is the 4.0L just a FI 258?

[raser13]

Quick set of questions for the well knowing masses. I'm going to be putting a AMC 258 i6 / 4.2l back into my CJ5 . It's replacing a problematic chevy 350. But anyways, i was talking to a few guys at our local amc club meeting about it. And they were wondering why i didn't add the 4.0L FI while i was at it. According to them it's the same engine just with the FI added. Is that true? I noted that none of them was running FI on their cars. If the 4.0L is the same what all would be needed to "upgrade" to the FI? The car the AMC 258 i6 / 4.2l came out of was an 83 concord wagon and the carb had a lot of that vac and electronic control crud they had back then. So one way or another I'm going to replace the carb set up. Either I'm going to go simpler, or i can go for the reliability of the 4.0L injection if it matches up. I do have a junk yard nearby that has a jeep with a 4.0 that has an intact engine and harness that they'll give me a deal on. So any info and help in this matter would be greatly apreciated. Thanms guys.

 

[Kane]

The 4.0 is based off the AMC 258 i6 / 4.2l architecture. The blocks are almost the same and the 4.0 is basically a short stroke AMC 258 i6 / 4.2l . This is why the 4.0 guys can put in a AMC 258 i6 / 4.2l crank and then call theirs a stroker. The heads from the 4.0 fit just fine but do need to water jackets to be blocked off that the AMC 258 i6 / 4.2l will not use. Other than that it is a worthy swap that I plan to do to mine. if you go to fuel injection then you need the computer harness, installation of a high pressure fuel pump and lines and then deal with wiring and converting all that in. The carb is a simple way to go but the real benefits of the head conversion shine through with the fuel injection.

 

[raser13]

Would i need to swap heads? Shouldn't i just need to swap intakes? Every image I've seen it looks like the injector rail plugs into the intake. I'll have to admit that i didn't look that close when i was at the junkyard.

 

[Kane]

Would i need to swap heads? Shouldn't i just need to swap intakes? Every image I've seen it looks like the injector rail plugs into the intake. I'll have to admit that i didn't look that close when i was at the junkyard.

The 4.0 liter head flows much better than the AMC 258 i6 / 4.2l so it makes sense to swap both.

 

[Torxhead]

I would suggest installing the complete 4.0 if you can do the computer hook up. Might have to do some chip work here.

 

[raser13]

The lower end of the 4.0 is why the jeeps there in the first place. I'll have to get the head looked at to make sure it's good if i decide to do this. Would there be any thing else off the motor that i'd have to have? I know I'll have to snag all the sensors.

 

[raser13]

The 4.0 liter head flows much better than the AMC 258 i6 / 4.2l so it makes sense to swap both.

Sounds like it would be smart to switch to the 4.0 head regardless of weather i do the full upgrade or not. Or is the better flow not worth the effort?

 

[Jimbos76cj]

The 4.0 head bumps up the compression on the AMC 258 i6 / 4.2l block. You will need to do a little bit of modification on the 4.0 with the water jackets. You also need to do a bit of grinding and modifying the AMC 258 i6 / 4.2l intake which is easy to do.

Thisguyyouknow from here was redoing the 4.0 harness for a conversion. Im not sure if he still is or not. As mentioned already you need to change to a electric fuel pump and replace your stock lines.

You will also need to reuse the 4.0 Header. They are different from a AMC 258 i6 / 4.2l manifold.

If reusing the entire 4.0 it should be straight forward, you will get more power and better fuel economy.

Back to the head I would buy a clearwater 4.0 head. They may seem a little bit pricey but once you add up the cost of getting a JY head, having it cleaned and properly checked it would come to more then getting a ready to bolt on head.

 

[Neuner]

There is a 4.0 head on a AMC 258 i6 / 4.2l swap thread on here that went into good detail and probably answers most of your questions. It was done with the OBDI system. http://www.jeep-cj.com/forums/f2/4-0-swap-w-pictures-22401/

What year and make is the donor Jeep with the 4.0? It can make a difference.

Since you are in Missouri, you will have a tougher time than others passing inspections. Check out the California 4.0 OBDII Swap Thread by SLO_Ken on another site to see what you would have to do to comply. This has been a good guide and reference for others, regardless of the OBD version, on what it takes to pass.

BTW, the 4.0 has different internals but the exterior is still cast/machined the same. It still has the same mounting holes for the engine mounts as the AMC 258 i6 / 4.2l with exception to one odd M12 which I think is on the drivers side. Bellhousing mounts are the same as well for the later models. Not sure on how they're different than the earlier models if at all.

 

[raser13]

No problems with inspections here in Mo. If it's older than 1990 it only needs safty. So 90 on back is a free for all. I'll have to check the year on the donor. I didn't think it would make much of a difference.

 

[tinman]

At the very least, do the 4.0 head, maybe the easiest and cheapest 50 HP you can get. The complete heads from Hesco or clearwater are easiest (and just fine), but if you don't mind doing a little leg work, you can save a pretty good amount. I think I was into my junkyard head $400 or less, and you could probably do better than that.

It's pretty much like Jimbos76cj said, modify a few things here and there, and you're good. Now, if you want to go with FI, it gets a little more complicated, but still very doable.

 

[Neuner]

I didn't think it would make much of a difference.

This is information from my notes while doing internet research before the swap. I didn't validate it but found quite a few with the same information. Who says it didn't originate from the same person?

ZJ: '93-98 (Gen 01)
WJ: '99-04 (Gen 02)
YJ: '87-95 (Gen 01)
TJ: '97-06 (Gen 02)

OBDI - 91-95 XJ, Wranglers, Commanches and Grand Cherokees
OBDII - '96-01 XJ, '97-05 Wrangler and Grand Cherokee

From what I gathered, there is a best performance improvement to EPA regulation ratio with OBDII and Gen 01 engines so I searched for a '96 - '98 XJ or ZJ 4.0. Gen 02 engines have a slight increase in performance but the EPA regulations increased.

Seen swaps with '99+ 4.0's but care has to be taken in selecting one with the right casting number. Appears there were a lot with bad casts and therefore cracked heads. I *think* it was '00 or '01. Saw a lot of cheap 4.0s for that year with replaced heads.

Got mine from a '98 ZJ with an automatic and found a '98 XJ manual PCM for it.