Engine Swap Info Needed - 1997 2.5L to a 1998 4.0L

Kenster_66

Kenster_66

Remember him when you look at the night sky!
Joined
Oct 8, 2010
Location
NW Greensboro
Hey guys n gals, I having an engine swap done in my 1997 TJ.
Had a 97 2.5L 4cyl, now getting a 98 4.0L 6 cyl.
HOWEVER the wiring harnesses wont mate up.... any suggestions? Thanks in advance!
 
Sign the title on the 4cyl TJ.

Write a check for a 6cyl TJ.

Stolen shamelessly from Jody Treadway, but he's right. I just finished a swap (literally, yesterday) from a 99 4.0 into a 98 2.5L. I had both chassis sitting side-by-side for the swap, and I needed it. The amount of stuff that doesn't transfer over is staggering. Here are a few things to consider:

The steering boxes from 97, 98, and 99 are all different. 98-99, the hoses were the same. 97? Who knows. But you should probably look it up.

You need the motor, transmission, transfer case (at least the input shaft), both driveshafts, the transfer case shifter linkage, the entire engine wiring harness (back to the fuel tank), the ECM, the fuel lines from the rail to the frame, all the engine accessories (all of the AC lines/hoses and the expansion tank), the intake tubing from the throttle body to the airbox, the engine mount brackets that are welded to the donor frame (this was a huge pain). Probably a few other things I'm forgetting.

The steering shaft bracket can be cut off from the 4cyl and moved back on the frame to clear the 6cyl engine mounts.

If the 6cyl TJ had the "smart" keys, you'll need the ignition key, the sensor off the steering column, and the ignition cylinder from the donor, otherwise your donor PCM won't let the truck start.

The vacuum lines from the 6cyl to the 4cyl are similar, but different. You can make the 4cyl ones work, but if you have both vehicles, it's easier just to grab the brake booster hose and the heater vacuum lines from the donor (intake to firewall).

EDIT: Look up the slave cylinder and master cylinder for your 4cyl and compare to the part numbers for the donor vehicle. If they're the same (mine were), you're in good shape. If they're not, you might need more parts. Oh, and REPLACE THE SPRING CLIP in the transmission while you have it out. There's a little clip that holds the clutch pivot arm to the bellhousing on the passenger side. It is literally $3 at the dealership. Both of mine (donor and old trans) were already broken, or broke when I took them apart.

On my swap, there's a "chassis" wiring harness that includes the underhood fuse panel, the rightmost (PS-most) ECM plug, and the bundle of wires across the top of the fender to the bulkhead passthrough at the firewall. I reused this from the 4cyl, but they WERE NOT the same from 98 to 99. They were very similar, but they were not the same. I had to reroute the starter command wire, I had to add a wire from the underhood fuse panel to the engine connectors at the firewall/valve cover, and I had to jumper a wire from one of the valve cover plugs to a pin on the other plug. The only way I figured all this out was by going through the pinouts on the valve cover connectors (there are two, 103 and 104, I think they're named) and checking each circuit from the 98 to 99 to make sure they were the same.

I have the FSM wiring diagrams for 97 and 98 if you need them. Send me a PM, and I can figure out how to get them to you.

HTH
 
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I went 97 into a 97 and did all the fabing of engine mounts and just reworked everything else. I didn't have half of the problems Shawn listed.

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We are very lucky I guess, because EVERYTHING mated up just fine, mechanically. The only issue we are having is the wiring harnesses.... last item on the list.
 
Im finishing mine up as we speak also. My plugs didnt match. The jeep had a square grey plug, as my harness had a rectangle black plug. I had to figure each wire to get it running.
 
Oh, and in case anybody's wondering, it took a solid three weekends to make this happen.

First w/e: Pull donor motor. Pull it apart, replace gaskets, clutch, etc. Cut off motor mounts (reciprocating saw w/8-12" blade worked well)
Second w/e (snip from an email I sent to a friend):

Last weekend, I cut the motor mounts out of the blue Jeep. While I was doing that, I realized that the fenders were completely in the way, and would be in the way when it came time to weld the motor mounts into the red Jeep. I also finished going through the new motor, installed the flywheel and clutch, and reattached the transmission. I also started tearing down the red Jeep, mostly underneath -- disconnecting driveshafts & wiring, draining fluids, etc. One night last week, I pulled the whole front clip off of the red Jeep. It wasn't terrible... mostly just a bunch of bolts (air ratchet was exceptionally helpful here). As of Friday night, the only thing left on the 4cyl was to drain the power steering fluid and unbolt the motor mounts.

Saturday, it rained all day. I put out the EZ Up and still managed to get some stuff done, but it mostly sucked. I got the 4cyl pulled, cut the 4cyl motor mounts off, and swapped the input shafts on the transfer case.

The plan Sunday morning was to swing the 6cyl in place and weld in the motor mounts. I figured that if I had them bolted to the motor, they'd sort of self-locate on the frame. That didn't exactly work out. I used the transmission mount to hold the trans centered and located fore/aft, but the engine was still swinging in the air, and didn't really want to settle down hard on the frame. So I took careful measurements off the old chassis, unbolted the motor mounts from the motor, and tacked them to the frame where I thought they were supposed to go. I set the motor down on them, everything looked good, so I burned them in. Setting the motor down that last time was pretty awesome.

I spent the rest of the day reinstalling stuff and hooking things up. As it turns out, the chassis side harness is NOT the same from 98 to 99. The plugs where the engine harness attaches are different, and it looks like they have different wire counts/colors. I'm going to have to look into that a bit more. I've got to figure out what to do about the exhaust, fill everything with fluid, reinstall the fenders, driveshafts, and a bunch of other odds and ends.

Third weekend: Build exhaust (helps if you have the downpipe from the 6cyl exhaust manifold to the cat!), install transfer case, driveshafts, install front clip, fill with fluids, modify wiring harness, reinstall transmission shifter & interior trim, adjust transfer case linkage, etc.

I fired it for the first time on Saturday afternoon, but it didn't move for the first time until Monday afternoon. The little stuff sucks up a LOT of time. I spent a LOT of time looking around for miscellaneous fasteners, etc... and I felt like I'd been pretty good about bagging things up in sandwich bags as it came apart.
 
I'm not saying its easy (or tooting my horn) but I did mine in a weekend, had to have it driving for work Monday. Other little stuff was finished up later, (front DS, tail pipe)

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Damn, Sounds like I had the perfect situation.

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I'll get you the wiring diagrams tonight. The plugs come apart pretty easily. So long as you have enough pins, you can probably remove the plug from the donor motor and put all its wires into the plug from the dead 2.5L. Then, the only question is what is missing from the 2.5L chassis harness.
 
Help please !!

I just swap a 2001 tj 4.0l into a 1997 tj 4cyl....change all the wiring harness and pcm even the complete dash still wont start just crank....as I am reading I see that I might have to cgange the steering colum for the key ???..the one I have from the 01 the ignition switch is bad is it gonna work if I change the switch ??? Thanks any help is appreciated
 
jeeper200137irok said:
Help please !!

I just swap a 2001 tj 4.0l into a 1997 tj 4cyl....change all the wiring harness and pcm even the complete dash still wont start just crank....as I am reading I see that I might have to cgange the steering colum for the key ???..the one I have from the 01 the ignition switch is bad is it gonna work if I change the switch ??? Thanks any help is appreciated
Click to expand...

If the 01 has the "smart" keys, you will need the smart key and the sensor from the 01 (top, center of the steering column near the cylinder). If the key doesn't match, there should be a light on the dash that lights up. IIRC, it's yellow, has a picture of a key with a circle and line through it. If the key doesn't match the one programmed into the ECM, the light comes on. Starter spins, but motor does not fire.

You could sit the "old" key next to the sensor, zip tie it in an out-of-the-way place, then use the cylinder and key from the 97. That would effectively disable the sensor, since it would always have the correct key nearby.
 
Cool I will try that... the key from the 2001 just look like a normal key maybe thd chip is hidden inside...I also have another 2001 junk ...if I take the steering colum in that one I wonder if it would work or I have to take that pcm too
 
jeeper200137irok said:
Cool I will try that... the key from the 2001 just look like a normal key maybe thd chip is hidden inside...I also have another 2001 junk ...if I take the steering colum in that one I wonder if it would work or I have to take that pcm too
Click to expand...

The "smart" keys have a big, fat, rubber end on them. The chip is inside.

As I recall, you need the matching PCM, key, and sensor from the same vehicle.
 
Falko said:
Unless the TJ SKIM system is different than the WJ, it should fire up and run for about 2 seconds with a mismatched key.
Click to expand...

It will until it sees an unrecognized key attempt 5 times IIRC. Then it goes into a lock out mode.

@jeeper200137irok, does the 01 TJ have a grey colored key? If so it has SKIM and you'll need the column from that Jeep.
But first, see what's missing. Spark, fuel pressure and/or fuel injector pulse. That'll tell you where to start. Do the gauges move when you turn the key on?
 
Thanks guys , it has a black key ...I ended up changing the wiring harness inside the jeep...not the one in the dash wich I already change but the one with the fuse box and all that shit and it fired right away....must be different where all yhe plugins are ...well at least I got that part figure out !
 
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