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03 explorer 4.6 REAL BAD GAS MILAGE

gforceman

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2003 limited 4.6 V8
im getting 9 mpg around town and its killing my pockets , the only thing i have done it in the past few months was a plug change air filter change , and recently replaced the IAC valve and cleraned the MAF sensor ,im not getting any lights or codes on cluster just real bad milage , the exhaust doesnt smell like gas either any thoughts to why thx
 



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matt0248

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There are many possible causes for poor MPG's so it is really had to say for sure, especially with out a check engine light or an obviously poor/rough running engine. Possible causes could be a bad MAF sensor, leaking fuel pressure regulator, incorrect fuel pressure, vacuum leaks, degraded oxygen sensors, bad gas, a bad thermostat will not allow the engine to get to proper operating temp.

Is the bad mileage just the reading on the message center, or are you actually calculating the MPG's? Have your driving habits changed, i.e. different work schedule or route?

EDIT: add plugged exahust to the list of possible causes.
 












slammed98z

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fedyfedz

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2002 limited v8
clean throttle body, check tire pressure, change air filter, i get 15-16 around town and 21-22 hwy with my 02 v8 limited
 






gforceman

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its telling me that in the message center , just this past couple of weeks before that i was getting 13.9 around town the tires are 35psi NO smell of gas in exhaust, i replaced plugs with autolight double platinums about 2 months ago and recently replaced the idle air control valve , i guess ill be checking things like vac leaks and or lines disconnected , fuel regulator etc ...
 






fedyfedz

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are you actually calculating the mileage or going by the onboard computer. if you are going by the onboard computer its not accurate
 






fusseli

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doesn't sound right. 118k on my 4.6 mounty and i get 12-14 in town and 18-20 highway, according to the message center.
 






yglide123

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I think it depends on the city you're driving in too... I live in San Francisco with lots of hills and probably get 9ish in the city too.... and maybe 17 or 18 on the freeway. My computer shows an average of 14.9 most of the time (unless lots of city driving)...
 






fedyfedz

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also if your computer gets reset or u reset it urself and ur heavy on the pedal the mileage on the dash is going to be relatively lower than if u reset it on the hwy and drove like a granny, it will show u get better mileage then over time it will slowly go down and level off if you driving levels off as well. watch when u hit the reset button while on the mpg screen and watch how sensitive the reading is, if your going down hill with foot off gass it will show a crazy high number until u give it more gas.
 






1AJeremyD

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Might be a silly question to ask but......you forgot to mention the last time the fuel filter was replaced. Might be time to swap a new one in it
 






gforceman

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so far i owned the truck for 8 months and i think it was NEVER changed 113k now ..


update : on the passenger side of motor on the fuel rail theres a valve like thing with a vaccum line on it is that the pressure regulator ?? i was looking at it today and disconnected the vac line off of it to see if there was gas in line , i forgot to reconnect it and drove it and saw my mileage went from 9 mpg to 15.5 to 14.2 mpg i guess to say that part is bad ?? and the pass side fuel rail will have to be replaced , becasue the valve is welded on to rail ..


ill just do this >>>
ITs pretty simple to check the Fuel Pressure Regulator. Its located passenger fuel rail to the front of the rail. It has a vacuum line going to it. Remove the vacuum line to see if there is any raw fuel in it. With the line off you can cycle the key on and off to prime the fuel system and recheck. Plug the vacuum hose with a golf tee and start and run the truck, recheck for any signs of leaking. The last trick I have is to (with the truck off) Cut a very thin strip of paper, small enough to go into the vacuum port in the regulator. Stick the strip into the vacuum port and wait 10 minutes. Remove it and see if it appears damp and smells like fuel.
 






gforceman

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whewn i disconnect the vac line off the pressure regulator and drive it i get better mpg on the info center 14.5 with vac line off ill get 10 . maybe the regulator is bad ?? i also NEED to replace the fuel filter it may be old but how can that affect mileage

when u hit the reset button while on the mpg screen and watch how sensitive the reading is, if your going down hill with foot off gass it will show a crazy high number until u give it more gas.

when i reset my MPG computer when i left off the gas it will NOT show a crazy number for gas milage it will go up some but not crazy like 55mpg then drop when i hit gas ,
 






fusseli

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whewn i disconnect the vac line off the pressure regulator and drive it i get better mpg on the info center 14.5 with vac line off ill get 10 . maybe the regulator is bad ?? i also NEED to replace the fuel filter it may be old but how can that affect mileage



when i reset my MPG computer when i left off the gas it will NOT show a crazy number for gas milage it will go up some but not crazy like 55mpg then drop when i hit gas ,

The more clogged a filter gets the bigger the pressure drop acrossed it. My guess is too low of fuel pressure results in a less efficient burn in the cylinders-- just a guess though as to why. Fuel filter is a 10min/$10 fix, on almost any vehicle.

and yes if a fuel filter is clogged bad it will provide lower MPG, that much I'm sure of.
 






gforceman

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i totaly agree with you its problery the original filter and with 120k on it its time for change .. but ....

when i disconnect the vac line off the pressure regulator and drive it i get better mpg on the info center 14.5 with vac line off ill get 10 . maybe the regulator is bad ??

what do you think of that ?? thx
 






matt0248

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When you remove teh vacuum line from the regulator the fuel pressure increases about 8-10 psi. So, rent a fuel pressure gauge set and check fuel pressure, check with the engine running with the vacuum hose connected and disconnected. record the gauge readings. Turn the truck off and it should hold pressure, if it is losing pressure you could have a bad pressure regulator, leaking injector, or bad check valve in the fuel pump assembly.
 






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