I have a 2002 Chrysler Town & Country FWD with 3.8L V6. Recently, I had an error code of MISFIRE CYL 5. I changed my spark plugs and added some injector cleaner to fuel tank with no results. Then I replaced my ignition coil and the misfire stopped (according to engine computer after reset and smoother engine). While it was misfiring, the gas mileage was reading about 10-11 mpg city. I changed my oil and air filter, switching to all 10w-30 synthetic oil. Since then, my mpg reads around 8 mpg! Before the misfire, I would get 17 mpg in the city. One other issue that coincides is a 10-12" long thin vacuum hose near the engine snapped and I replaced it with a common rubber hose. The hose I replaced it with was at least twice inside diameter. I think I need to get the reducer/thin hose setup from a dealer. Any idea if the vac hose would be reducing my fuel economy by 7 mpg? Or did i screw something else up when changing the oil and coil? The engine seems to be running smoothly and I’m having no noticeable problems aside from paying $4.39 for a gallon of gas that takes me 8 miles!!
Since then, my mpg reads around 8 mpg!
How are you calculating your mileage??
The CORRECT way is to fill the gas tank…then divide the number of gallons during the fillup into the number of miles since your last fillup. That will give you the gas mileage during that tank full. Repeat this several times for a more realistic average of your gas mileage.
I’m just relying on the digital readout of avg MPG
I'm just relying on the digital readout of avg MP
Don’t. They can be notoriously inaccurate. Only determine your gas mileage by the method I described above.
"The hose I replaced it with was at least twice inside diameter."
Sounds like you may have a self induced vacuum leak, depending on how the hose attaches.
I dunno if you had a misfire you may have wrecked the cat converter or the o2 sensor or you haven’t corrected the original problem. If your mileage is in fact that bad, you may just need to spring for a $100 computer diagnosis to check for sure.