Two days ago my jeep just decided it wanted to get bad gas mileage. Im getting about 150 miles to a tank. No codes thrown, i have no idea whats going on.

 

I'm gonna guess the MAP sensor. My '98 does the same depending on the weather...

 

Mine did the same thing and i had just completed a tuneup. Went back and changed the fuel filt and 02 sensor and mine went back to normal. PO had never changed the ff over 150000. Id also do as BowtieGuy3 says. A friend of mine had to change his MAP to get his mileage back up. Good Luck!!

 

How do you know MAP sensor is bad? How long this sensor will last?

 

one would think if the MAP sensor was bad it would run horrible...what are the condition of the plugs/wires and air filter??

 

I had a 97 rav 4 a few years back and had one of the vacuum lines cracked running to the mass air flow. It would not run for the like of the foreign booger. Maybe it was just that tank of gas you put in. Some gas can give you poor mileage depending on the condition of it.

 

Did you swap a big block into it Seems like it could be a sensor, like an O2 sensor going south or it already left. It can also be a coolant temp switch, if those are bad your computer will be in "limp home-open loop" mode so your fuel mileage would be horrible. Your MAP sends the signal to control the fuel delivery and ignition timing. Heres how you can check to see if its bad. You need a high impedance voltmeter and thats it.

Step 1: with key ON and engine off, the voltmeter reading should be approximately 5 volts even.

Step 2: IF not at 5 then its bad. haha...simple huh, but if not continue.

Step 3: Test MAP sensor terminal 1 and 2

Step 4: Start the Jeep and make sure the voltage is between 0.5-1.8 with engine idling.

Step 5: Then check at WOT or wide open throttle, and make sure the volts are reading between 3.9-4.8

Step 6: If the sensor doesn't on either of these then check the vacuum line for leaks or blockage. If it doesn't have one of these its most likely your sensor.

 

i went to a parts store and they told me my jeeps fuel filter is in the tank

 

yupp thats what ive been told, i know im due for a change but its not going to be easy.

 

I changed my O2 sensor, and my mpg went from 16 to 20. These things wear out. ) 01 model would have an O2 after the cat as well. I'd change them both at the same time if you can afford it. If not, change the one closest to the manifold first.

 

Yeah, that "fuel filter in the tank thing" came with the, I believe the 97+ XJs. The fuel filters in these are said to last until the fuel pump takes a dump. So, you change out both when opening up the gas tank. Trust, me. You won't want to do this just for the fuel filter. It is a royal PITA.

 

Is it a actual filter or a screen?

 

Lay off the skinny pedal

 

X2 on the 02's...OBD II systems will have 2

 

X2 on lay off the D*** skinney pedal!!! Seriously, if you have no fuel leaks, then you have a bad MAP sensor or O2 sensor.