Poor gas mileage

[Cjack56]

1990 Ranger XLT 4x4. 4 liter V6, automatic. Getting only 8.5mpg. Been to 2 shops and still don't know what's wrong. Any ideas?

 

[RonD]

Welcome to TRS

Most people use their Odometer to calculate MPG
Ranger 4x4s often get larger diameter tires
Larger tires reduce the odometer miles, so if odometer says you traveled 200miles, you may actually have traveled 220miles
You can get a "speed APP" on your phone, then see if your speedometer is accurate, or if it reads low, if it shows 60mph but APP shows 65mph then odometer is also off
1990 4x4 uses a speedometer gear on the transfer case, easy to change to calibrate speedo/odo to show correct speed and miles traveled

Assuming no gas thieves, lol, and no leaks
Check the Fuel Pressure Regulator's(FPR) vacuum line
In a 4.0l the FPR is behind and below alternator on lower intake, it has the fuel Return hose and a vacuum line, check that vacuum line for gasoline, if found replace FPR

Pull out a few spark plugs, look at the tips, light brown is expected, darker color means computer is running the engine Richer than it should

O2 sensors use a chemical to detect Oxygen in the exhaust, and they run out of this chemical, as they run out they show LEAN, a false lean, so computer runs engine richer than it should, and MPG goes down
O2s should be changed every 100k miles or 12 years which ever comes first to maintain best MPG
O2s are basically free because of the money you save in gasoline over the next 100k miles or 12 years

You don't mention any running issues, are there any?

1990 4.0l 4x4 should be 15-17MPG highway when in tip top shape, lifted and larger tires lowers that a bit, because of the weight of the tires and air flow under vehicle, but not by that much

 

[Dirtman]

A. Someone is stealing your gas
B. Your math is off
D. Your speedo is off which makes your math off
C. Your truck must be running like crap

If it were truly getting 8.5mpg it wouldn't run right.

 

[55trucker]

You're too hard on the throttle?
what are your driving habits?

 

[Dirtman]

You're too hard on the throttle?
what are your driving habits?

Even if he was driving the Daytona 500 with one foot on the gas one on the brake it wouldn't be 8.5mpg. It's simply impossible to be that low without a mathematical error or major engine fault.

 

[fastpakr]

Even if he was driving the Daytona 500 with one foot on the gas one on the brake it wouldn't be 8.5mpg. It's simply impossible to be that low without a mathematical error or major engine fault.

I mean... I legitimately wouldn't question it if he were racing it. It's astounding how much fuel you can burn at sustained WOT. But it would be impossible to duplicate that in ordinary driving.

 

[Dirtman]

I mean... I legitimately wouldn't question it if he were racing it. It's astounding how much fuel you can burn at sustained WOT. But it would be impossible to duplicate that in ordinary driving.

I'm sorry I do not understand.

 

[racsan]

my 93 4x4 with 4.0 & 3.73’s averaged 17/18, best ever was 19 on a trip (would of been better but was in w.va with hills and 70mph speed limits) towing my box trailer milage would drop to 12/14. ran 235/75/15’s.

 

[Broosedamoose]

A plugged up cat will drop the MPG.

 

[Dirtman]

A plugged up cat will drop the MPG.

As will a plugged up colon.

 

[Jazzer]

You can rod both out to clear restrictions......

-Jazzer

 

[Dirtman]

You can rod both out to clear restrictions......

-Jazzer

I'm not up on the current teen webchat lingo.... rod out?

 

[Jazzer]

Some guys with clogged cats remove them and shove rebar through them to gut out the innerds, hence the term “rodding out”.

Thank you for your patience.

-Jazzer

 

[gaz]

Cjack,

How long have you had this low fuel economy issue?