PINIT 141

Hey guys, I have a 98 ZJ with the i6. 4.5 lift and 31s, the thing feels like it has no power. really have to push the pedal to get it moving. and im assuming 12 mpg isnt normal? what are a few cheap mods i can do to get a tad more power. im going to put 4:10 gears in it aslo. Thanks.

RatchetMaster10

The 12mpg is a little low. But I'm running the same set up and get about 15mpg. I would start with the basics and pull your spark plugs and see what condition they are in. It's amazing what bad spark plugs or ignition components can do.

jnicewan

The 4.0 is a turd and it only gets worse when lifting and getting larger tires. You should get better mileage though so that may be an indicator of it being out of tune. I get around 15mpg with most of it being city mileage. The 4.10's would help a little but I would start witht he basics, like filters, plugs, wires cap, rotor and such. Also clean the injectors or at least run a bottle or 2 if good inj cleaner in the tank.

RatchetMaster10

Seafoam works good to run thru the tank to clean the fuel system. Also you can run about 1/3 a pint of seafoam into the vacuum line off the brake booster to clean any carbon build up out

PINIT 141

Thanks guys. pulled the air filter and it was pretty nasty. ill throw new plugs and wires on it as well as the cap and rotor bug. i already ran the sea foam through the tank and intake not too long ago.

CherokeeCountry

Keep in mind, you drive a ZJ, the gross vehicle weight is also a lot higher than that of the cherokee's guys. But agreed, start with general maintenance to make sure it's running proper. Gears will definitely help you though with getting the heavier vehicle moving.

PINIT 141

yeah that is on my mind, my girlfriend drives a XJ two door and it gets like 18 mpg with 35s!

nv6r

I have heard the 4.0l called a lot of things, but never a turd! I find they have way more low end power than most V8s, and have more HP than some, too. My slightly modded XJ does 0-60 in about 7.5-secs, which I would not call a turd!
If a 4.0l is lacking for power, then I would say there is something wrong with it!

94zjdriver

Well I run a 94 grand 5.2 auto no lift and get 16 city and a little better on road.. I put in new plugs, changed out the fan to and efan from a Cont mark VIII and did a general clean up of engine.. I don't keep my foot out of it at all... ask my friends.. LOL

PINIT 141

Put Accel ignition on it, coil too. new air filter and a TB spacer. I can tell a power gain on bottom end. my MPGs are slowly rising also.

DeepSouthXJ

What gear ratio are you running now? If you are under 3.73s, you probably need to go up on your gear ratio to pull the taller tires.
3.73s should pull 31s easy enough. I wouldn't spend the dough going from 3.73s to 4.10s looking for better low end power/response unless you plan on 33s in the future.
Sounds like you are on the right track doing basic maintenance getting the engine back up to proper tune. I'd go with a set of headers and a good flowing exhaust next. Make sure your fuel system is in top condition. There are several options on replacement injectors that would increase your pulling power and often help with economy if you drive it right.
Here's one option if you absolutely need to replace your injectors. These things are the ticket for power and economy:
http://www.precisionautoinjectors.co...1&categoryId=3

PINIT 141

3.55s now. yes i plan on going to a bigger tire size. and wow those injectors seem like the thing to do. Thanks!

DeepSouthXJ

That's part of the problem. 3.55s work great with 235s or 30s, as long as you're not towing anything heavy. You aren't gonna have the snappy response with the 31s and 3.55s that you have with the stock tire size.
You found some lost power already with a basic tune up using upgraded performance type parts. I believe your next step is a new fuel filter and injector cleaner.
Keep working on bringing the efficiency of the engine up and you'll gain a good bit of throttle response and fuel economy to boot. 4.10s will be a noticeable jump from 3.55s, then you'll be begging for 33s to get the RPMs back where you are used to seeing them. Lol.
I'm on the verge of getting a new set of injectors for mine and those from Precision caught my attention. Just don't have that kind of jack to kick around right now. I might start a thread asking for two more members to go in with to get the $40 discount when you buy three sets. You interested?
I've done the header and flowmaster. Still doing routine maintenance. Will get there eventually.

PINIT 141

been trying to sell my brand new 31s for a few weeks now to get 33s. 4.10s will go in soon. and after i saw those injectors i did alot of re search and found out that you can use other ones that are direct fit out of other cars.

PINIT 141

Alright, i have had time to drive it around and with the up grades i did (accel kit ,throttle body spacer) THE GAS MILEAGE IS DROPPING. I went from 12.6 to 11.9 in about 10 miles of driving!! WTH is going on. I put a bumper on the front. about 120lbs with the winch. I dont think that would drop it alot though.