Have you monitored your vvt solenoids? (If your engine has them)

 

2003 Subaru Forester - Variable Timing Solenoid

2003 Subaru Forester
(from O'Rielly)

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Variable Valve Timing (VVT) Solenoid
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Variable Valve Timing (VVT) Camshaft Sensor

 

Yes it is typically called the VVT solenoid. The only reason I ask if because they can cause misfires by causing incorrect timing between both camshafts. Because they are electrical they can start going bad when the engine if fully up to temp, but operate fine at cold temps.

You can use Free SSM software or a good quality scan tool to view the intake and exhaust timing angle. I'm not familiar with your engine so I'm not entirely sure if both your intake and exhaust came even have variable valve timing. If you have the ability to view it I think it would be a good idea to rule out.

That said what codes are you getting? You've put a decent amount of parts into it but without codes or at least live data analysis during the drive it is hard to offer any help. Chances are you would see something wrong with live data when you are experiencing the issue.

 

Does it have VVT? Could depend on the engine, although I'm fairly sure none had it in 2003. In any event, if the engine in question is a 2003 normally-aspirated 2.5, then the answer is no.

Is this a manual or automatic transmission?

 

automatic. And there's no vvt specifically. But there is a camshaft position sensor and crankshaft position sensor.

 

Could it be fuel related?

The generation of vehicle you have has a known problem with a metal cap on the fuel filter cracking and the fuel then leaks out a seal lowering the fuel pressure.

The fuel pump is located in the tank and can be accessed by removing the rear seat.

The other possibility may be a clogged fuel filter restricting fuel after a period of use. This seems like a “long shot” but it is quick and easy to check and cheap to replace.

Seagrass

 

In the Forester the fuel pump is accessed from behind the rear seat under the sub floor. Like the Imprezas. Fold the seat back down, remove the sub floor and the access cover is the right side cover. The left side is the second level sensor and transfer.

Any codes on the car's computers? Has any one checked for restrictions in the catalytic converter? Is the engine temp getting high?

 

I have replaced the in-tank fuel pump before. I remember the seal between the metal plate holding the fuel pipes to the pump and in-tank filter. I did not replace the seals. Sometimes the inside of the car smells like fuel. The pressure problems that could be caused by a faulty seal could be related to driving after a period of time.

I don't have codes. No restrictions. Engine temp normal.

It seems to be caused by an electrical component failing due to heat, or a problem with pressure somewhere after a period of time, especially in warm weather.

 

Please help!

 

The car needs to be examined when exhibiting the symptoms.
One possiblility is a fuel issue. The pressure drops after an hour of operation. There is enough fuel flow/pressure to support idle, but not enough to make power. Since you have replaced the pump, we'll look beyond a bad pump.
A bad charcoal canister will prevent proper fuel flow after a while as a vacuum is created in the tank. (when you open the gas cap, does it ever release a vacuum - hear a 'whoosh' of air?). After stopping for 30 minutes, the pressure in the tank equalizes to ambient and fuel can flow again.
Contaminants in the tank (rust, sand, etc) can accumulate on the pump inlet screen (I'll guess it has one) and inhibit fuel flow, but after shutting down for 30 minutes, the sediment settles off the screen and allows fuel to flow again.
Check the fuel pressure when the car stops running.