Hey everyone,
I'm hoping to get some feedback from people who have actually done this upgrade, my first concern is if fuel mileage has improved for anyone who has done this and if there are any notable performance gains. If anyone has done this, I would appreciate if someone can let me know all the parts I should need and if someone has a write up, even better.

The topic has been debated about whether upgrading a pre '99 XJ with the modern intake manifold can either harm or enhance your Jeeps performance. I recently acquired my XJ and have been driving it around for a few months now, I put a new engine into it and have been enjoying it thus far. One hard truth that I came to learn is that the Jeep is bad on gas mileage, really bad. Now I know that Jeeps aren't known for their efficiency but after getting 11mpg on a stock XJ, my jaw dropped, I could only imagine what it might be after a lift, tires and extra weight. After some searching I've found people making claims of getting anywhere from 7 to 22mpg with their XJ's, the worse the mileage the more modified the Jeeps typically were, it left me with the feeling that something is up with my Jeep. I believe that my Jeep is capable of better mileage, so I started being mindful of the throttle and installed 12 hole injectors. I was able to gain 3mpg which was great to see.

I plan on traveling long distances with my Jeep which is why I am concerned with its fuel mileage, I'd like better range and I wouldn't mind it being a bit easier on the wallet. I've been searching of ways to further improve this and one good bang for the buck upgrade that I found was updating the intake manifold, with people claiming up to 2mpg improvement. I believe the intake should help my cause and I would like to take my chances. From the scattered information I can find on the internet it seems like the intake upgrade should be fairly straight forward requiring some modifications/changes for a '95, which I have found to include vacuum lines, IAT wiring, fuel line mounting and the p/s pump mounting.

From what I found I believe that all I should need is the Intake manifold and the p/s hardware (I've got an extra gasket and can grab hoses and miscellaneous supplies from work). I intend to buy all available parts new because I'm not a big fan of laboring over old used parts at a JY if I don't have to. From scouring the internet, I believe these should be all the parts that I should need, I'm hoping someone can confirm or add to this:

Parts:
Dorman Intake Manifold
P/S Parts
1. 34202029 bolt-hex f 136c
2. 33002201 bushing-id 114b
3. 4792112 pulley 116e (Normal ZJ idler pulley)
4. 6503230 spacer-bel
5. 53010148 bracket
6. 53010149 sleeve-ten
7. 6503198 bolt

If I update the intake I am also on the fence about installing a Banks header, I installed a new Dorman exhaust manifold with the engine so I may push off the Banks header for now, although for accessibility I would've liked to replace it at the same time. I'd also like to check the integrity of my fuel evaporative system because I wonder if I could be losing fuel that way and it sandbagging my MPG's.

 

Don't waste money on a Banks header or anything else they sell. Get an ATP or APN header for it, Summit Racing sells them.

 

1. What year is your Cherokee ?
2. Automatic or stick ?
3. RWD or 4x4 ?
4. When your kitchen faucet springs a leak do you bust out the tools or call the plummer ??

XJ's have drag coefficient of a brick. There are mods that improve milage for daily driver XJ's but a Cherokee will never ever be a Prius. Many of those mods are the same ones done to give better throttle response and mildly boost torque for trail XJ's.
There is a point, a threshold if you will, where the next step of improvement in power or milage costs as much as the previous steps combined. That point is variable per each individual XJ owner. The math on that can be cheated. Physics can not.

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Thanks for the responses guys!

I'll take a look at those suggested headers.

My Jeep is a 1995, Automatic, 4x4. I fix what I can and call in the professional when needed. As mentioned above, I knew that mileage would be poor, but I was hoping for at least 16mpgs before any upgrades, they were advertised as 20 city and 23 highway after all. I was able to go an extra 30 miles with the injectors alone, that is one 30 minute trip to the next town over for me, and not to mention they would pay for themselves after 15 fill ups. I thought this was great! Just riding the wave and seeing if I can't better this anymore, it's ironic I know to spend money to save less money but it's more for range and a project.

 

Chrysler MPI injected engines feature adaptive memory. Drive it like you stole it for 50 run/ stop cycles and the ECU has self adjusted the program to accommodate the lead foot. Drive it like a miser and it will adjust to that too.

Mods in no particular order: Clean all the grounds, sensors and sensor connections. Good tune up with brass contact cap and rotor. Hotter coil. Good front end alignment. Good tire pressure. 205 degree thermostat. Bored throttle body. Headers. "No dent" down pipe. Cat back exhaust. RV/ Towing/ Torquer grind cam. Roller timing chain, Roller rockers. Good plugs and plug wires. Oil seperator in the CCV line. Synthetic oils and greases. Relocate IAT to the air filter box. Taurus V6 electric fan conversion. Redline Water Wetter. 4 hole or 12 hole injectors and the 49psi fuel pressure regulator it takes to make them work right in OBD Jeeps. Skid plates. Air filter box venturi delete. Rear disc brakes. Alloy wheels. Beyond that it starts getting labor intensive and expensive real quick.

 

We also have cold weather, winter fuel etc right now. Don't jump the gun. Do the tuneup parts mentioned above first, along with ground refreshing.

 

I'll offer my findings on this:

I recently swapped exhaust manifolds several times and developed a leak. I wasn't going to change the gasket each time I put a different manifold on because it was just for testing purposes only. Anyway, once I finally settled on the right one, I ended up with a gasket leak. Unfortunately, though, it was an intake leak at the manifold gasket, so it had to come off again. I decided that since an intake manifold was only $35 from the junkyard I really didn't have anything to lose.

You'll find that if you swap it, that a couple of things don't exactly line up. The hard fuel line under the intake has a mounting tab that bolts to the intake on the 98 and lower, and you'll have to bend it slightly to move it over. The AIT sensor wires have to be extended, and a couple vacuum lines do too. The throttle body bolts right up without issue, and all throttle cables hook up.

After installing it, I didn't hardly notice any difference. Honestly. That is, until I did my first official fill up. It seems that I have gained about 2 mpg from the intake swap. It wasn't until later that I noticed that the idle was so much smoother. I didn't do an ECU reset, so it may have taken a little time for the adaptive learning to trim the fuel levels properly. Where I used to average about 14 to 17 mpg, now I get 16-19 pretty regularly.

Now, I will say that I live where there are some pretty decent hills on the interstate and I've always had to downshift when going to/from work. At 70 mph on 31" tires, I'm probably turning about 2200 rpm. I noticed that I haven't had to down shift to make the hills like I used to. Yeah, the heat/AC shifts to the defrost like all old cars do as I lose vacuum, but I'm not losing speed with the cruise control set at 70 like I used to. So I'm guessing I gained some torque with the equal length runner intake.

One thing to note is that a few years back I installed some DEI self-adhesive heat shield on the under side of my original log intake (it's a 98) and I never once noticed a change in intake temps before or after adding it. There's been some discussion on whether the AIT sensor should go in the manifold or if it should be relocated to before the throttle body. The answer is that it's a quick-acting AIT sensor, and it's not susceptible to heat soak. So adding the $40 worth of DEI reflect-a-gold was useless, and I confirmed that after swapping back to a manifold without it.

Edit:

On the topic of the search for mileage:
-Tune up. Use OE copper Champion plugs, and a quality (doesn't have to be Mopar) brass contact cap and rotor. I like to use the United Motor Products 27625 tune up kit. You can get it from RockAuto.
- 12 hole injectors are snake oil. Many people have gotten negative results from them. You probably gained 3 mpg from just putting clean ones in instead of your old ones. You *might* get better mileage if you send your old ones out for ultrasonic cleaning and reinstall them (when you do the intake swap)
-O2 sensors make a big, big difference in performance and mileage. NTK is the original manufacturer of the XJ O2 sensor, and has been the only one proven to work well. The downstream O2 is only there for catalyst efficiency monitoring. It has zero to do with mileage.
-Clean your intake. Remove the throttle body, clean it out with some throttle/carb cleaner, and reinstall it. Then run the engine without the intake boot on and spray a can of seafoam in the intake while you hold the throttle to about 2k rpm. When the can is done, shut it off. Let it soak for about an hour. Start the engine, let it warm up, and drive the snot out of it. Of course, this works if you start with a dirty intake manifold. If you install a new one you won't have to worry about it. If you do decide to get a used one from a junkyard, shoot some oven cleaner inside it and let it soak for a bit. Hose it out and it'll be like brand new.
-Tire pressure, wheel bearings, u-joints, and anything else that can cause drag will suck mileage.
-If your automatic transmission has funny shift points, do a cable adjustment. That cable controls the line pressure for the AW4, so it has a lot to do with shift points. The other thing that inputs to the shift points is the TPS. Mine tested fine (several times) and I still had a problem where it wanted to hang out in 2nd gear until 3500 rpm under light throttle. I replaced the TPS and it has never been better. Worst part? It never once gave me a TPS code. It's sneaky like that.
-Exhaust manifolds. You really can't go wrong with stock. That ATP one mentioned earlier works great. The banks header... snake oil (in my opinion). You really won't get much out of the fancy headers unless you do a LOT of other supporting mods, so don't blow your money on it.

So I hope this helps. Many people will tell you that "it's a brick, get used to the bad mileage". Mine is lifted 3", has 31" tires, a heavy steel bumper, a winch, 350k miles, I carry tools, a compressor, etc. (you get the picture). That average number I gave you earlier was mixed in-town and highway driving. On trips I can do as much as 21 mpg in my current configuration. When it was stock I got 24 several times. It's not hard to do, you just have some work to do.

 

Some really great feedback here guys, thank you!!
I'm holding off on the intake for now but I do plan on doing it sooner than later. I found that all 4 of my ball joints have play so I went ahead and ordered some heavy duty chromoly ball joints from Alloy USA. In theory this should affect gas mileage but I'm curious to see what the numbers will turn out to be if any change at all, fingers crossed. I also ordered up the 'Screamin' Demon' Ignition coil and ignition kit from Morris. People have made claims of 2 mpgs better with that kit. I'll see how I fair. I do personally believe that the injectors are worth it, although 4 hole injectors are probably just as good tbh. I replaced the engine in December and have about 1,500 miles on it so far, I did all the tune-up stuff then (cap, rotors, plugs, filters etc.) replaced the exhaust manifold (it was cracked big surprise, lol) cleaned the throttle body, washed the o.e. intake with a hot tank parts washer, and LOADS of other things. I'll post my findings when I get around to replacing all these parts for those interested.

 

Thanks RatFink