2008 dyna 3.000 miles. runs on rear cylender only.swaped enjectors it the same runs on rear cyl only

check resistance on plug caps and compare , swop over and see if problem moves to other cyl !

Assuming that you have done a compression test and both cylinders have ample compression to run( adverage 150 psi) check that both plugs are actually sparking. If this is a fuel injected model check fuel pressure, check for voltage at both injectors on the common color wire to each. If all is good there you can swap the front injector to the rear(provided they are the same part-most are) and see if the dead cylinder moves with it. If it does the injector is bad.

Yes it sounds like its time for a tune-up plugs,wires,fuel filter and air filter

I kinda wonder if your rear jug plug wire is leaking & grounding it's self.

No the subarus run a long time especially if you change the oil and filter every 3,000 miles and say every 25,000 to 30,000 change the spark plugs and wires and every 30,000-40,000 change the fuel filter.Basically just do routine maintaining of the vehicle and its not uncommon for them to run 200,000 miles or more.

2008 Pontiac G5
2008: Base; 4 Cyl 2.2L; "GAS, FI, L61, VIN F" 2008: GT; 4 Cyl 2.4L; "GAS, FI, VIN B"



How to Replace a Fuel Filter
(DIY Complexity: Moderate / Time: 1.4 hours)

Parts:
1. Fuel Filter

Tools:
1. 3/8 in. Drive Ratchet
2. Hose Pincher
3. Flare Nut Wrench
4. Flat Head Screwdriver
5. Socket Set

Steps:
Step 1 Open the hood and locate the fuel filter. If the fuel filter is not in the engine compartment, follow the fuel line from the tank until the fuel filter is located.
o Tip: Safety Tip:Always wear safety glasses when working on your vehicle. Wear other personal protective equipment (PPE) when necessary, for example latex gloves or safety shoes.

Step 2 If the fuel filter has a clear case, inspect the filter element for dirt.

Step 3 If the fuel filter case is not see-through, remove it from the fuel line. Drain the fuel from the filter into a container and inspect the condition of the fuel.
o Tip: Caution: Before removing fuel lines or fuel related parts, make sure that the fuel pressure is relieved from the vehicle fuel system. To relieve the pressure in fuel injected systems, remove the fuel pump fuse and run the engine.

Step 4 Install the new fuel filter making sure that the flow is in the correct direction. The arrow on the fuel filter is the direction of flow from the tank to the engine.

Step 5 Secure the lines back onto the fuel filter. If applicable, reinstall the fuel pump fuse.

Step 6 Start the engine and check for fuel leaks.

Step 7 Test drive the vehicle to check for a rough running engine, hesitation, or lack of power.

Hope help with this.

check your owners manuel..if you have none than purchase one.
I would say leave them alone .

run engine codes, had same issue once before it was bad computer good luck