Another 4.0 with bad MPG

[iceman.kcmo]

Hi all. First post. I mostly just read and search. I have been searching for about a month trying to figure out this MPG problem. Previous owner said he was getting a consistent 20 mpg out of current sent on old engine. Original engine blew a head gasket and i found an engine from a 92 with 84k miles for $350. Cheaper than i can do a head gasket right.

Engine runs good. It does have a slight miss at idle and maintaining highway speeds takes a little more pedal than i think it should. Currently getting 14mpg. Here is all the information.

93 Ranger 2wd Auto Stock 3.08 gears.
4" suspension lift
33x12.50 15" tires


Engine from 92 with all the 93 components swapped.
Kept EGR, working properly
Swapped ALL sensors. (tried both sets)
New maf
CAS is timed correct (CA truck)
New spark plugs Autolite iridium (getting ready to swap to copper plugs instead)
New Wires
Swapped coil packs
Injectors are from the 92 engine (going to swap those this weekend)
New Radiator and heater core (just thought i would let you know)
Converter has been hollowed out (thought it was a plugged cat)
New O2 Sensors
New FPR
EGR valve works like it should.

*Updated*

New Thermostat


Now I cant believe the tires and lift are draging me down so much. I have seen a few guys here getting at least 18mpg. I would be happy with just 16.

As I answer questions, I will try to update to first post with that info. As i think of more things I will update.

Thanks.

 

[adsm08]

The problem is that you replaced a good engine with an unknown one. Saying that it takes more throttle to hold highway speeds makes me think the new to you unit is worn more than the original one. More pedal means more fuel.

Frankly, 3.08 gears aren't fuel-friendly either, even with the stock tire size.

 

[BRUTUS_T_HOG]

Tall rear gears. Tire size. 4.0L. Winter fuel. Winter weather.

14MPG sounds pretty damn good.

Just make sure the thermostat is good and that you're reaching operating temperature and that's about all you can do.

 

[iceman.kcmo]

It is a new Thermostat, but not a motorcraft. I do have a motorcraft thermostat sitting around.

Right now it does not get past the N on the NORMAL of the temp gauge. I really hope i can get more than 14mpg.. If not, looks like i am finding something else.
If i am going to get 14mpg, I better have alot more power.

 

[BRUTUS_T_HOG]

Well you have highway gears and big tires. You won't have much power or fuel economy.

 

[ronclark]

Hi all. First post. I mostly just read and search. I have been searching for about a month trying to figure out this MPG problem. Previous owner said he was getting a consistent 20 mpg out of current sent on old engine. Original engine blew a head gasket and i found an engine from a 92 with 84k miles for $350. Cheaper than i can do a head gasket right.

Engine runs good. It does have a slight miss at idle and maintaining highway speeds takes a little more pedal than i think it should. Currently getting 14mpg. Here is all the information.

93 Ranger 2wd Auto Stock 3.08 gears.
4" suspension lift
33x12.50 15" tires


Engine from 92 with all the 93 components swapped.
Kept EGR, working properly
Swapped ALL sensors. (tried both sets)
New maf
CAS is timed correct (CA truck)
New spark plugs Autolite iridium (getting ready to swap to copper plugs instead)
New Wires
Swapped coil packs
Injectors are from the 92 engine (going to swap those this weekend)
New Radiator and heater core (just thought i would let you know)
Converter has been hollowed out (thought it was a plugged cat)
New O2 Sensors
New FPR
EGR valve works like it should.

*Updated*

New Thermostat


Now I cant believe the tires and lift are draging me down so much. I have seen a few guys here getting at least 18mpg. I would be happy with just 16.

As I answer questions, I will try to update to first post with that info. As i think of more things I will update.

Thanks.

Don't use autolite plugs in a ford your just asking for trouble down the road, go motorcraft and never look back.
I am not sure were the year breaks are but there is a chance the injectors are different.
I think adsm08 is right you may have a worn engine, i would do a compression test that will give you a good idea how badly worn it is.

 

[Edgefevah]

tried hooking up the O2 sensors the opposite way. I hooked up my O2 sensors wrong once and had a miss and POOR gas mileage. turned out I had just plugged the O2 sensors backwards.

 

[Dune Runner]

Those tires and gears have got to be killing you. A set of 4.10s would wake that thing up and help your mpgs at the same time. Were those tires on the truck when you bought it?

 

[martin]

33" tyres with 3:08 gears is not helping but are you calculating the tyre size difference into your calculations, ie your odometer reading will be quite a bit off with the larger tyres.

 

[iceman.kcmo]

tried hooking up the O2 sensors the opposite way. I hooked up my O2 sensors wrong once and had a miss and POOR gas mileage. turned out I had just plugged the O2 sensors backwards.

Yup. Did that already. I was getting Lean and Rich codes, and 8 mpg.

Those tires and gears have got to be killing you. A set of 4.10s would wake that thing up and help your mpgs at the same time. Were those tires on the truck when you bought it?

I found a set of 3.54 gears localy for cheap. Thought about tossing those it, but i am holding out for a locking diff of some sort. The tires were on it when i bought the truck.

33" tyres with 3:08 gears is not helping but are you calculating the tyre size difference into your calculations, ie your odometer reading will be quite a bit off with the larger tyres.

Yes, I did compensate for the tire size.

 

[Showboat911]

tires are a new variable int eh equation?

are the tires different than you had before? then the tires are not what made the difference. its more than likely the injectors, map sensor, and other data transmitting components are not what the ECM is looking for, or use to. if the engine you currently have came out of a different type vehicle, then your ECM is not running it at its optimum capabilities. I took basically a long block 351W out of a 90' conversion van and put it in a 90' F-150 4x4 using all the 351W parts from the pickup and used a 90' Crown Vic ECM, and could white smoke all 4 tires on dry pavement and could outrun most mustangs and camaros, a 4.0 isnt the same 4.0 just because the displacement is the same. all different vehicles have different peak performance settings due to all the variables. I'd check into getting your computer re-flashed if you feel confident the engine is in sound operating condition. check to see exactly what vehicle the engine came from, check injector sizes, fuel pressure, throttle body size... ect.