Poor Gas Milage <170 Miles out of a $50tank

[burnstony]

I just purchased this explorer a couple months ago from my brother and had to replace the timing chains to get it on the road. Lil did I know I was going to use 200+ a week in gas!

The only modifications done to the vehicle is upgrade the tires from the factory to Firestone Destination M/T - P265 70r 16s. I did adjust the torsion bar in order to allow my tires to fit and my front end does sit a lil higher than stock. But even before the upgrade my milage was about the same. I am at a loss of words and don't have any idea how to fix it.

I ran an OBDII Test on it and it's response is as follows...

OBDII SCAN
(IF scan needs to be run with vehicle on for better result please let me know)

​

Trouble Codes:
Error Code PO420 - Catalyst System Efficiency Below Threshold

I/M Status
Missfire OKq
Fuel System OK
Comp Com OK
Catalyst OK
Heated Cat N/A
Evap System OK
2nd Air Sys N/A
A/C N/A
02 Sensor OK
02S Heater OK
EGR System OK

Freeze Frame Data:
Fuel System 1: Closed Loop
Fuel System 2: N/A
Load Value: 49.9%
Coolant Temp: 188 Degrees F
STFT-Bank 1: -1.5%
STFT-Bank 2: -3.1%
Engine RPM: 1795 RPM
Vehicle Speed: 20 MPH

Live Data:
Coolant temp 188 Degrees F
STFT-Bank 1: -99.8%
LTFT-Bank 1: -99.8%
STFT-Bank 2: -99.8%
LTFT-Bank 1: -99.8%
Engine RPM: 0RPM
Vehicle Speed: 0MPH
Ingnition advance: 0.0 deg
Intake Air Temp: 78 deg F.
MAF Air flow rate: 0.0 lb/min
Throttle Possition: 18.7%
Bank 1- Sensor 1: 02S Output 0.000V
Bank 1- Sensor 1: STFT - 99.8%
Bank 1- Sensor 2: 02S Output 0.000V
Bank 1- Sensor 2: STFT - 99.8%
Bank 2- Sensor 1: 02S Output 0.000V
Bank 2- Sensor 1: STFT - 99.8%
Bank 2- Sensor 2: 02S Output 0.000V
Bank 2- Sensor 2: STFT - 99.8%

Vehicle Info:

• OBD2 Protocal: SEA PWM

OBD2 Protocal: SEA PWM


This is the information I have obtained. Please if anyone can help let me know. I get between 8.5MPG - 10MPG.....And thats just insane!

Anyone with advice please post back. I am about to sell the truck do to the

 

[team]

what was the stock tire size?

 

[burnstony]

My explorer came stock with p255 70R 16. So I don't beleive this is enough difference to affect my gas "That" much is it?

 

[chezoom]

i have 255 70 16's also but i get even worse sometimes. with NO WOT...i ussually got 220-240 a tank but now its between 160-190
my truck has 48,000 on it to

 

[XLT]

Something is surely wrong. I have a 98 ex with the sohc and usually average about 16mpg. The bigger tires could effect mpg a little. Since they are bigger you should be getting a little better mpg then what your odometer is reading since the bigger tires through it off.

 

[2000StreetRod]

Scanner assistance

Your scanner can provide valuable assistance in diagnosing your poor fuel economy. Set up a configuration file for recording engine coolant temperature, engine rpm, absolute throttle position, MAF sensor airflow, inlet air temperature, spark advance, Bank 1 & 2 STFTs and LTFTs, instant fuel economy and vehicle speed.

Record live data from a cold engine start to see that your engine temperature increases to the thermostat rating. A sticking open thermostat can cause poor fuel economy. Your LTFTs should be "0" for idle during warmup and drive. Your STFTs should be between +10% and -10% and bank1 STFT should be no more than 10% different from bank 2 STFT. The spark advance should be around 15-20 degrees at idle, 20-25 degrees during acceleration and 35-45 degrees at cruise.

If your STFTs and LTFTs are abnormal then record your O2 sensors and watch the voltage swings. Make sure the PCM goes into closed loop within a minute or two after engine start and stays there except during rapid acceleration.

 

[Elessar65]

Winter blend fuel gives poor gas mileage. I usually get from 15-19 during the summer, and 12-15 in winter. From around 300 miles a tank to around 200 or less. Also you vehicle idles longer in the winter time, and takes longer to warm up so that the torqu converter will lock up.

Do a search for the code that its throwing with the cats and see what other people have done/said.

That change in tire size isn't really enough to effect the fuel mileage to the extent you are seeing. When you go to larger tires you should get worse mileage around town, because it takes more power to get it moving with the larger rotational mass of the tires, but better on the highway at speed because they are fewer revolutions per mile. Like I said though thats a pretty small change. 3.8% increase in diameter.

 

[Elessar65]

Hmmm,
This might seem like a lot of work-
but if you were to swap the rear o2 sensors for the fronts, and fronts to rear-
it would eliminate something-

if the code returns you may have clogged catalytic converters
if it changes to a "rich -lean" condition report, it would indicate bad o2 sensors.

It's free, and worth a shot.

You don't happen to have an exhaust leak? Could you check the DPFE hoses real quick?

 

[my98nnj]

Were the cams set up correctly with the alignment tool when the chains were done?

 

[corkey]

i would say tires size is a big reason that your mileage is sucking gas,
you say you wet to a 265/75/16 from the other, well, do you know what rearend gear this thing has, ?

i went from a 235 to a 31 inch tire and my gas mileage went down quite a bit at first as well

 

[Elessar65]

No Pete, he went from a 255/70 to a 265/70. Thats like only half an inch in diameter bigger. 30.05 inches to 30.60 inches. It will effect the mileage, but not that much I wouldn't think.

 

[kert0307]

Keep this in mind.

1. You have a sport, the tank is smaller than a 4 door explorer = more fill ups
2. Winter blended fuel = worse mileage
3. Have you been driving around in 4x4 high? that will make it worse
4. Have you been letting it idle for long periods of time to warm up?


In winter driving around town in 4x4 high, I only get about 12mpg. Summer rolls around and I get 17-19mpg

 

[BBQ Bandit]

Tire tread will play a small factor... rolling friction/resistance .
(aggressive mud verses a highway tire)

 

[corkey]

well, he went to a 265 75 15 tire,, stock on that Explorer was a 235 75 15, not a 255 75 16,so in fact he went from a 28.5 inch tire to a 30,6 inch , , it wasn't till later that they went to a 16 inch rim , i bet if he went to a 235 tire again his mileage would be alot better, he even said he had to do the tt to make it fit,

also fuel mileagae in 4x4 will be worse on top of that ,

 

[jchopo01]

98 Explorer Sports have 16 inch rims. 255/70/16 stock tire. He went to a 265/70/16 which isnt much bigger. I plan to go to a 265/75/16 and expect to have the same mileage or better because of the 4.10 gears.

I seem to magically have this problem, but around 12mpg and my front diff is out of the truck. Mine is associated with a gas leak I believe. Smell any gas? lol
I would say timing probably.

And I do not believe that 4x4 on this truck will change mileage much because of the lack of any axle disconnect.