Bad mpg help!
 

i have a 2001 ford ranger 4.0 supercab edge with 16inch Patagonia A/T tires and 157,000miles. i recently changed the oil, oil filter, spark plugs and wires, cleaned EKG valve and MAF sensor. I get a whopping 11.9mpg city and 15/16 highway. Nothing has ever gone bad with this truck. i bought it from my uncle about 8 months ago i have been getting very bad gas mileage. i do notice around 2500/3000 rpms when im going up hill i hear a rock rattling in a can type of sound, i believe it might be the timing chains but that started doing that a month ago. And i dont think that would effect my gas mileage alot.
Anyone know what could be the problemhttps://www.ranger-forums.com/rf/images/icons/icon5.gif

Welcome to the forum

How do you determine MPG?

If you don't have Stock tire size then Odometer will be off
On the drivers door, back edge, will be a label with stock tire size, thats the size the speedometer/odometer is calibrated to

If your current tires are "taller", larger diameter, then odometer will read low, so if it says you have gone 100miles you probably went 105-110miles with the larger diameter tires.

If MPG has dropped recently with no other changes then it could be system related.

Obviously a fuel leak, even a small one will cause lower MPG.
Not all 2001 Rangers had a Fuel pressure test port, it would be located on the Fuel Rail, what the fuel injectors hook to, it looks like a tires air valve, because it is, it is a schrader valve, and works the same way, you can test fuel pressure using a gauge that goes up to at least 100psi.
2001 Ranger should run at 60psi fuel pressure
When you shut of the engine/key the fuel pressure should hold above 45psi for a few MONTHS, so no leaks if it holds.

The gas tank Filler tube on the side of the bed and Vent hose can leak, so when tank is above 1/2 fuel can slosh out and evaporate while going around corners

Park on level ground, engine off key on, put trans in neutral and push the truck forward and backwards to see if anything is "dragging".

Run higher tire pressure, tire pressure specs are not to be taken literally, you run the best pressure for YOUR USE, they are YOUR TIRES.

Check computer codes, WRITE THEM DOWN!!!!
Any auto parts store will check codes for free

You have two upstream O2 sensors, O2 sensors use a chemical reaction to detect oxygen in the exhaust, O2 sensors do wear out, chemicals get used up.
Manufacturer's recommend changing O2s every 100k miles, I say 150k, lol
But in any case O2s fail "lean", as the chemicals run out they tell computer exhaust is Lean so computer adds more gasoline than needed, so MPG goes down.

Rear O2, downstream, lasts 3 times as long as upstream.



Yes that noise is most likely timing chain, and yes it would not effect MPG, but...................
The 4.0l SOHC engine runs 9.7:1 compression ratio so it will be "pingy" on Regular gas, Ford added a Knock Sensor so it could run Regular 87 octane fuel
Knock sensors detect "noise" in the engine, when activated the computer advances spark timing to prevent pinging/knocking.
This spark timing change reduces power and MPG but it would only be temporary until "noise" was gone.
And there in lies the problem with an engine rattle and MPG when a Knock sensor is involved.

Knock sensor doesn't hear "noise" like we do, it hears engine vibrations, a sharp "noise", that we can't hear

A Live Data OBD2 reader should be able to view Knock Sensor data to see if it is being activated by timing chain rattle