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Fuel /computer problems

I recently bought a used 06 tucson it has a digital display for odometer fuel economy and miles till next fill, when i first purchased it it was reading that i was getting about 25.6 mpg 2 weeks after purchasing it the fuel pump went out got that replaced and noticed that now it onlys says about 21.3 mpg. few weeks after the new fuel pump car stalls again thining it was the fuel pump again took it back to the same garage as before to find out the problem is I was out of fuel (gauge reads over a 1/4 of a tank, obviously the float is messed up, they put 2 gallons in started right up so i drove across the street to gas station and filled the tank (it took 16 gallons to fill on 17.5 gal tank) Now hears the strange part the amount till next fill is around 365 mi no sooner did i pull away from the tank and it dropped to about 350 after rougly 6 miles on my trip od. my fuel display dropped to about 340 so i lost 20 mi. worth of fuel in a 6 mi drive. is this a major computer malfunction thats worth fixing and as far as why it never reads over 21 mpg could that be the difference in fuel pumps or what

These mileage range numbers are loose estimates, that adjust based on driving patterns and estimated mileage. It’s plausible the replacement pump doesn’t send the proper information, if it’s an aftermarket pump.

All of those figures depend on the fuel level sender (part of the fuel pump assembly) being correct. You already know that the sender is messed up now. You should realize that is also messing up the estimated range readings. Get the sender fixed correctly, and everything will go back to working correctly.

Don’t try to figure out anything about your gas mileage from those computers. They are unreliable. Fill your tank. Reset your trip odometer. Keep track of your future gas fill ups for the next 500-1000 miles. At that point, fill up again, add up all of the gas (excluding that first tank), and divide the number of miles driven by the number of gallons. That’s the only way to know anything about your actual fuel economy.

Thanks for your response, i know the numbers arent always accurate im just concerned that even the trip odometer isnt accurate right now soon as it gets under half tank i fill it up which according to the trip od im going about 200+ miles

The odometers are usually very accurate - they’re tied to laws. And they’re easy to check anytime you drive down an interstate since most of them have mileage markers.

Information overload. For me I need you to trim it down a bit and ask just a “root” type question, then after I answer you can say, “well when I do xyz this happens,now do you explain that”. Perhaps this “root type question” is “what can I conclude from a previously correctly operating mpg indicator that has now started displaying odd numbers”

Initally I say figure your mileage the old fashion division way or are you concerned that there is some type of cascading electrical system failure that is starting with your mpg indicator? I can’t tell if this is your concern.