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Discussion Starter #1
Hi. I have a problem that requires a long drive to test.

After driving for about 1 hour, the car hesitates.

Symptoms, all after an hour and the car is good and warm..
Lack of power
Hesitates when under load
Idle ok
Pings when I let off the gas pedal

I have to pull of the highway (praying there's a big shoulder) and wait for 30 minutes. Then I can drive another 20 minutes before I have to pull over and wait for something to cool down. [What IS THAT something???!!!]
This problem is progressive. It used to only happen during hot summers, 80+ degrees. Now it's happening during winter too.

I've replaced / tested:
Coil pack
Spark plugs
Plug wires
Engine to battery ground wire
Battery to firewall ground wire
Battery to starter (red) wire
GE wires (4 on the block at the top) - sanded to make sure connection is good.
Intake Air Temperature sensor
No blockage in the exhaust pipe.

Anyone have any ideas? I've talked with my car mechanic friend who has many years of experience and he even went to auto tech school in the 80's. He can't figure it out either.

2.5x Engine in a 2003 Subaru.
 

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2009 Legacy
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787 Posts
@OhTwoCenCer No codes thrown when this happens?
This is the second time today I suggested to someone here measure the fuel pressure. Perhaps the pump is seizing up when it gets hot so puts out less pressure, maybe enough to idle but not enough to deal with load.
Certain cars use pumps that are cooled by gas. Some cars have issues when fuel gets low for that reason. Not that I'm suggesting you run with a full tank to alleviate the problem but just illustrating that pumps can cause intermittent issues when they overheat.

Please don't run out and get a new pump - this is just one thing to check. See if your mechanic friend can help you rig a fuel pressure gauge in temporarily. Then, when pulled over, check the pressure. If it isn't within spec, start looking at the pump.
 

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2018 FXT-T CVT / 2007 FXT 5MT
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1,450 Posts
Had these exact issues with a Nissan Frontier pickup. Drove great until it got good and hot then total power loss. After everything replaced my last resort was injectors and that resolved it. No idea what the injectors were doing that was causing it, but they are what fixed it.

Given you are pinging, I can almost guarantee you it's fuel...
 

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2018 FXT-T CVT / 2007 FXT 5MT
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Crankshaft on that truck, yeah. I replaced like...every dang sensor...I thought for sure it was a knock sensor or something putting it into limp mode. No idea what has happening to it...never threw a code but it was supercharged so the lack of power was the supercharger bypassing....so it may be different from the power loss you're experiencing. But...I'd strongly lean towards being fuel related and in that case there's not a ton of look at. Fuel pump, fuel filter, fuel injectors, fuel pressure regulator. Gotta be one of those.
 

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I have nearly the identical issue with 05 FXT. Will be replacing the pump to see if it resolves the issue. I've clocked at almost exactly 50 miles of driving at 75 mph it starts to shudder and can be made to go away by backing off the gas and mashing it a few times. Comes back after a few minutes. I'll report back if it fixes the problem.
 

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Discussion Starter #9
Still getting hesitation after 70+ mph on highway for an hour. Nothing else is wrong. Everything else works. This car has 300,000+ miles on it.

The following components are new on a newly rebuilt engine: MAP, TPS, IACSV, Air and Fuel filters, Wires, Plugs, Coil pack, Injectors, Crank- and cam-shaft position sensors, timing belt, wires to and from battery, ground points, fuel pump and in-tank filter.

I replaced the front fuel filter on tuesday afternoon. No joy.

Last night I was looking at the service manual which said there is a pressure control solenoid valve for the fuel tank. I've never replaced this. \

Maybe I should replace the pressure control solenoid valve, drain filter, drain valve and purge control solenoid valve?

Which of these 4 components would cause the car to hesitate after 55 miles on highway at 70+ mph?

There are no other symptoms or Check Engine Codes on this Subaru 2003 Forester X Automatic.

Thank you!
 

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2012 Forester 4 speed auto
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997 Posts
There is a good chance the fuel injectors are shorted. You might check them using an ohmmeter but the best test would be with an oscilloscope. However a ohmmeter will do if you know the specifications for your injectors. A little research can go a long way.
 

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2018 FXT-T CVT / 2007 FXT 5MT
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Long shot but has the car ever been in a wreck where there might have been some welding done where an electrical load could have fried something in the ECU where it gets some weird signals over time and might be pulling timing as a result over time? I've had that happen before.
 
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