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Fuel cuts off once warm?

Tiny
KAMORLE
  • MEMBER
  • 2000 MAZDA MPV
  • 2.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
My old vehicle listed above starts and runs great but once it warms up the fuel pressure drops off and it almost stalls (or will stall) if I press the accelerator. I've replaced the fuel pump/filter unit to no avail. I've replaced the throttle control sensor and fuel pressure regulator sensor without any change. Where should I look next?
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Saturday, August 17th, 2024 AT 9:56 AM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
Hi,

How low does the fuel pressure get? It sounds like you have replaced a lot already. Are you certain it is a fuel pressure related issue?

Also, when it stalls warm, does it start right back up for you?

Let me know.

Joe
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Saturday, August 17th, 2024 AT 7:15 PM
Tiny
KAMORLE
  • MEMBER
  • 5 POSTS
I don't have a fuel pressure tester so I'm witnessing it on the return line before the tank as the gas pours into a jar, when cold there is a lot of gas moving through the system when warm almost nothing. Yes, when it stalls (only happens if I keep the accelerator pinned) it starts right back up and drives normally for a minute or so.
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Saturday, August 17th, 2024 AT 7:35 PM
Tiny
KAMORLE
  • MEMBER
  • 5 POSTS
Cold
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Saturday, August 17th, 2024 AT 7:38 PM
Tiny
KAMORLE
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  • 5 POSTS
Warm
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Saturday, August 17th, 2024 AT 7:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
Hi,

I see what you are referring to. What I suggest is this. Since the pressure drops when the engine is warm, compare the voltage at the pump under cold conditions and then again when it is warm. Just be careful not to cause any sparks.

Let me know if there is a difference. Other than trying this, we need to get a fuel pressure gauge. Most parts stores will lend one to you.

Also, let me know if there was no change when you replaced the pump. In other words, is it doing the same thing as before?

One other thought. Switch the fuel pump relay with a different one in the box having the same part number. See if that changes things at all.

Let me know.

Joe

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Saturday, August 17th, 2024 AT 8:02 PM
Tiny
KAMORLE
  • MEMBER
  • 5 POSTS
I've actually tried running the pump directly off a separate 12v battery to no change just to rule out any electrical issue. At this point I'm experimenting with the fuel regulator attached to the fuel rail.
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Saturday, August 17th, 2024 AT 8:07 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
Hi,

If the pump is making constant pressure, the only thing left would be the regulator. How are you checking it?

Joe
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Sunday, August 18th, 2024 AT 7:30 PM

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