97zjnoob

I have a 97 zj with the 5.2. Ive had around 6 months and love it. When i got it it had about 210k miles on it and no issues that i knew of. I consistently got 20 mpg. I changed the plugs, wires, cap and rotor, oil and transfer case fluid with in the first month i had it and my mpgs went down. I figured it was from my driving habits. I recently changed from 16" to 15" wheels and went from 225 65 16 to 235 75 15 and noticed a large decrease in mpgs. From 18 to 16.5 mpgs. I changed my diff fluid to 75-90w synthetic and lost another mpg. Why would these changes cause such a dramatic decrease in mpgs?

Also my fuel guage will randomly read empty after i start the truck. Thanks in advance for any advice or helpful tips!

go-part

Well the gauge sounds like the sender unit may be malfunctioning.
http://oskin.ru/pub/chrysler-dodge/m...kee/EZG_14.PDF

Sensor issues can cause a dramatic drop in fuel economy.

97zjnoob

Ive not replaced any sensors yet i.e. o2 and what not. There is a very minor exhaust leak. I was gonna do it all at once since its all stock and original. And thanks for the Download! Looks like good info. I was just concerned that it just seemdd to be such a rapid decrease but i guess it could be because i do drive alot.

kennzz05

dont forget winter blend fuel also decreases mileage
you arent getting an accurate speedo reading due to tire size hence the apparant mileage drop http://www.1010tires.com/tiresizecal...?action=submit

only way youre gonna get an accurate reading now is useing a gps to track mileage than divide that by fuel used

interesting note i just figured out that my xj was getting way better mileage than i thought it was as mine was off by almost 13% i never got more than 17.5 on the road now i know it was probably 20 at least

dave1123

What would have we done if the DOD hadn't put those satelites up there?

97zjnoob

I wonder if the gps on my phone tracks speed? Ill have to figure out the percentage off it is. I know its throwing off my oil change tracker too since it goes by miles.

97zjnoob

The tire link says there is a 4.9% change in my speed. So my speedo says im doing 60 im actually doing 57.1 mph. How do i calculate that into the difference in mpgs? Or is the gps the only/best way?

kennzz05

round it to 5 % 17x.5= .85 so almost 18 remember all this is only gonna be accurare is the tires you took off were stock size

also look for a speedometer app on your phone

97zjnoob

Brilliant! I love talking to people smarter than me haha