I have a 2002 xlt 4x4 auto with about 200,000 km on it and recently the truck started feeling a bit under powered than normal and it's gotten to the point that I struggle to get the truck to highway speeds and even maintaining 100kph feels like a challenge. I have noticed the occasional misfire at higher rpm when going up a hill or with some weight in the bed. I'm planning on throwing plugs wires and a coil on it. The previous owner changed the plugs at 160 but I don't believe they were the right ones. However I'm doubtful this will fix my issue so any feedback would be appreciated.

 

I would replace the fuel filter if it hasn't been done in the last couple years. The 200,000 km miles may not be enough to have bad catalytic converters, but the age may be enough. I had one of the front cats break up and clog the main cats at around 250,000 miles. The other front cat was getting bad too. Could be something to check out. I replaced all the cats.

 

Yes, on the spark plugs, 4.0l OHV or SOHC wears out spark plugs pretty fast, regular copper or double platinum only, single platinum will wear out same as regular copper so waste of money

If you have or can get a Vacuum gauge($30) you can test for partially blocked exhaust
Also check air cleaner

Engine is a self powered air pump
If air can't get IN easily and OUT easily it won't work very well, lol



And just FYI, and NOT your problem
The 4.0l SOHC engines(2001-2011 Rangers) run 9.7:1 compression ratio, which means they can not run 87 octane fuel(regular) as is
They have a Knock sensor to detect pinging/knocking when regular gas is being used, this changes spark timing which reduces power a bit
Running 89/91 octane will increase power and MPG just a bit but usually not worth the extra expense
If you will be pulling a trailer or otherwise hauling a load putting in some higher octane fuel is not a bad idea but just for that trip

 

When OdoMeter hits 200kMiles,
personal preferences for this 2001 V6~4.0L~SOHC Engin + 5r55e Trans + 1354 TCase + 4.10 Diffs,
it's time to:
* renew 2 OilPressurized TimingTensioners. 1stChoice=MotorCraft 2ndChoice=Cloyes\Melling, every 100kMiles\12yrs
* renew 6 SparkPlugs+Wires, AutoLit\MotorCraft, every 100kMiles\12yrs
* renew 3 OxSensors, Bosch\MotorCraft, every 100kMiles\12Yrs
* renew FuelFilter, every 100kMiles\12Yrs
* renew BrakePads, Ceramic, every 50kMiles\6Yrs
* renew+flush Engin Coolant+RadCap+ThermoStat, Yellow\Gold Peak#10X\Zerex#G05, every 33kMiles\4Yrs
* renew Trans MerconV.FullSyn+Filter, every 33kMiles\4Yrs
* renew TCase MerconLV.FullSyn, every 33kMiles\4yrs
* renew Diffs GearOil.FullSyn+HiTemp, 75w140@Rear 75w90@Front, every 33kMiles\4Yrs
* clean MAFSensor +Throttle +EGRValve +IACValve +IntakeManifold, every 33kMiles\4Yrs
* renew Engin Oil+Filter, every 5kMiles\6Mths: 5w30.FullSyn for TypicalConditions, 0w20.FullSyn for ColdClimate, 5w40.FullSyn for HotClimate
* renew 1/4qt MerconV.FullSyn @SteeringReservoir with HandPump, every 5kMiles\6Mths
* renew 3/4qt MerconV.FullSyn @TransDipTube with HandPump, every 5kMiles\6Mths
* renew\clean AirFilter, every 5kMiles\6Mths
* inspect Hoses+Radiator+Battery+Belt+Fan+FanClutch every 5kMiles\6Mths
* clean Injectors with a bottle of FuelSystemCleaner +PremiumFillUp, every 5kMiles\6Mths

 

well it has been a wild week but I finally managed to wrench on the truck. I replaced all I mentioned as well as a fuel filter and all my problems were solved, the truck drives great. I suspect the NGK spark plugs are probably the cause, fords don't tend to like them.