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6-8 mpg on 4 cyl

2K views 26 replies 13 participants last post by  bluedeval03 
#1 · (Edited)
'90 YJ 165k, 2.5L, AX15, 4.11's and stock axles, no catalytic converter, 2nd owner, motor rebuilt about 125k. Jeep has always gone from full to empty in 110 miles, 14.5 gal tank, has been the same from stock to what it is today.

Has anyone removed the catalytic and had power loss/fuel mileages loss, and decided to put one back on??

New plugs, wires, ICM (part the coil sits in) Any thoughts and ideas would be greatly appreciated. :confused:
 
#4 ·
Buddy of mine has a 97 TJ with a 4 banger and got around the same 7-8 mpg with 4.10s both with 31"s and then 33"s...I swapped in a 4.0 inline six into his for him with an AX15 and it is now getting around 18 mpg or a little better with the 4.10s and 33"s...Big improvement and compared to that piece of junk 4 cyl it feels like a little torque monster by comparison with much better mpg's..
 
#5 ·
Is it throwing a code? When I was still finalizing my exhaust on my TJ, the missing O2 sensor caused the computer to push too much fuel into the engine, getting around 9mpg. Put the O2 and cat back on, 14 MPG on 37s and full width 3/4tons.
 
#15 · (Edited)
Im getting better than that with my 4cyl YJ on fullwidth, SOA, 5.13's, and 37's PBR's and 138ooo miles...I can drive at about 60-65 in 4th if the wind is blowing hard ( which it always is here)...mine is a 95, so its fuel injected..I guess yours is not?...If it were me, Id get plugs ( and make sure the gap is right), wires, fuel filter, Id make a cold air intake for it (it way cheaper to part one to together from vatozone than to buy a kit), and I would try to make the exhaust as straight and free flowing as possiable( like add a flow master or something and rework the pipe unde the engine)...I kept the CAT on mine, Someone once told me these engines need back pressure to run efficiently...That may be an old wives tale, but Im happy with what I can do with it at the moment...
 
#17 ·
finally got to the bottom of my issue. I replaced the MAP sensor, and it drives like a new jeep. Got my power back, even able to use 5th gear up small grades without downshifting. No more gas pedal to the floor in 4th gear just to attempt to maintain 55mph. Was able to drive any where from 55-70mph without any problems.

I hope this will help someone else with similar issues.
 
#19 ·
I am on my way to doing the v8 swap. So far I have a rebuilt 700r4 w/205 ( will reuse my 231 since I already have the sye on it and save the 205) I have a carbed 350 on the way, still waiting for the guy to get it out. Leaning towards the JB conversions adaptor, can't make up my mind between them or the Novak set up. Seems like the novak set up is more. I already have a tuck pan installed, so that will accept my motor/tranny swap. Still waiting to heal up enough to go pick up an 8.8 rear end.

My goal is to end up on 38's, able to drive it there and back and be dependable.
 
#20 ·
1995 w/184,000 4cly with 33's & 4.56's I get between 10-14mpg & can drive @ 80-85mph

I did some mods to the engine:
reclocked MAP sensor
MSD blaster coil
4.0 throttle body w/spacer
8mm wires
Platinum 4 plugs
Polished & ported head
Adjustable fuel pressure regulator
24lb. Fuel Injector
Free flow exhaust

Every mod I did made a difference in preformance

You can call them POS & whatever. But, the 4cyl is a good engine & will last a LONG time. I put mine threw the ringer, back again & my foot is heavy. Still running like a champ @ 180K+ miles. I have rebuilt the tranny 2 times & about to do it again. :flipoff2:
 
#21 ·
1995 w/184,000 4cly with 33's & 4.56's I get between 10-14mpg & can drive @ 80-85mph

I did some mods to the engine:
reclocked MAP sensor
MSD blaster coil
4.0 throttle body w/spacer
8mm wires
Platinum 4 plugs
Polished & ported head
Adjustable fuel pressure regulator
24lb. Fuel Injector
Free flow exhaust

all those mods are great for the 91 up 4cyl. 90 back uses the TBI set up.
 
#23 · (Edited)
I am definitely open for suggestions. I haven't found anything for it. At one time there was aftermarket header, no longer available. Every search I have done has come up applicable to 91 up.

from the searches I have done on Pirate, I haven't seen anything good come out of this motor to spend the money. What some had done after head work, motor, port/polishing, numbers weren't any better than the 4.o.
 
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