgot reading.

Oh, when it starts, it will puff out black smoke from exhaust.
Mar 13, 2024 at 2:20 PM
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JACOBANDNICKOLAS
  • CERTIFIED EXPERT
  • 110,175 POSTS
Hi,

The idea that you need to press the throttle to the floor tells me it is flooding. By pressing the throttle to the floor, it shuts off the fuel injectors to clear a flooded engine. Additionally, the black smoke indicates the same thing, too much fuel.

Since the fuel pressure is within specification, I need you to check fuel pressure drop off when the key is turned off. This way we can determine if you have leaking fuel injectors causing the engine to flood.

I attached the directions below for testing fuel pressure drop off (leak down). Also, there is a fuel rail pressure sensor that may be causing issues. Have you scanned for diagnostic trouble codes?

Let me know.

Joe

See pic below.
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Mar 13, 2024 at 7:24 PM