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Man! This is tough. So the other day I'm driving my FJ Cruiser and the vehicle starts to hiccup and won't accelerate. I noticed right away that my battery voltage is depleting quickly. After about a mile of driving my truck completely dies. I get the truck towed and I replace both the alternator and the battery. I start the truck and let it idol for a couple of minutes. When I jump in the vehicle to take it for a test drive the truck begins losing power like before. The voltage gage needle begins to lower again and the my FJ acts like it wants to shut down again. So I turned off my truck, and disconnected the battery.Shaking my head, can anyone help please. What is this?
 

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Something is causing it to stall out... and when the rpm's drop, the alternator loses it's ability to charge.

How's everything else?
Air filter?
Plugs?
Bad gas?
 

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How many miles on your FJ? Do you have a way to check the fuel pressure? DEWFPO
 

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Check the 7.5A ALT fuse in the engine bay ... if this fuse is open, the alternator will not 'turn on' and won't output any current.

If the voltmeter indicates slowly dropping battery voltage while the engine is running, obviously the alternator is not providing any charging current.
 

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Discussion Starter #5
Thank you my fellow Cruisers. My suspicions are beginning to lie in the electrical system @FJtest Thank you for your input I'll begin my search in the engine bay fuse box. And then check the fuel pressure. @DEWFPO Thank you for your time in supporting me 🙏
 

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All the symptoms you describe point to an electrical system problem. The fuel pump pressure will naturally drop as battery voltage droops below 10V.

1. Check the 7.5A ALT fuse.
2. Using a good-quality digital voltmeter, measure the system voltage directly across the battery terminals with the engine off and no other electrical loads (radio off, all doors closed, etc.).
3. Start the engine, bring the engine speed up to 2,000 RPM and again measure the system voltage.

Let us know what the voltage measurements were per steps #2 and #3.

Because of the quick-disconnect fittings Toyota uses in the fuel lines, making a fuel pressure measurement is difficult unless you have special service tools, so checking the electrical system first is much quicker and easier.
 
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