Q: Car won't start after fuel pump installation 2004 Subaru WRX/STi Hybrid

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After I installed a new 320 AEM fuel pump, the car won't start properly. The car WILL start say after leaving it overnight or, after it's been completely off for over an hour. When the car does start, it feels like it loses power or combustion. I have to rev it up to 300 rpms for half a minute and the under power symptom stops. It didn't do this with the stock Walbro pump. Though, I did notice the fuel pump sock is quite smaller, I've read other people replacing it with this AEM pump without issues before. I need to install the fuel injectors too, as recommended by my tune guy before getting it Protuned this Wednesday.

Please help!

My car has 155000 miles.
My car has a manual transmission.

If the hard starting issue began immediately after the pump install, a possibility is the fuel delivery (pressure and volume) characteristics of the new pump are far enough off stock (or your just prior pump), that the engine either floods, or delivery is inadequate (you mention a smaller pick up), at least during start up. Another possibility is a defective pump or an installation issue, overlooked restriction in the lines and so forth. if you request a no/hard starting - engine diagnostic the responding certified mechanic will take a look at what you have and pinpoint the cause. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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