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supraman1990 10-17-2007 08:33 PM

Official 4.0 swap thread
Well, I saw that their was an AMC V8 thread, so I figured I would try and start a 4.0 swap thread here. Feel free to ask any specific questions you have, as I am sure I will miss some things. Let me know what you think and if thre thread should be a sticky.

Engine mounting
Well, their is some good news here. Your CJ 258 motor mounts will work. You do not need to move any mount brackets, or even change the actual mounts.
Depending on how you plan to mount your CPS (Cam Position Sensor) you may be able to keep your factory 258 stuff, or you might have to get a 4.0 wheel. If you get a CPS relocation kit from HESCO, you can keep the CJ 258 flywheel and starter, it will bolt right on to your 4.0. If you plan on using a CPS in the bellhousing, you need the flywheel and starter for a 4.0 as the CPS reads the tick marks off the 4.0 flywheel.
CPS Options
The two main options for your CPS are the HESCO relocation, and the factory. The HESCO is located here 02 or you can use a sensor in your bellhousing. If your bellhousing wasn't mated to a 4.0 from the factory, don't fear. Novak will drill up your bellhousing to be able to put in a factory CPS sensor for around $75-$100.
Some more good news here. You can use a factory CJ 4.2 radiator for your cooling. Depending on what donor you get your 4.0 out of, yo may have an off-set fan. If your fan is off-set, you just need to get a wrangler water pump, fan, and fan clutch to center it all up. You can also use your factory CJ 4.2 radiator hoses
Here is where everyone freaks out. It is daunting, but once you figure it out, it becomes second nature. It freaked me out at first, but once you have everything laid out it is not difficult. Their are only 5 wires on your Bulkhead that you really need to keep. They are the Check engine light, tach signal, ignition circuit, the fused battery ignition for the CJ fuse panel, and the starter relay. It's as simple as getting a factory manual for your particular harness and finding those wires. Make sure you get one for your exact year, as wiring changed a little every year that I have seen. You can then cut out all the other wires from the bulkhead and cut them off either where they go into a connector or where they go in to a splice. You need to find and splice a few wires in the CJ harness. They are 1.) 12volts from alternator to CJ fuse block (red)
2.) ignition crank wire (blue)
3.) ignition run wire (red with white stripe)
4.) fuel pump wire (not from CJ harness - you need to run this wire yourself based on what fuel pump set-up you use) You can also cut out any headlight wiring you may get. It doesn't really matter if you g e an auto or 5spd harness if you are 5spd. If youg et an auto harness you will just need to put the park sensor wire on a switch that you flip to make the jeep think you are in park or drive to crank. If you just ground this wire the computer will not receive a signal from the MAP sensor and will hardly move.
VSS(Vehicle Speed Sensor)
Their is a debate over if you need a VSS, I plan to get one. It will surely make your Jeep run better, and get better gas mileage. You need to get one with the electrical and mechanical hook up if you plan on using the CJ speedo. One from a 91 YJ will work, and from a late 80's Dodge Dakota.
Fuel Pump
You can do an in-tank, if you get a fuel sending unit from a TBI 4 banger YJ and the actual pump from a MPI 4.0. You will need to figure out wiring up the sending unit to make your gas gauge work, as it is exactly opposite of a CJ sender. You can also go external. That is my personal thought. Most guys that do the swap go with an External E2000 fuel pump. It was used in ford vehicles for many years. You need a pre-pump filter and post-pump filter. The pre-filter can be a standard filter, but the post needs to be a fuel injection rated filter. Also, you MUST have fuel injection rated hose where you use flex line. This stuff is several dollars per foot, but you need it to take the pressure. I also recommend fuel injection hose clamps for all connections. Ideally you need 5/16 line to the rail and for the return, but I think 1/4 on the return will work alright.
Ok guys, this is the gist of it. If I missed anything, feel free to reply asking questions, I will answer them to the best of my ability. This pertains to the OBD1 swap, as that is the one I have experience with. Let me know what you think, and if this should be a sticky.

Chrisfol82 10-17-2007 09:08 PM

One good idea that would work perfectly in this situation is to use a custom fuel injection control computer such as megasquirt.

This would replace the factory computer and probably most of the wiring. You would make your own wiring harness and have complete control over the engine including an electric fan, idle air control solenoid, spark control and pretty much anythign else you could want to control.

No crank position sensor is necessary either for megasquirt so the bellhousing modification and flywheel stuff would not be necessary. This is the setup i have on my 258 right now which is basically a 4.0 from the head up. It may not be the best choice for someone who wants to just plug in a 4.0 and drive it away but for someone who really likes tinkering with their engine and trying new things it can be alot of fun.

And for the price of alot of the adapters and kits that you would need to get the 4.0 computer working the MS system would probably be comprable in price.

supraman1990 10-18-2007 08:06 PM

ANyone interested in this being a sticky? I know it is the most common swap after the V8 swaps.

thantos858 10-18-2007 08:59 PM

Do you have pics? Im interested in options right now since my motor is near its end.

supraman1990 10-18-2007 09:04 PM

Pics of my swap? Unfortunately, no, but I can guide you on part selection somewhat.

Houdini 10-21-2007 09:44 AM

I'm glad this is a sticky! I'm going to stay I6 because it just seems right for me. What I haven't decided yet is to go 4.0 or go 4.2 with FI. If you have a strong 4.2 and do FI is there any advantage to go 4.0? I won't make my decision for 6-12 months so I'm hoping this thread gives me good info to make that decision.

supraman1990 10-21-2007 05:36 PM

4.0 has a little more power than the 4.2 and will rev higher. However, if you have a recently rebuilt and very strong 4.2, I would advise doing a 4.0 head swap with all the FI stuff. It will net you more torque than the 4.0 and the same reliability and FI.

Chrisfol82 10-21-2007 08:18 PM

I agree the 4.2 can be built to be just as powerful if not more powerful than the 4.0. I think my 4.2 has more power than any stock 4.0 ive ridden in.

But a 4.0 can also be built to have more power than a built 4.2 if you do a stroker to the 4.0.

So either one is a pretty good engine. I like my 258 and the only reason i woudl swap to a 4.0 woudl be if i was going to make it into a stroker to get more power than i have with my 4.2

Bubba Ray 10-23-2007 02:55 PM

I would think that the 4.0 head to a 258 would be worth a sticky post.

Rollbar 11-03-2007 10:16 AM

4.2 pistons R bigger then the 4.0. I think the 4.0 is actually 3.90 something, not exactly sure. I have a 4.2 & a 4.0, I like both of them but prefer the 4.2.

I to would like to see a 4.0 head swap sticky.

P.S. Thanks for the info.

gjohnson 11-21-2007 07:17 AM

figured i throw a link of this in here...just more information

sinordev 12-10-2007 09:43 PM

I bought a cheap OBD-II 4.0 with a harness and pcm for an auto. I want to keep my 82 cj7 manual, can I still use the harness and pcm?

supraman1990 12-11-2007 05:12 AM

Yes you can. OBD2 is a little more difficult to wire, and not completely covered by this write up. I'd refer you to in the 4.0 swap section as I'm not great with the OBD2 swap.

stephens_cj5 12-20-2007 11:08 AM

4.0 vs TBI vs Weber Carb
I have found myself in a dilemma about what I want to put in the jeep. I would like to keep it simple and clean but I wold also like a well running motor. I had full intentions of putting the 4.0 head on my 4.2 block but after reading the above requirements I was a little put off. It seems to be alot more involved than I would like. So I am back to doing the research again and consulting those with the experience on these systems. What are the pros and cons from each regarding the parts required for install, performance gains and maint.

I have zero experience with the weber or 4.0 conversion. I did install the Howell TBI on a jeep I had previously and it was great compared to the stock carb, but anything would have been.

Thanks for the input.

supraman1990 12-20-2007 01:18 PM

If you want simplicity, but till want some help with hill climbs and the ability to drive it a little easier, go TBI. However, if you want the best drivability of a modern car and zero chance of flooding on a hill, go with the full 4.0. I wouldn't stay with a carb if my life depended on it. The 4.0 can look to be a daunting task, but it is honestly smple once everything clicks to you. I bet I read 40 or so write-ups before I got everything, but it's rather simple now. My Jeep will probably crank fr the first time in 9 months within the next few weeks, and I honestly don't regret it one bit.

The time now is 11:57 AM.

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