98 mitsubishi mirage misfire or fuel prob

Cylinder not firing
Check plugs

There is a cylnder coil for each cylinder prob failed
Check obd code

Other likely causes are:
Spark Plugs and Wires
Fuel Injectors
Internal Engine Problems such as Low Compression, etc.
Less Common Causes
Faulty Computer
Coil or Coil Packs
Crank or Cam sensors or reluctor wheels
Faulty O2 (Oxygen) Sensors

misfires are also cause from faulty injectors Check/replace the injector as the tip may be partially blocked.

After you changed ONLY spark plug wires?

I would say you failed to mark them before
you took them off & make a diagram or have
reference material & you put the wires on wrong
& now you have cylinder misfires & unburnt fuel
out the exhaust

chek plug cables first of all

You may want to try changing the coil pack rubber boots. Especially if your have recently had an alternator failure or battery failure. The coil packs themselves are probably good but I've changed my boots at least 4 times now. I have a 2000 Mirage DE with 198,000 miles. Runs great.

Swapping coils between cylinders is a better solution than replacing them. This way if the misfire follows the coil you know the coil is bad. Lack of power under load usually suggest fuel starvation to me. I would change the fuel filter and then road test the car. Also if you had just filled up the tank when the misfires started, maybe you got a bad tank of gas. Sometimes right after a rain water gets churned up and gets into the pump, and consequently your fuel tank.

very unlikely to be fuel filter. misfires on petrol engines are usual down to the ignition system,possibly Plugs or leads if fitted. plugs should be replaced every 40,000 miles, not an expensive item either.

head gasket

Check the voltage with someone cranking the engine. The fuel pump relay is incorperated in the FI relay located under right center of dash. It is a metal relay usually bolted to the floor near the ecm. Double check all the fuses inside and out

the p0171 code is for a fuel system lean code......possible causes are a cracked exhaust manifold.....bad o2 sensor...bad coolant temp sensor fuel pump.....lean fuel can cause the other codes you have for misfires