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sudden drop off in fuel efficiency


Sturg1647545502

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For the past 2 fillups ive had a 33% drop off in fuel efficiency. Taken care of the obvious stuff oil change, air filter, tire pressure check, fluid check...all with no change. no engine light, change in driving style or odd sounds/feels. Im not down on power either. Maybe clogged fuel filter?

 

This is on my DD a 2002 mazda tribute with 195k

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Weather, plugs, o2, clogged cat(s). If you don't have a scanner, get it scanned. Just cuz the engine light is off doesn't mean it hasn't thrown a code.

 

Those are quickly off the top of my head.

 

Quick update:

Also, be sure you don't have a brake or parking brake dragging. With all the cold, moisture and salt with an older car it can become a real possibility.

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cold weather, I get 22mpg in this cold versus 26 in warmer weather.

the week it warmed up i was back to 25mpg

 

maybe, but in 5 years with this car its the 1st time ive noticed it

 

Weather, plugs, o2, clogged cat(s). If you don't have a scanner, get it scanned. Just cuz the engine light is off doesn't mean it hasn't thrown a code.

 

Those are quickly off the top of my head.

 

Quick update:

Also, be sure you don't have a brake or parking brake dragging. With all the cold, moisture and salt with an older car it can become a real possibility.

 

thanks, I wouldn't have thought of that

 

Did you switch brands of fuel?

 

My car gets 29 with Certified fuel, but 35-39 with Sunoco.

no, pretty consistent here.

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Any number of things can effect fuel economy, basically anything causing drag or rolling resistance is what should be looked at along with making sure the engine is operating effeciently. Proper brake function with no drag, proper trans function with no slip, properly inflated tires, tires that aren't excessivly worn or soft, excess weight in the vehicle. When someone scans the vehicle for codes they should also be looking at fuel trims to help judge proper operation, and if they don't know why you should find someone who understands what they are looking at. Looking at o2 sensor operation to see that they are coming to life quickly after start up and switch fairly quickly. Obviously the last few require a decent scan tool, and a tech with a little knowledge.
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