1994 4.0L HO Tuning

[BlackStick]

I just bought my first jeep about a month ago and it's great in every way except for power. I bought this jeep after my little brother totaled my 1998 Mercury Mountaineer with the 5.0L V8 that got 350+ HP after modifications. Now I feel like I have 6 squirrels pulling me around. I have never tuned a motor before, so be specific. What can I do to give it some balls?

 

[Itchee96]

Its a straight 6. It will never have the HP your V8 had, but the torque will make up for it. Change the plugs, get a cold air intake(unless you plan on snorkeling with the jeep), and regear it. If all else fails, slap a turbo or supercharger on it!

You are comparing apples to oranges in relation to power.

 

[BlackStick]

I knew that it wasn't going to match the V8, but the 1994 YJ weighs about half as much as the 1998 Mountaineer. My objective is to be able to spin the tires on pavement. It is just not possible now. Any other tips?

 

[Bounty__Hunter]

Your tires are about 3" larger than stock, so regearing the axles a little lower will help greatly. If you're at 3.07 in the axles, consider a set of stock 4banger axles with 3.73 or 4.10 gears, cheapest and easiest route to go.

Replacing the stock airbox and airtube with a performance airtube and conical filter will help quite a bit.

Consider a Firepower ignition kit from 4.0 Firepower Ignition Kit and open the plug gap up to .065".

Then there's performance camshafts and possibly a valvespring change, Hesco Inc. - High Performance Engine Service is a good source.

I have 62mm performance throttle bodies available if you're interested, they flow a lot more than the stock 55mm. In addition, the taper below the throttle plate found in stock throttle bodies is removed which greatly improves throttle response off the line. Only $95 plus a refundable core charge. Email me at bountyhunter AT sija.org if you're interested.

Exhaust header wouldn't hurt, as well as having the head ported and polished.

Once you start tinkering with the power you can consider a wide-band o2 sensor to keep track of the air/fuel ratio, and google 'adjustable map sensor' so you can tinker with the ratio to compensate for the mods and get the most gains.

Happy tuning.

 

[palehawaiian]

I knew that it wasn't going to match the V8, but the 1994 YJ weighs about half as much as the 1998 Mountaineer. My objective is to be able to spin the tires on pavement. It is just not possible now. Any other tips?

Port and polish the head, make sure they "port match" your head. Should run you about 400 bucks ... then get a cold air intake, dummie O2 sensors and a nice flowmaster cat back system and a newer highflow cat or trash the cat alltogether if you dont need to worry about emmisions.

That should get your tires chirping nicely

And btw my jeep spins its tires every time it see's that "spin tires on pavement" signs on every corner. DAMN MY TIRES GO QUICK

 

[palehawaiian]

oh yeah headers cant forget the headers... rugged ridge makes a nice set for the buget buyer, they can be had for like 179 or around there if you look a lil

 

[cidd]

hows about a littel nitrous boost for it :bomb: that will give it an extra 100 HP for a second or two :shades:

 

[jfrabat]

You can also go with Mustang injectors for a bit better fuel atomization... And dont forget the eFan swap. I did that to my 2.5L, and you could feel the difference...

 

[wrangler76]

The only true cure for your affliction would be a v8 swap.... everything else will be dumping lots of money for minor return.

 

[Sine Deviance]

The only true cure for your affliction would be a v8 swap.... everything else will be dumping lots of money for minor return.

What he said.

Simply put, if you want V8 power, you're gonna have to swap in a V8. It'll PROBABLY cost more than souping up the 4.0L and it will require some fabwork but it's been proven as a good idea more times than you can count.

A good swap for short-wheelbase Jeeps is the Chevy 350 smallblock w/ a TH350 or TH400 (TH350 is compact. TH400 is big but much stronger.) If you get a modern smallblock with EFI and it came out of something halfway decent you'll be pushing close to 300hp and as much torque as soon as you finish the swap, and both the TH350 and the TH400 are practically bulletproof. Not only that, smallblocks and the above mentioned transmissions are plentiful and relatively cheap, especially if you pull em' from a junkyard (I've seen a running set in good shape go for less than $500.)

And that's not even mentioning the tuning potential with a smallblock. $500 more could easily put you way over 400hp. In a Jeep, that's insane. The TH400 will more than be able to handle it without any extra mods.

You can get an adapter so that the new transmission will bolt up to your existing transfer case. You most likely have an NP231 xcase, and that will work fine for whatever you want to do. If your Jeep is a manual (AX-15 transmission) and you want to keep it a manual you can also get adapters to mate the engine with that transmission. This is also fine, the AX-15 is pretty strong; however, I'd still go with one of the TH variants on principle. Check this out: http://www.novak-adapt.com