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Questions about swapping different year/model 4.0s

So if I understand this correctly, pretty big "if", I should hold onto the head and exhaust manifold for my '95 4.0 as they *should* bolt on to my '99 block.

By doing so I *should* be able to see some modest performance gains on the '99 due to the more freely flowing head and exhaust ports of the earlier version.

Assuming that I am correct so far in my thinking, can anyone forsee any complications from the OBDII system as a result of the head swap?
I'm reasonably certain you can just run a whole '99 longblock in a '95 without issues. The one thing you'll need to do is drill and tap a 1/8"-27 NPT pipe thread into a boss on the thermostat housing and extend one wire for your temp gauge sending unit, which is a 15 minute project including scraping the gaskets off and installing a new one.

In fact I have a 98 ZJ longblock in my 91 MJ right now.
 
I'm reasonably certain you can just run a whole '99 longblock in a '95 without issues. The one thing you'll need to do is drill and tap a 1/8"-27 NPT pipe thread into a boss on the thermostat housing and extend one wire for your temp gauge sending unit, which is a 15 minute project including scraping the gaskets off and installing a new one.

In fact I have a 98 ZJ longblock in my 91 MJ right now.

You absolutely can do this swap.

If you use the thermostat housing from the 98, it's already tapped.
 
Not quite - the thermostat housing only has one tapped opening in it, for the HO ECU's temp sender. It's a larger size, iirc 3/8 NPT. You have to drill and tap a *second* hole for the 1/8 NPT gauge sender, which is located in the driver rear corner of the head on 87-96 4.0s.

I believe you are correct for putting a 97+ HO longblock into a RENIX - since the ECU temp sender is on the lower driver side of the block on those, you can just use the HO thermostat housing and a threaded adapter to put the temp gauge sender into the spot where the HO ECU's temp sender would normally go.
 
Not quite - the thermostat housing only has one tapped opening in it, for the HO ECU's temp sender. It's a larger size, iirc 3/8 NPT. You have to drill and tap a *second* hole for the 1/8 NPT gauge sender, which is located in the driver rear corner of the head on 87-96 4.0s.

I believe you are correct for putting a 97+ HO longblock into a RENIX - since the ECU temp sender is on the lower driver side of the block on those, you can just use the HO thermostat housing and a threaded adapter to put the temp gauge sender into the spot where the HO ECU's temp sender would normally go.

Hey. I'm a Renix guy. What can I say? Thanks for the clarification.
 
I figured - at first I was like "wait, what?" and then realized you were likely speaking from a RENIX viewpoint.
 
I'm reasonably certain you can just run a whole '99 longblock in a '95 without issues. The one thing you'll need to do is drill and tap a 1/8"-27 NPT pipe thread into a boss on the thermostat housing and extend one wire for your temp gauge sending unit, which is a 15 minute project including scraping the gaskets off and installing a new one.

In fact I have a 98 ZJ longblock in my 91 MJ right now.

I'm actually going the other way...sort of. The '95 is the donor and the '99 is the driver. no issues with the '99 engine at all. It was just my understanding that the later heads are more restrictive due to changes in emissions control requirements; hence the revised intake manifolds which have become a popular swap on pre-99 engines.

As such, I was thinking that if i were to swap a pre-99 head onto a post-99 motor there, in theory, should be some gains from the swap. Gains similar to those seen when swapping post-99 intakes onto pre-99 engines. No?
 
What head does your 99 have? AFAIK they all got basically the same head as earlier ones, but some have said they got 0331s in later months. Then again I don't know if the 91-9? vs 9?-99 non-0331 head flow differently, I haven't really looked into that.

As for intakes, the 99+ intake manifold does provide some benefits supposedly, especially when combined with other mods like a freer exhaust and/or stroking/forced induction etc. You can simply bolt those onto earlier engines (at least as early as 91) though, no need to change heads.

I have the motor out of a 94 in my 98, so yeah, you can do that swap no problem too. Ended up doing that because it was the first one that came along when I needed one and I got a good price on it. The only thing I had to do was trim the timing indicator boss off of the timing cover because the later belt routing interfered with it, oh, and I had to put a 1/8 NPT plug in the cylinder head where the temp gauge sender would have gone... so yeah, I guess I have a 98 motor in my 91 and a 94 motor in my 98. If things had gone differently, I probably would have ended up with a 98 motor in the 98 and a 94 in the 91, but that's not how things ended up.
 
So if I understand this correctly, pretty big "if", I should hold onto the head and exhaust manifold for my '95 4.0 as they *should* bolt on to my '99 block.

By doing so I *should* be able to see some modest performance gains on the '99 due to the more freely flowing head and exhaust ports of the earlier version.

Assuming that I am correct so far in my thinking, can anyone forsee any complications from the OBDII system as a result of the head swap?

All 1975-up AMC six heads swap freely between blocks - they went to a "wide deck" block for '75. So, the top end will swap freely between all 6-242 engines, just know that the RENIX head (#2686) won't swap intakes with the later heads. Also, know that the 6-258 manifolds won't swap onto 6-242 heads - the intake ports are in the wrong places, and the #3 & #4 exhaust ports are Siamesed.

If OBD-II doesn't like your OBD-I throttle body setup, just swap the throttle bodies - 1991-2006 TB assemblies, as I recall, use the same mounting stud pattern.
 
New to forum but not new to Jeeps. Just looking for some confirmation on my jeep before i order the parts. I have a 2000 XJ sport i just bought. Very Clean with 115k miles on it. The motor has a hole in the #2 piston and the head has 2 small cracks in it. I have a 94 xj 4.0 that i recently swapped out do to oil consumption, motor was running fine just burning oil. I tore down motor and its in great shape minus the rings. My plan is to freshen up the bottom end and purchase a reman head for a 2000 and put it on the rebuilt 94 short block. just trying to clarify that this will work before i commit to buying the parts. i know about having to swap over the cam sensor into the dizzy hole but just making sure everything else is a go. i have both oil filter adapters so i have that covered as well. thanks for the advice in advance.
 
All 1975-up AMC six heads swap freely between blocks - they went to a "wide deck" block for '75. So, the top end will swap freely between all 6-242 engines, just know that the RENIX head (#2686) won't swap intakes with the later heads. Also, know that the 6-258 manifolds won't swap onto 6-242 heads - the intake ports are in the wrong places, and the #3 & #4 exhaust ports are Siamesed.

If OBD-II doesn't like your OBD-I throttle body setup, just swap the throttle bodies - 1991-2006 TB assemblies, as I recall, use the same mounting stud pattern.

Actually, you can swap intakes and heads between Renix and early HO. 1/4" difference in intake port size. If you're up to it. the head and intake can be port matched quite easily.
 
New to forum but not new to Jeeps. Just looking for some confirmation on my jeep before i order the parts. I have a 2000 XJ sport i just bought. Very Clean with 115k miles on it. The motor has a hole in the #2 piston and the head has 2 small cracks in it. I have a 94 xj 4.0 that i recently swapped out do to oil consumption, motor was running fine just burning oil. I tore down motor and its in great shape minus the rings. My plan is to freshen up the bottom end and purchase a reman head for a 2000 and put it on the rebuilt 94 short block. just trying to clarify that this will work before i commit to buying the parts. i know about having to swap over the cam sensor into the dizzy hole but just making sure everything else is a go. i have both oil filter adapters so i have that covered as well. thanks for the advice in advance.
You'll be fine, make sure to cut the timing indicator thing off the timing cover (it's right near the timing indicator marks... weird round thing with a hole in it. just cut it off) so that the serpentine belt doesn't hit it.
 
Hey guys, bringing this old thread back to life since I have some questions that seem like you guys know the answers to.
I have a 2002 TJ 4.0, #4 piston blew on the highway, rod and pin still attached so it killed the bore. I also have a '98 Grand Cherokee with a good 4.0, complete. So my plan was to swap the GC engine into the TJ and use the TJ head but hearing it may not work or will need a ton of fab work to use it.
A used TJ engine here is $750 for something local, or I can spend half that but drive 4 hours each way to get it, so.....trying to use what I already have if possible.
Any help would be greatly appreciated. I only found this site as a fellow Jeep brother linked it in a local Jeep forum where I was asking the same question.
 
XJ Cherokee and ZJ Grand Cherokee 4.0L engine blocks interchange.

2000+ TJ Wrangler and WJ Grand Cherokee 4.0L engine blocks interchange.

XJ/ZJ blocks and 2000+ TJ/WJ blocks do not interchange without significant modifications. (1991 to 1995 YJ and 1997-1999 4.0L TJ Wrangler blocks will interchange in XJ/ZJ and visa-versa).

TJ/WJ 4.0L Engine blocks underwent clean sheet design changes effective in the 1999 WJ Grand and 2000 TJ Wrangler. These blocks are not interchangeable with XJ/ZJ engine blocks. The reason is motor mount bolt holes and belt driven accessory mounting bolt holes are in different locations, or not present at all, TJ/WJ vs. XJ/ZJ.


XJ: "Regular" (not Grand) Cherokees 84-01
ZJ: Grand Cherokee 93-98 (Gen1)
WJ: Grand Cherokee 99-04 (Gen2)
YJ: Wrangler 87-95 (Gen1)
TJ: Wrangler 97-06 (Gen2)
 
Thanks for the quick reply.
So this will not work?
I'm sure I can make new motor mounts or adaptor plates, but with regard to the accessories, can I just use the GC stuff?
 
TJ/WJ 4.0L Engine blocks underwent clean sheet design changes effective in the 1999 WJ Grand and 2000 TJ Wrangler. These blocks are not interchangeable with XJ/ZJ engine blocks. The reason is motor mount bolt holes and belt driven accessory mounting bolt holes are in different locations, or not present at all, TJ/WJ vs. XJ/ZJ.
 
What he is saying is no.

However, a 99-04/05 (I forget when wj production stopped) wj block will fit great. Aim for one with the tupy 0331 head already on it, should be late 02 or so or all 03s and later but verify before buying.
 
Thanks. My problem is I already own the GC so its a free engine aside from labour. I understand they underwent changes, but motor mounts can be made/swapped without much work, and if the front acc. drive has different mounting, would it not be possible to run the complete GC engine with acc. still on it and just use/modify my TJ lines to fit?
I know they are "not interchangeable", but can will they work, and if so with what changes?
 
When he says not worth it he means it, the AC compressor is on the other side under the manifolds, etc etc. Feel free to try it, but there's a reason no one does it.

WJs on the other hand are probably pretty plentiful.
 
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