poor fuel economy

[2'91fords]

my 91 auto with 160,000 mi, 3.73 gears and 30's has been progressively losing power and fuel economy. i got 17 mpg highway when i first bought it with 150,000 on the clock, and it pulled ok going uphill. now i'm struggling to keep it at 75mph going up short, unsteep hills and i'm averaging about 11-12 mpg highway. i have done plugs, wires, fuel filter, catback w/flowmaster, conical air filter. i have also taken the maf off and cleaned it and the throttle body. i have added a cargo box and light bar on the roof, but i can't imagine this causing a 5-6 mpg drop. any suggestions?

 

[aldive]

Have you checked the function of the O2 sensor(s)?

 

[metstalker]

any pinging?

 

[2'91fords]

no pinging. how do i check the o2 sensors? im not throwing any code

 

[Creager]

are you running cold? make sure your thermostat is not stuck open.

 

[2'91fords]

new motorcraft thermostat, heats up and sticks right around the N on stock gague

 

[jfman]

running colder makes you use more gas ?

my explorer runs on the cold side. Barely get up to the bottom of the guage.


I get 18.2 mpg on the interstate at 70 and 17.3 mpg at 75-80.

 

[Creager]

Yes running cold will force the engine to run rich to make up for the tempature, hense a decrease in gas mileage.

When my gauge was reading N, i considered it running cold.

when it would hover around N, i would get ~15 miles per gallon

when it would go between the O and the R i would get ~18

But every truck is different.

 

[jfman]

I will put a new T-stat in mine. my needle barely budges.

 

[Creager]

your gauge might be a fault more then the thermo, since you are seeing normal gas mileage i wouldnt start with the thermo.

 

[aldive]

Don't base much on the dash "gauge", actually test the temperature.

 

[jfman]

since you are seeing normal gas mileage i wouldnt start with the thermo.

18mpg on a stock explorer is very poor IMO

My 2002 lightning was getting 16.5 and it had a supercharged V8 under the houd AND an auto tranny.

 

[Creager]

haha, really? im sure 90% of the people on this forum would love to see 18 miles per gallon out of their 4.0 OHV =)

highest ive ever calculated was 19 miles per gallon.

 

[SuperEx91]

so what can i expect with 9 inches of lift and 35s then?

the best way to check the o2 senseors is to hook it up to a scanner and watch the readings. obd1 vehicles should only have pre cat sensors and they should flucuate between 100 mv and 900 mv after the vehicle is at normal operating temp. but if they are bad, i would think it would throw a light(unless the light is out, the scanner can tell you if there is power to the light or not)

if the o2 sensors are good.......maybe leaky injectors. i dont know. i havent had my explorer long enough to drain a tank yet.

 

[jfman]

haha, really? im sure 90% of the people on this forum would love to see 18 miles per gallon out of their 4.0 OHV =)

highest ive ever calculated was 19 miles per gallon.

How can it be so poor on a mid sized SUV !

My mom was getting 19-20 mpg in he full sized chevy tahoe withj a 5.3 v8 ! I was hoping for a little better than 17-18mpg...





Nice sig super X Convert to manual tranny and be done

 

[Creager]

you honestly will rarely see 20. To be honest, be happy if you get 16-17 with an OHV.

 

[tweakedlogic]

The reason for the better economy on the newer truck is the motors and the computers that control them are much better.I toyed with the idea of buying a rolled 03 and going throught the hassle of swapping everything. but I decided it wasn't worth it.

 

['97 V8]

take the cargo box off the roof..tey reduce milage and see if that brings it back up...but you stated you struggle on hills so i dont know about that. What rpm are you at at 75mph?