Bought a new to me TJ Mpg&tune up ?s

Jimmytj

Member
Joined
Jul 12, 2012
Location
Fuquay Varina, NC
So I sold my 98 xj 3 in lift 33s on stock gears and bought a 97 TJ with 4.5 in lifts 35s and the po had it reheated to 410s in the d30 and 8.8 he had built at ecgs. It's a nice moderately built rig and was done right. Ill be dd it till I can find a smaller car to drive as well. I believe it has the 15 gallon tank. It's a 4.0 I6 with the 3 speed auto and has 117k miles. I know it's a Jeep but from full to 3/4 of a tank I'm only seeing about 40 miles. The oil was just recently changed but maybe it needs a tune up? I have a new upstream o2 that I bought for my xj should I throw that in? It has a banks intake,header,and exhaust with a tb spacer. It's not a dog to drive and drives like my xj as far as speed. What should I do ? Is this normal?
 
the larger 19 gal tank will bolt right in.

However, you're getting probably 10-12 MPG at that rate. Is this mostly mixed and city driving? if so, it's normal.
With 35's, I wouldn't expect anymore than 15 MPG.
The cherokee and Grand cherokee got better MPG with the same engine, trans, axles than a wrangler.
 
I've heard the 15 and 19 are the same tank 15 has a longer breather hose I believe. It seems to go slower after the first quarter tank so I guess ill just wait and see. Po said he got 13-15 mpg out of it but I have my doubts.
 
The tanks are the same. The filler tube on the 19 gallon is shorter, so it lets more fuel in the tank before it comes back up the breather side.

The best I've ever gotten on a tank was about 150 miles on 15 gallons. That's with 32s, 4.10s, a 4.0 and AX15. I'd say that anything better than that is gravy.
 
One more thing to consider is your cruising RPM. Your TJ with a 32RH auto will be turning quite a few more RPMs at a given speed than a comparable XJ or even ZJ with an overdrive automatic. Your TJ is heavier, less aerodynamic and has a non-OD tranny. Anything over 10-12 is good.
Before you spend money on o2 sensors, have someone scan them and see if they are functioning correctly. The upstream should switch from about .3-.9 volts at idle. The downstream should not switch, but rather stay within .1v after it enters closed loop. Plugs should only be the OEM suggested ones, which are Champion RC12LYC IIRC.
 
Well guys when I went to fill up I had used 10 gallons and went 158 miles that's almost 16 mpg on 35s guess I can't ask for much better than that I'm happy thanks for the help.
 
I did drive like a grandma most of the time.
 
Jimmyxj said:
Well guys when I went to fill up I had used 10 gallons and went 158 miles that's almost 16 mpg on 35s guess I can't ask for much better than that I'm happy thanks for the help.
Click to expand...

Thats very good. I used to get 14-15 in my 1 ton TJ on 35's.
 
That's what I was thinking. I'm impressed, and the 4.10s actually do great for a dd.
 
Back
Top