I have a 1994 grand Cherokee laredo 4.0L inline 6. I used to get around 16 mpg. Over time it has slowly decreased and now I'm only getting 8-10. Any suggestions on how to improve my mpg
-thanks
Ryan

 

When was the last oil change?

Tune up? (Plugs, wires, cap, rotor, air filter)

O2 sensor replaced?

 

I changed the oil and filter less than 1,000 miles ago I have recently replaced the spark plugs, caps and wires about a year ago air filter is clean (would you recommend a k&n). I'm headed to the parts store now to get a new o2 sensor is there any thing else I should pick up that would help?

 

Seafoam, K&N is overrated in these applications.

 

How many miles on your stock catalytic converter? May be plugged killing your mileage. Might be time to change it.

 

The cat is bypassed to a glass pack, the car has a little over 200,000 miles with a new engine put in at 125,000 miles. Would cleaning the injectors help (is it worth the price). I have also heard putting a performance chip in would boost mpg, is this true or are they scams?

The car also has a rough idle I don't know if that factors in here or not

Thanks for the all the help :-]

 

Nope! To reap the benefits of a chip the car needs to be spot on i.e in tune and running properly. To Install a chip will just complicate matter and highlight anything wrong.. you ned to go back to basics, checking timing, valve clearances, Mass Air Flow Meter, plugsset to the correct gap etc etc...

 

poor mpgs fixes:
-cap/rotor
-plugs/wires
-new fluids
-TPS
-IAC valve
-o2's yes plural. no sence in doing one just to leave the other old one in there. and dont skimp on the quality on ANY of the afore mentioned parts. i got a cheap TPS off line and turns out no matter how far you had the throttle open, it only read ~3 percent at any time... and the o2's i spent like 110/ea. please dont try to say i spent too much, either! someone tried telling me this already.. my jeep, my budget!!

ALSO, check filters, both dry and wet. and add some sea foam to gas or right into the TB is good. if ya do, get a buddy to keep rpm's up a bit so it doesnt stall. pour slowly!

 

agreed! ya want more ponies? try freeing up existing ones!!

air/fuel/spark/compression. all these effect potential HP.
-cai and/or bored out TB to like 62mm
-new/better cap/rotor, plugs/wires
-exhaust work
-underdrive pulleys or deleting certain power accesories like ac and ps
-gearing: going to 4.10's or higher, will give you a lot of pep. this gets pricey, especially cause if ya wanna use 4wd , you need equal ratios at each end...
-better cooling. adding a separate B&M tranny cooler is easy and takes the responsibility away from radiator.

idk, my .02!

 

The rough idle is the biggest clue. You have a misfire and you're losing raw fuel out the tailpipe. Complete tune up and a compression test should be done.

 

does it exhibit any specific isses like popping at manifold, or hesitating, or stalling? manifold popping (and poss accompanied by a lot of intake sucking) will indicate a dead lean mix. if so go right to fuel tank and instect filter and pump. if not, then maybe PCM??

 

Wow, just wow

I really hope to god you weren't serious about deleting the PS system.

 

This is your best shot so far, start from the idle and go from there. Try cleaning your injectors (soak them in some carb cleaner) as well as cleaning up your idle control valve on the back of the TB, both very simple and if they don't work then you can move on from there.

 

Get that puppy tuned and running well. I keep mine well tuned and maintained, that and I use non ethanol gas now in all my vehicles.

With non ethanol gas I consistently get 50-60 miles further on a tank of gas driving round town in the hills of NE Tenn in my GC 4.0L. That's an extra 2-3 mpg over that 10% ethanol crap. Yeah it costs a bit more, usually about 7 to 10 cents a gallon or about $2 a tank but for that extra $2 I get mostly an extra 50 miles or better on a tankful.
10% ethanol gas here is $3/gal so that extra $2 I pay on a tank of non ethanol gas equals about 2/3 of a gallon of 10% ethanol gas.
We all know, there aint no way in hell a GC 4.0L is gonna go 50+ miles on 2/3 of a gallon of gas. At 16mpg around town which is what i used to get on ethanol gas it would take an extra 3+ gallons @ $3/gal or basically $10 to go that extra 50+ miles so I save $8 a tank which for me is about $35/month or about $400/year.

 

I have found one o2 sensor that's beside the oil pan and front diff, from my understanding there is another one more up stream but I can't seem to find it could any one tell me were its at. Thanks