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Official 4.0 swap thread

179K views 466 replies 98 participants last post by  locohosa 
#1 ·
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.
Flywheel/flexplate
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 herehttp://www.hesco.us/shop.asp?action=details&inventoryID=43098&catId=7902 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.
Cooling
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
Wiring
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.
 
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#334 ·
I was impressed how quickly it picked a prime. I think I'm getting more than 35# of pressure at the fuel rail. I don't remember what the desirable pressure is off the top of my head...
 
#336 ·
Something like that. I know when I purged the relief valve it shot across the engine bay! That was AFTER I discovered I had connected the pressure to the return and vice-versa!!! Couldn't understand why I wasn't getting fuel! Thought my fuel rail was bad!
 
#340 ·
That looks an awful lot like the second picture in my post above... except the connector may be different.

here's another image from a different angle


If you can handle cutting and splicing the old connector onto a new sensor (if needed), I'd say go with an aftermarket sensor. They will perform the same. :2thumbsup:
 
#344 ·
yeah, that's the one!!


Another comment. I've read on the XJ and TJ forums that sometimes the aftermarket CPS sensors don't want to work properly. When they replace them with an OEM sensor from the dealer, the work perfectly.
 
#346 ·
Has anyone had problems with the clutch not working after the swap? I either slept through that part of this swap, or I skipped over it, but I never saw where anyone had this problem. My clutch fork is hitting the back edge of the square window in the bellhousing. In other words, you can't depress the clutch pedal far enough to activate the clutch. The reason for this is the 4.0 flywheel is 400/1000s thinner than the 258 flywheel. This allows the throwout bearing to sit farther back. I have searched for a longer TO bearing, but to no avail. Novak makes one, but they are retooling, and they are at least two weeks away before running them. The other option is an adjustable pivot ball.

Where did I go wrong? What did you guys do to avoid this problem?

We are using an XJ 4.0, XJ manual flywheel, modified 258 bellhousing (for CPS), T18 tranny, diaphragm clutch set.
 
#347 ·
My initial thought is that something is missing. That small of a variation in the thickness of the flywheel should not translate to the clutch fork hitting, and meeting a longer throwout bearing.

Is it possible that you either forgot to put in the pivot ball behind the clutch fork, or it fell out? I usually use JB Weld, or epoxy, to hold them in place while I am positioning everything. It doesn't last forever, but by the time the epoxy lets go, the ball is firmly seated behind the clutch fork and won't go anywhere.

As far as getting a larger throw out bearing, take your current throwout, bring it to the parts store, and find something a little longer. They do make them for various applications.

I am running a T176 and a 4.0 flywheel, and had no issues.
 
#348 ·
My initial thought is that something is missing. That small of a variation in the thickness of the flywheel should not translate to the clutch fork hitting, and meeting a longer throwout bearing.

Is it possible that you either forgot to put in the pivot ball behind the clutch fork, or it fell out? I usually use JB Weld, or epoxy, to hold them in place while I am positioning everything. It doesn't last forever, but by the time the epoxy lets go, the ball is firmly seated behind the clutch fork and won't go anywhere.

As far as getting a larger throw out bearing, take your current throwout, bring it to the parts store, and find something a little longer. They do make them for various applications.

I am running a T176 and a 4.0 flywheel, and had no issues.
Thanks, Nelson. The pivot ball is in place, and I have no explanation for this malady! There is more to this story, but I won't post it up here. It can be read in Clay's Build Thread... the last few pages. Going with an adjustable ball stud. I will keep ya'll posted.
 
#357 ·
#356 ·
I agree. I used a new Luk flywheel when I did mine a few months ago. I definitely think I would have noticed almost 1/2" difference in thickness. That's close to 30%!
 
#358 ·
Gigemags05 said:
I completed this swap using the hesco cps relocation kit. Now, I think my cps is going out. Does anyone know if I can use an after market cps from the parts store or do I have to replace it with a hesco cps?
I replaced the cps and am still having the issue. The jeep starts and runs fine then suddenly dies.

It looks like its throwing code 73 and 75, but I can't find those anywhere for a 1992 4.0

I'm at a complete loss.
 
#359 ·
I had a similar problem with a friends rate down the trail the other day. He has an early 90's XJ. The problem ended up being the ballast resistor. Once we bypassed it, he had no other problems.

I eliminated the ballast resistor when I send out my wiring harness, but if for some reason you kept yours ( and you used an XJ harness), that may be the problem.
 
#361 ·
I spoke with the people at hesco and they suggested it might be the IAC valve so I changed it with no luck.

I reset the computer and its throwing
12
33
35
36
55

The only one that could really effect me is 35, which is:

35 Cooling fan relay circuit open or shorted
OR
35 idle switch motor fault - check connections

But I've checked all connections and they seem fine.

Should it be throwing codes 33 and 36 even though I have no ac or turbo?

The gentleman at hesco says he thinks I might have a bad pcm because its throwing codes that don't apply to my jeep. He said if I have a functioning speed sensor that my computer should learn. I assume my speed sensor is functioning. It's brand new. If it wasn't functioning would the speedometer still work?

Have any of you had issues with the original 4.0 pcm not working properly after the swap?

I just don't want to drop $400 on the hesco pcm if its not necessary.
 
#362 ·
35 is a cooling relay switch, which I don't have connected in mine either, as I have my own electric fan control wired up. This will show up when I pull codes on mine. This makes me think you're using some form of XJ harness/PCM, because the wranglers never had Electric fans.

33 shows up on mine as well, and I don't have ac. This shows up on most YJ and XJ's iI have pulled codes from, and many of them don't have air conditioning.

I've never seen 36 come up before, but I don't think that it's a problem. I classify that along with the air conditioning code that came up.

Even if you are not throwing a check engine light, there are still codes in the system if you check them. My jeep as it stands right now, is running fine, even though the above codes would show up if I decided to pull them.


How long is your jeep running before it dies? Is it running for a few seconds? A few minutes? Half an hour? At full operating temperature? When it's cold?

I'm typing this on my phone right now, so I can't look back through the thread to see if you've already answered it. If you have, I apologize for asking again.
 
#364 ·
Okay, that helps a little:


I had a similar problem about two months after my swap. I ended up tracing it back to the coolant temperature sensor. Once I replaced that, the problem went away. It's a cheap part, so it maybe worth a try.

If you do go the PCM route, there is no need to spend $400 to get the Hesco unit. I would find someone that sells used Jeep parts in your area, and see if they have one. I got mine for something like $40. For what it's worth, all of the "new" units out there are really rebuilt factory units, or so I am told.
 
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