Fuel pressure drops when engine is off

DOMYN84

MEMBER
2005 SUBARU FORESTER
2.5L
4 CYL
4WD
AUTOMATIC
177,000 MILES

Hello, I have a question about my vehicle listed above. Car runs oddly, it feels like engine wants to shut off sometimes, sometimes it won’t respond when I step on a gas pedal for a couple of seconds. It feels like engine power is decreased and gas mileage is dropped. I replaced air filter, spark plugs, cleaned MAF sensor, without any change. There is no check engine light on, so I decided to measure fuel pressure. First, I measured with fuel pressure regulator vacuum hose connected to intake manifold. It was 36 psi, which is 2 psi higher than normal (30-34psi). Then, I measured with fuel pressure regulator vacuum hose disconnected, and it was 46psi, normal(41-46psi). So overall fuel pressure is little bit higher than normal. Another thing I noticed is that when I shut off the engine fuel pressure drops rapidly to 5 psi, and I know it is not good. There are no obvious fuel leaks anywhere. So, what can it be? Can fuel pressure regulator be bad?

Sunday, September 29th, 2019 AT 10:21 AM

3 Replies

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Welcome to 2CarPros.

The fuel pressure seems good. However, it shouldn't drop off that fast. Since the engine isn't running as it should fuel mileage has dropped, it almost seems as if there is a stuck injector or at least a leaking injector.

Do me a favor. Here is a link that explains how to check injectors. Read through it and see if everything seems to be working properly on the vehicle.

Also, the reason I am saying injector for the pressure drop is because if the issue was before the engine (pump, filter, and so on) it wouldn't be causing decreased MPG. Try this and let me know what you find.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

The injectors aren't real easy to access. I attached a pic of how they are located on one side.

Let me know what you find.

Joe

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Sunday, September 29th, 2019 AT 7:32 PM

DOMYN84

MEMBER
2 POSTS

Hi, thank you for your response Joe. Finally, I’ve tested injectors according to instructions you provided. It seems like injectors are good. All power and resistance tests are okay. Then, I removed fuel rail with injectors and watched them while fuel system was under pressure, and no one of them was leaking. Spray patterns are all good enough. Additionally, I decided to stop fuel flow on the pipe from gas tank right after the pressure gauge by holding it with pliers. So I could check if the pressure isn’t dropping on its way to engine. The result was that it doesn’t hold pressure too. So what can it be? Fuel pump and filter are inside of a gas tank. Can fuel pressure be lost through fuel pump?

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Friday, October 4th, 2019 AT 8:28 PM

JACOBANDNICKOLAS