Car has trouble starting

Hi,

There are several things which can cause this. First, there could be a low fuel pressure issue. Also, the engine coolant temperature sensor can be causing a problem. The engine coolant temperature information are transmitted to the ECM to make fuel injection, ignition timing, purge control solenoid valve and other controls. If the sensor isn't indicating the correct temp, the air / fuel mixture may be too lean for it to start in extreme cold. Also, if it hasn't been tuned up in a long time, worn plugs can cause it as well as lower engine compression.

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Okay, here is what I suggest. If you have a live data scanner (I noted beginner mechanic), check the ECT (engine coolant temp sensor) signal to confirm it is telling the computer the correct temperature.

Next, if the ECT is correct, then I would confirm fuel pressure isn't weak. Here is a link that explains how to test it:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Here are the directions specific to your vehicle. The specs are included in the directions and picture 1 correlates with the directions.

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2010 Subaru Impreza F4-2.5L SOHC
Component Tests and General Diagnostics
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Testing and Inspection Component Tests and General Diagnostics
COMPONENT TESTS AND GENERAL DIAGNOSTICS
Fuel Pressure

INSPECTION

CAUTION:
Before removing the fuel pressure gauge, release the fuel pressure.
Be careful not to spill fuel.
Catch the fuel from hoses using a container or cloth.

NOTE:
Check or replace the fuel pump and fuel delivery line if the fuel pressure is out of the standard.

1) Release the fuel pressure.
2) Open the fuel filler lid and remove the fuel filler cap.
3) Disconnect the fuel delivery hose from the fuel damper, and connect the fuel pressure gauge.

pic 1

4) Start the engine.
5) Measure the fuel pressure after warming up the engine.

NOTE:
The fuel pressure gauge registers 10 to 20 kPa (0.1 to 0.2 kg/cm2, 1 to 3 psi) higher than standard values during high-altitude operations.

Fuel pressure:
Standard
339.5 - 360.5 kPa (3.5 - 3.7 kg/cm2, 49 - 52 psi)

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Let me know when the last tune up was. Also, you may want to remove a spark plug to check condition. Here are the directions for removal and replacement. I have to be honest, if it has been awhile, I would just replace them, but that is up to you.

The pics correlate with these directions.

2010 Subaru Impreza F4-2.5L SOHC
Removal and Replacement
Vehicle Powertrain Management Ignition System Spark Plug Service and Repair Removal and Replacement
REMOVAL AND REPLACEMENT
Spark Plug

REMOVAL

Spark plug:
Refer to "SPECIFICATION" for the spark plug.

1. RH SIDE
1. Disconnect the ground cable from the battery.

pic 2

2. Remove the air cleaner case.
3. Remove the spark plug cords by pulling the boot. (Do not pull the cord itself.)

pic 3

4. Remove the spark plug with a spark plug socket.

pic 4

2. LH SIDE
1. Remove the battery.
2. Remove the spark plug cords by pulling the boot. (Do not pull the cord itself.)

pic 5

3. Remove the spark plug with a spark plug socket.

pic 6

INSTALLATION

1. RH SIDE
Install in the reverse order of removal.

Tightening torque: 21 N.m (2.1 kgf.m, 15.5 ft.lb)

2. LH SIDE
Install in the reverse order of removal.

Tightening torque: 21 N.m (2.1 kgf.m, 15.5 ft.lb)

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If you find the ECT is faulty, here are the directions for replacement.

2010 Subaru Impreza F4-2.5L SOHC
Removal and Replacement
Vehicle Powertrain Management Sensors and Switches - Powertrain Management Sensors and Switches - Computers and Control Systems Coolant Temperature Sensor/Switch (For Computer) Service and Repair Removal and Replacement
REMOVAL AND REPLACEMENT
Engine Coolant Temperature Sensor

REMOVAL

1. Disconnect the ground cable from battery.

pic 7

2. Remove the generator.
3. Drain engine coolant.
4. Disconnect the connectors from the engine coolant temperature sensor.

pic 8

5. Remove the engine coolant temperature sensor.

INSTALLATION

Install in the reverse order of removal.

NOTE: Use a new gasket.

Tightening torque: 18 N.m (1.8 kgf.m, 13.3 ft.lb)

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Let me know if any of this helps or if you have other questions. I will watch for your reply.

Joe