ive rebuilt it all myself.... I mean, its a full out rebuild with pretty much new everything. The motor is full out machined, new pistons, rings, balanced crank, the whole bit. It runs awesome, like i said its a beast in the city, but out on the freeway its a different story... when i drove to a nearby city, it was constantly floored the whole time, sometimes to maintain 75 i would have to kick it down to 4th and floor it... i don't know if the engine just needs time to break in, or what.... like i said, less then 1,000 miles on the new motor. The only things i haven't replaced are injectors, the coil, map, cps, tps, and idle stepper motor. I think for sure ill get some new injectors, mine are probably full of crap, so maybe its not getting enough fuel to crank out the power, but it still runs amazing around town... so its a mystery haha.

 

try putting some kinda fuel cleaner in your tank

 

ive ran sea foam, and lucas injector cleaner through it..... maybe all that junk is now in the injectors now... who knows? haha

 

How high are the RPMs when you're at top speed?

 

well 75 in fifth gear my rpms are around 2500-2600, and in 4th going 75 its around 3000-3100.

 

I didn't see if you mentioned this earlier, but did you replace the o2 sensors. I had a problem with mine getting terrible mileage on the highway and I struggled to keep it up to speed on the highway. It didn't throw any check engine lights or anything, but after trouble shooting everything I decided to replace the o2 sensor 1. This is the sensor that calculates the air:fuel mixture. It nearly doubled my gas mileage and completely returned my power. If you haven't checked that out give it a try.

 

Sounds like your Jeep's legs are too long, a re-gear will put you up into the RPM range that you would like, but that is spendy.

 

Just to clarify now I am not trying to argue you

but those are the right rpm ranges for his gearing.

It is just so wired it's only 5th geAr...

 

well, i haven't really thought much about my o2 sensor... it was brand new last year, but i guess it could have been damaged in the rebuild. If my o2 sensor was bad though, would i notice it around town? I put on a new tail pipe, and within a couple days it was black, but that was before i put on a knock sensor, if that makes a difference.... What are some other symptoms of a bad o2 sensor? Its something to look in to i guess, is there any good way to test it?

 

I agree, but he seems to think there is a problem. My ZJ tachs out at about 2100RPM @70MPH. I have 30 inch BFGs on it, I also have the 42RE transmission.

 

well, i took it out on the freeway today, it did awesome until after five minutes.... then it started to struggle... i changed the oil in the trans when i rebuilt my motor, i also added some lucas in it, and it shifts TONS better, but could that be causing some parasitic draw somehow? I'm just thinking of everything it could be. Also, my exhaust exits around 2 feet in front of the back axle. it just goes cat, muffler, then a turn down..... could the exhaust heat up the back axle and do something? i am getting a tail pipe put on today. i put on new brakes and rotors a few days ago when i did my ball joints. it does really well until after 5-10 minutes of driving..... the motor doesn't sputter, it still runs great after that time, i just have to give it a 3/4 to full throttle to maintain speed. its really weird, i checked to see if my engine was running rich, its just right.... the o2 sensor works fine. so any ideas?

 

Put a vacuum gauge on the intake manifold and take the Jeep for a long test drive. You should have good strong vacuum at cruise, but if you see the vacuum start to drop at a steady cruise, you may have a clogged cat converter.

 

i got a new exhaust just about an hour ago..... haven't been able to take it back out, i got driving on the freeway on my way home and my s. belt exploded, so as soon as i can ill take it out, and test it.