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Topic Review (Newest First)
07-18-2010 04:51 PM
jeepjones The 4cyl engines have a bad habit of snapping off the most rearward exhaust manifold bolt and the exhaust manifold like the 6cyl ones also have a tendency to crack. Removing the Cat might not be the best idea, there is an oxygen sensor upstream and down stream of the cat, if there isn't a temp/oxygen change between the two sensors the ECU (computer) will think that the engine is running in a cold state and will run in a rich fuel mixture constantly which will certainly destroy your fuel mileage not to mention the Check Engine light will stay on. So check the exhaust manifold and bolts,check the entire exhaust system (pipe,muffler,cat) & fix all the leaks. Do a tune up (plugs,wires,cap and rotor) this will help with the mileage situation considerably. If you need a new cat get a High Flow type of cat. But remember the 4cyl is not known to be a power machine so what it lacks is usually made up for in a lower gear and a foot on the floor. And as always it's a Jeep, basically as aerodynamic as a brick.
07-18-2010 04:29 PM
InfernoGirl Just check the stock filter, a dirty filter will really cut back the mpgs. Heck pick one up for $12 from Wally's and swap it, if the original one looks ok, hang on to it for when the new one is trashed. But likely it has to do with the exhaust or cat...
07-18-2010 03:27 PM
Viper5 well for one do you know if you are still on stock gears, or did the PO regear with lift and tire upgrade. if you are still on stock gears that could be the cause for the low mpg. i have a 98 xj on 33's, and when i had the stock gears in there (3.73's i think) i got a whopping 8 city and 10 high way, and that was after i let it warm up. before it got warm i was getting like 4mpg. from what i have researched and read most of the chips don't offer enough to offset the cost. Before you scrap you cat check you local laws and regulations, i know there is about a .5 hp difference between a high flow cat, and no cat. not to mention for an NA vehicle, you're going to want some back pressure for scavenging effect, so free flow exhaust my not optimize performance. i would say for starters i would begin with the usual maintenance, fliters, fluids, plugs, wires, and dizzy. i know a cap change alone on my 4.0l xj netted me a few regained horses.
07-18-2010 03:25 PM
heath840 So am i looking to just replace the air filter or replace the system with like the AEM or K&N systems?

As for the gear i have no idea...how could i check that?

and will removing the catalytic converter actually help me out? i heard that it improved gas mileage to run without it. (in FL we do not have to pass inspections or emissions tests) so it is almost ok.lol
07-18-2010 03:24 PM
Decemp00 When i had my tj, the exhaust pipe came lose where it connects to the manifold. It sounded like a tank and after it was tightened, I could tell a difference in power. x2 on checking out your exhaust.

PS I'm no mechanic so i'm not even sure if my terminology is correct haha
07-18-2010 03:20 PM
InfernoGirl Sounds like you have an exhaust problem somewhere, so check that, make sure the air filter is clean. The most popular consensus is that chips don't really help on the TJ motors. What gears does it have? Gearing will make a difference with maintaining speed, but I thought all 4cyls came with 4:10's, so I'd first investigate the exhaust problems. If it's all mucked up, it will affect your get up and go....
07-18-2010 03:16 PM
heath840
New Jeep New Problems...

First off, I am new to this site and forums in general...bear with me...

I just a bought a 97 TJ with a 2.5in lift and 31 inch tires...it is the 2.5L 4cylinder...

I have noticed a few things that are a bit unsettling...on flat land the fastest this jeep will go is about 55 to 60 mph...theres no need for a 5th gear because shifting into just slows me down...also through the first full tank of gas it has gotten a whopping 11miles a gallon...finally it is loud as hell, sounds like a big old chevy when it is accelerating.

I can handle the noise but i wanted to put that in there in case that may be a part of the problem.

I have been told a chip, and new exhaust system will fix it all, because it may have an exhaust leak, and to ditch the catilitic converter for it just restricts output. basically im asking what does it sound like to you and what can i do to fix it?

any advice will help guys...I thank you in advance...

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