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The Yeti 06-10-2011 10:12 PM

2.5l to 4.0L Swap.
Hello Guys and Gals, I am about half way through my 2.5L to 4.0L engine swap and am waiting on parts so I decided to do a write up. Enjoy :thumb:

jkaufman_95 06-10-2011 10:17 PM

Where's the write up? Haha why not go to a bigger engine if your gonna swap em

The Yeti 06-10-2011 10:23 PM

Sorry I was getting all my pictures lined up on photobucket will finish in a minute. The only reason I didn't go with a bigger engine was I had a complete donor cherokee that I could get everything I needed from sitting in the garage.

The Yeti 06-10-2011 10:27 PM

I started with a 94 YJ 2.5L 5 speed and am putting a 97 cherokee 4.0l with a 90 cherokee 5 speed. Here are a few pics of pulling the engine.
The 2.5L still in the jeep
I removed the front clip for ease of access and pulled the engine and trans separate
Here is a pic of the jeep in the day light.

The Yeti 06-10-2011 10:32 PM

Sorry for the bad picture quality, It was all done on a cell phone because I don't have a camera. Everything to this point is really all standard issue engine swap. Unbolt the front clip, unhook all the wiring from the firewall and lay it on the engine, unbolt the bellhousing bolt and engine mounts and lift. At this point it was all done in my backyard and I pulled the transmission there too. Afterwards a buddy pulled it to his garage so I could work on it while it was 100 degrees outside.

The Yeti 06-10-2011 10:32 PM

Feel free to ask any questions if I am too vague on any part of the swap.

The Yeti 06-10-2011 10:42 PM

For me the hardest part of this swap has been finding parts and the wiring harness. I took an extra 2.5L wiring harness I had and spliced it with the 4.0L cherokee. The Wrangler harness was a breeze compared to the cherokee harness. The cherokee harness had cruise control and A/C both of which I ditched for this swap. Also on the wrangler wiring harness all the front lights are on a seperate harness where on the cherokee it is in the same as the engine harness. I'm not the best with wiring so I took and striped all the plastic off the wrangler harness and found every wire that went through the firewall and chased it down and saw what it did. I wrote down every wire and wire color that went through the firewall and where it went through the firewall at. I then stripped the cherokee harness and found only the wires that the wrangler already had and wrote them down. The speedo, gas gauge, and fuel pump all are different from cherokee to wrangler so this was addressed. I then spliced all the corresponding wires and we'll see if she starts next week. If anyone wants detailed information on which wires I spliced and what not I can post it on request.
Here is the 2.5L harness
Here is the more of the wrangler harness
Here is a small part of the splicing
Here is what I absolutely knew I didn't need. After it cranks I will end up cleaing up the wiring a little more.

The Yeti 06-10-2011 10:53 PM

The engine came out of a wrecked cherokee that I knew ran. What I didn't know was it had a hole in the oil pan from the wreck. After removing the oil pan to replace it I also found out that the hole was right where the oil pump was and it was destroyed. So I ended up replacing the oil pan with a spare one i had sitting around and ended up putting a high volume Melling oil pump in place of the destroyed one.
Here is a pic of the engine on the stand
I rolled the engine on it's side for easier removal and installation of the oil pan/pump
Here is a pic of the hole in the oil pan.
Here is the chuck missing out of the oil pump. I thought it was a piece of a rod bearing before I saw the oil pump.
The engine had been started with it like that and it broke the teeth off the top of the oil pump that attached to the distributor.

The Yeti 06-10-2011 10:55 PM

Something I forgot to mention earlier. I am using a 91 wiring harness and computer so it all lines up with my OBD1 wiring in the rest of the jeep. I had to swap all of the sensors over to make it work with the older OBDI computer.

The Yeti 06-10-2011 11:04 PM

The reason I am using a different model cherokee transmission than engine is the donor cherokee had an automatic and I got from the flywheel back from a different cherokee because I wanted a manual. One thing I did not know till now is that they changed the pilot bearings. 91 back is different than 92 forward. So my pilot bearing that came with my new clutch kit doesn't fit the 97 crank, it is too big. So I had to have a machine shop mill the outside down some. If you are doing this swap you can order the correct bearing from Novak but for time's sake I just had a machine shop do mine.

The Yeti 11-11-2011 11:11 AM

I finally decided to finish this write up. I ended up not using the wiring harness I had made due to some issues with the lights. What I finally did do was take my 4 cylinder wiring harness and splicing in the extra two injectors. I found this ECU pinout which made this possible. The only difference in ECU pinouts between the 4cylinder and the 6 is the two extra injectors

The Yeti 11-11-2011 11:20 AM

After I got it all wired up correctly the thing still wouldn't start :banghead: It was firing at some crazy times. It would spark erratically for the coil to the dist. but because of the odd timing it wasn't making it through the cap to the plugs. So after a little research I found out that I had the incorrect flywheel in the jeep. They changed the flywheel design. 87-90 had a flywheel with a lot of teeth for the crank position sensor to read and the 91-? had three sets of 4 teeth. So since I was using a 92 computer and electronics the flywheel was throwing the computer completely off. When I got the correct flywheel in it fixed all of these problems.
Here is the 87-90 flywheel.
Here is the 91-? flywheel
Here are the two side by side

The Yeti 11-16-2011 06:24 PM

I also had issues with the clutch not disengaging when I pushed in the clutch pedal. I fought with that for a long time until I finally realized that Autozone had either sold me the wrong pressure plate or that they changed the pressure plates between the years. After having the transmission out 4 times I finally just put the old pressure plate in the jeep and everything worked perfect.

vachondave 01-16-2012 06:30 PM

i have a trouble with my 4.0 swap!!
hi ... i have a jeep yj 1995 2.5 L and i swap to a 4.0 ho yj 1991 .. i take my 2.5 engine harness and i splice to add two wires in main harness for the two additional injector.. i put the yj 1991 4.0 computer .. plug all connector on engine and tranny and when i turn the key to on the check engine light is not on my dash light... the fuel pump dont run at on position or engine start... and i dont have fire... i use the crank sensor of my 2.5 yj 95 with ax-5 on my 4.0 yj 91 with ax-15 its ok ?? the engine harness are the same for 95 and 91 ??

The Yeti 01-16-2012 09:02 PM

I used my 2.5L crank position sensor for my 4.0L and it worked fine. Are your grounds hooked up? The wiring harness comes through the dash in two places did one of them come unplugged? Are all of your fuses and relays good?

guardian262 01-16-2012 10:30 PM

Dave...Normally not having the Check Engine Light or fuel pump activate when first turning the key is a symptom of a bad computer.

It could be that something got crossed in the swap. Did the 4.0 computer come with the motor and did you see it run before dropping it in place of the 2.5?

vachondave 01-20-2012 04:24 PM

i not view the engine run beacuse its not the same guy sold me the engine and the computer .. the harness have a date link connector on left side of firewall .. the connector is ok ... and i have one harness go into dash for rpm oile presure and tachometer and it is connected ... the engine computer for the 91 and the 95 jeep yj are the same ??

88irocz 08-26-2012 11:10 PM

I see its been a while but hows things going with your swap?

tnjeeprider 08-27-2012 03:21 PM

Hey Yeti, where are you at in East TN? I am in Maryille, south of Knoxville. What did you have to do for motor mounts. I heard that there is a kit that allows the 2.5 mounts to be used for a 4.0 but have not found any info on them. If anybody knows if such a kit exsists please PM me with info. Thanks.

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