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Poor MPG in a 2005 Ford Sport trac

I have a 2005 Ford Sport Trac that was getting 15 MPG on the highway so I decided to give it a new set of plugs to see if it would help. Wrong now I get 13MPG on the highway and by all topics I have looked at I should be getting 20-21 MPG highway. It is a V6 with 141,000 miles on it…is there any help for me and what should I look at next to improve MPG.

Did you use the Ford OEM plugs? Or did you use some other brand? Were they gapped properly when you installed them? Is the CEL on? Is your air filter clean. I would run a couple tanks with a bottle of Techron in each. How does it idle? Have you noticed a lack of power? Are your tires inflated to the recommended pressures on the door jam? Any or all can affect your mileage.

I agree. I still have my 2000 Ford Explorer, 4.0L V6, and only use Motorcraft platinum spark plugs. You can find them everywhere now, including Autozone.

A bad coolant temperature sensor also will cause poor gas mileage because the computer thinks the engine hasn’t warmed up and makes the engine run fuel-rich.

Repair faults that turn on the check engine light. Use scan tool to see if fuel trim numbers are normal at idle and while driving. Report results. Replace air filter and clean mass air flow sensor. Make sure thermostat is good. Remove weight from the car. Avoid Idling. Inflate tires to maximum pressure. Check alignment and check for dragging brakes.

These vehicles generally get 17mpg in mixed driving.

You should be getting 18-19 MPG highway and about 15 MPG overall.

13 MPG is low. I agree with the others, using the proper spark plugs is important. Is your check engine light on?

All you did is put in new plugs? Assuming they are the identical plug part number as used to be in there, and are one recommended by the manufacturer for this vehicle … hmm … I’m wondering if you’ve accidentally damaged a spark plug or wire in the process and created an intermittent misfire. You may need to remove all the plugs and inspect them, look for any small cracks in the ceramic, and measure the resistance from the top of the plug to the center electrode. And the resistance from the center electrode to the threads, which should be a no connection.

Likewise with the plug wires, carefully inspect them one by one for cracking in the insulation, breakage problems at either end of the connectors, look for carbon tracks indicating a spark is jumping where it shouldn’t, measure the resistance from one end of each plug to the other, etc. Sometimes mechanics will totally darken the room and see if they see any sparks jumping around from one wire to another when the engine is idling.