Ive read alot of conflicting information on gains from replacing the intake manifold with 99+ for 1996 4.0. But I havnt seen any exact science going on besides some dynos for already non stock engines. My question is this: Is there any intake manifolds that can be purchased NEW available that I should be looking at more specifically. Not so much worried about huge gains (bro) as much as I am about improving MPG and just replacing the parts one by one to extend the life of my 96. It only has 103k on it so it has plenty of life still in it but I figure id get the ball rolling now on replacing stuff and tuning it up a bit. Im a noob when it comes to jeeps so any other info like any changes to CPU or anything like that would be appreciated. Ordering online is fine with me and installation will be going through a VERY trusted shop that ive been going to for years.

Thank you for your time guys, ive gotten alot of help just by reading the various posts.

 

I don't have any solid info on the manifolds, but a suggestion to consider cost vs. benefit. Replacing a manifold is a big job. Will the benefit of a slightly better manifold repay that effort? I very much doubt it. Now, if my 96's manifold were cracked, I'd certainly try to replace it with a new one, but no way would I invest that much effort for the small gains of the newer manifold.

There was a thread on here that ran actively for several years about how to get better mileage. After many hundreds of posts, and a lot of very dedicated, thoughtful work by the guy who started the thread, he was getting almost exactly the same mileage as me, with a box stock Cherokee.

I have a 50 mile commute, one way. When I was deciding on a commute vehicle to replace my truck, of course I looked at econo-boxes for the MPG. I really wanted a Cherokee, but that mileage..... Then I just did the math. Getting the Cherokee was going to cost me under $1000 per year more than an econobox, and I wouldn't have 4WD (I live in snow country). That was back when gas was pushing $4 per gallon around here. I got the Cherokee.

I would not spend a lot of effort in trying to eke out a few MPG. These things have all the aerodynamic qualities of a brick. It's trying to make a silk purse out of a sow's ear.

Your personal driving habits will make far more difference than an intake manifold.

 

I agree with everything you said. I have the money to burn and plus the little extra MPG actually adds up for my commute. My process of thinking was more along the lines of "im probably going to pass this down to my kid one day" so replacing any/all based on funds (unless extremely over the top) isnt a big deal for me. Plus, not to mention, the guys who do my repairs are literally a "and a pack of beer" kinda dudes who know their way around jeeps well. This info is more for myself to know and to know a ballpark idea of what id be geting into. Im already looking into a better fuel injection path and whatever performance add ons I can get to improve a little at a time. If Im getting close to 18-19 MPG then im happy. right now im pushing 12-13. I put 20 bucks in and get around 75ish if i drive like a grandma, but I dont always drive like a grandma. Also, side note, have any idea about dipping gas gauge? I notice I dont get an accurate rep of how much fuel I have unless the jeep is stationary for a couple of mins. And thanks for your input my friend, I appreciate any and all info/opinions I get, even if they go against my own. After this next tune up, im gonna go for a complete exhaust system + headers so finding a good one thats cali compliant is a whole other shebang.

 

actually. just found a pretty extensive testing thread and it had a 26HP gain, but little to no fuel economy increase. I think im just gonna go with your advice on this one and just keep my eye on other things.

 

You know what made the biggest difference for me (given that all systems are operating correctly)?

Dropping into 3rd gear going over the mountains, instead of leaving it in 4th. The average speed is such that it kept hunting back and forth between 3rd and 4th, up and down, up and down. When I plunked it into 3rd and left it there until I got down the other side, I picked up an average of 2 MPG. That's a pretty big increase for free.