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Awful fuel MPG

We had another coil go bad number 1 this time. We made command decision got all coils changed, now Fuel milegage has dropped around 10 MPG. The Nissan runs great better but this fuel mileage is for the birds. My brothers Chevy 3500 Diesel Dulles gets better fuel mileage than me now!!! Dose anyone have any ideas or advice?

nissan quest
Any particular model-year or engine designation or aren’t you that fussy about the quality of the answers? :smile:
Please, Model-Year? Engine? (If you wish)

The first thing I’d do is to make sure the thermostat is working properly.

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Have you asked the place that did the work if they possibly may have disconnected something or if they have a clue?

It is a 2004 3.5 liter.

What fuel economy were you getting earlier?

I would take a look at the air fuel sensor Bank 1. A bad one would not necessarily give you an error code.

First, run it a couple more tanks to see if the mpg’s go back up to what you are normally expecting. Second, check for any diagnostic codes stored in ECM memory, active or pending. Third, check the coolant temp gauge on the dash that it is getting up to the proper operating temperature after 5 minutes of starting. Finally, do a visual check to make sure all the sensors were re-connected properly after the coil work, especially the engine coolant temp sensor. If you’re still having problems after doing that, post back.