my dad use to be a mechanic back in the day but yeah rear main seal is a b*tch

 

oh god does fluctuation oil pressure mean i have a cracked head ?

 

I keep track of every tank of gas; my 97 4.0 5-Speed got 22.2 on its last tank, thats with the AC on all the time, city and hwy combined.
My 96 4.0 5-Speed gets right at 20 during the summertime. Both do better in the winter of course. Do you have an automatic?
I run accel plugs and wires. I use Royal Purple 10-30 oil.

 

yeah i got an auto with towing package

 

cant believe know one mentioned this. 02 sensor, especialy the before cat sensor. I have seen on many occasion no codes but horriable milage. I actually remember a dodge caravan with no codes but getting 4 MPG!!! Yes, only 4 MPG. The o2 sensor was reading wrong, reading lean. Which won't always throw a code. Replaced it and problem went away.

 

Also egr valve has to work properly, and do a compression test on your engine too. If your egr don't work bad gas mileage, same with low compression, I just had this issue with my metro so I have first hand experience.
Also my jeep only gets around 12 mpg however it's lifted on 31's, but I still need to do some checking.

 

X2 on the O2 sensor

And drive with that egg shell under your foot on the skinny pedal

 

O2 sensor are reading lean constantly so cpu compensates, you're running rich wasting gas. change both sensors. been there done that. anyway should change every 50000km or 30000miles. good luck

 

No, fluctuating oil pressure is pretty normal. Mine idles at 25psi when warm and about 50psi when driving 55+ mph. I can't believe I forgot about the 02 sensors, do you have a check engine light lit?

 

replace o2

 

I forgot about this, about 4 months ago I had a problem with my upline o2. I changed it out and everything work better. The PCM gets info from the o2 which it uses to control the injectors and air flow.

 

170 is about 13mpg on a 14 gallon tank, like mine. What size is yours

 

get rid of the +4's, I wish people would stop buying those!!
run a compression test, if everything is over 100, then its time to change out those plugs, put a stock air filter in, make sure your breaks arent dragging..

 

i use autolight plugs. not the best in the world but cheap and have never done me wrong! do you have any oil in your radiator or is your oil a milky whitish color? that would be the symptoms of a blown head gasket. no reason to replace it if it is fine. also you can check for vacuum leaks by listening for a sucking sound in your engine bay, your idle will also be slightly higher.

 

Replace plugs with OE Champions... your 2000 might have up to four O2 sensors if you have the cat's in the manifold and the one in the exhaust under the body. The ones' in the manifold on my 00 xj cost me around 70 a piece. But like everyone said..
check air filter.
replace plugs with OE
check compression
replace leaking headgasket.
and drive lightly