Q: Significant gas mileage drop after tire change

If the vehicle fuel efficiency has dropped 15%, and there is no obvious explanation, something is wrong. The timing of the tire replacement to the drop-off in mileage is undoubtedly just a coincidence unless the tires are wildly defective thus creating, for example, huge rolling resistance. Obviously, make sure the vehicle is properly aligned and tire air pressure is correct. Often, failing oxygen sensors will degrade mileage as will faults with ignition timing. You can use a real time scan tool to confirm operation. Fuel injectors cannot be properly cleaned while installed on a vehicle because each injector has a tiny replaceable internal filter basket. If you ever suspect injectors, they have to be removed from the fuel rail and sent to a lab such as Mr. Injector for cleaning, filter replacement, and testing. There is no other way to do it. The reason shops "try" to clean them on the vehicle is because they can charge you the same amount of money and do almost no useful work. If a filter on an injector is plugged, or the injector spray pattern is way off, or it is leaking, you can clean it all year to no effect.

You can maximize mileage by: keeping the tires adequately inflated; ensuring vehicle wheel alignment is correct; check for stuck brake caliper(s); maintain consistent vehicle speed; make sure engine temperature is in normal range and not too low due to a stuck open cooling system thermostat; check oxygen sensors as worn out oxygen sensors will cause higher fuel consumption; check for worn out spark plugs; low engine compression due to mechanical defects; slipping components in the transmission; dirty or leaking fuel injectors; defects in EGR system; exhaust restrictions; and excess weight in vehicle. If mileage does not improve after verifying all of the foregoing, or if you simply want all the foregoing inspected, please request a vehicle fuel efficiency diagnostic and the responding certified mechanic will get this issue investigated and resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you