Swapping a 99 XJ motor into a 87 MJ. (both are 4.0 liters)

[KANTANKRUS]

What will I need? The XJ motor will be gone through, before the swap. Power enhancements may be included, but not 100% necessary, as I want reliability over increased HP.

 

Please advise.

[Pete M]

the link in my signature should have some info on swapping blocks around.    might be down in the conversions section.

[cruiser54]

Here ya go. 

 

CRUISER'S MOSTLY RENIX TIPS

HO INTO RENIX SWAP

OCTOBER 31, 2015 SALAD 76 COMMENTS

 

This swap is easier than some will lead you to believe. And generally Pooh-poohed by those who have never done it. Those of us who have done it, like myself, will share with you the things that need to be done for a successful swap. Just think of it as swapping in a long block.

• XJ Cherokee and ZJ Grand Cherokee 4.0L engine blocks interchange.
• 2000+ TJ Wrangler and WJ Grand Cherokee 4.0L engine blocks interchange.
• YJ and 1997-1999 4.0L TJ blocks will interchange in XJ/ZJ
• XJ/ZJ blocks, and the 2000+ TJ/WJ blocks do not interchange without significant modifications.

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.

Now that we know which engines we can use, let’s get down to business.

The HO and Renix have some differences but none that can’t be overcome very easily.

One running change was that the rear of the head was no longer drilled and tapped for the temperature gauge sender beginning in the 96 model year. The sender can be relocated to the threaded hole in the thermostat housing taken from an HO engine. You’ll have to extend the wire to that location. Some brave souls even drill and tap the HO head at the rear for the sender.

You will be using the intake and exhaust manifolds from your Renix, along with all your sensors and wiring. Since the intake ports of the HO are slightly different, you use a new Renix gasket. Exhaust ports are identical.

An alternative on exhaust manifolds:

As far as exhaust, you can use the Renix exhaust manifold and be fine.
If you want to use the HO exhaust manifold, you must go with an HO headpipe and screw your O2 sensor into that headpipe. Standard Renix harness is plenty long to do so.
A bung can be welded into the HO manifold to accept the EGR tube.

You will need to use your Renix distributor as it is different than the HO design. See Tips #12 – Setting Your 4.0 to #1 TDC and #13 – Distributor Indexing to be sure you get the distributor installed correctly.

The flywheel or flexplate from the Renix must be used so your CPS gets the correct signals. The valve cover from the Renix allows you to keep your CCV system intact and requires no modifications.

The HO block will have a plug in the coolant galley on the driver’s side of the block, closest to the front, which needs to be removed so your Coolant Temp Sensor can be installed in it’s place just as it is on the Renix. It requires a 5/16” square drive or a modified 3/8” drive that has been ground down to fit. Do this before installing the engine.

As for the knock sensor, which is located just above the oil pan on the driver’s side of the engine about mid way, all the blocks I’ve seen are threaded for it. If not, I’ve heard they may be drilled but not tapped. Tap the hole if that’s the case.

 

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)

[KANTANKRUS]

I guess, my biggest concern lies in the PCM of the 87 MJ, verses the 84 to 01 XJ Cherokee (not Grand). Will the 87 MJ PCM interchange with the newer XJ engine? Furthermore, I would like to upgrade to OBD verses the Renix controlled engine, or is this even possible without a major domino effect?

I would like to Nix the Renix!

 

[KANTANKRUS]

I suppose I know that answer! The only way to 'Nix the Renix' is to gut the truck and install a whole XJ PCM system, including but not limited to, dashboard, steering wheel/column and firewall enhancements... jeesh!

 

And if I have to do that, then a V8 is going into it.

[Pete M]

The only way to get an OBD is a wholesale swap. But this can be from a 91-95 so you can keep the old dash. 96 will give obd2. Still a bunch of work but it all bolts in and only costs as much as a used xj. 

Or just keep the renix and tackle all of cruiser's renix tips. There's nothing inherently wrong with the renix fuel injection.  and with the aftermarket dash plugin (whose name escapes me) you can get real-time data on all the sensors.

[cruiser54]

Just put the engine in as outlined. Nothing wrong with Renix. Its ECU will work just fine. If you want some more power, swap in a 1990 Renix ECU. 

[Pete M]

this li'l guy.  you'll have real-time info about how things are going.  

 

https://nickintimedesign.com/product/renix-engine-monitor-ii/

[KANTANKRUS]

12 hours ago, Pete M said:

The only way to get an OBD is a wholesale swap. But this can be from a 91-95 so you can keep the old dash. 96 will give obd2. Still a bunch of work but it all bolts in and only costs as much as a used xj. 

Or just keep the renix and tackle all of cruiser's renix tips. There's nothing inherently wrong with the renix fuel injection.  and with the aftermarket dash plugin (whose name escapes me) you can get real-time data on all the sensors.

Pete,

After much thought, I may just keep it stock with its current engine... not many miles on it really, if I remember correctly near 130k. But my main concerns have always been reliability and the header, I have read that it is prone to cracking. And now I see that the rear main seal is leaking.

 

Cruiser's tips might become a way to rewire my BRAIN and just learn my way through all of this older technology.

[cruiser54]

Oh, okay. 130,000 miles? That's nothing. 

They all had header cracking issues. Not just Renix. LOL

 

Sure it's your rear main seal? 

 

I bet it's not!!  See below. 

 

CRUISER'S MOSTLY RENIX TIPS

REAR MAIN SEAL DIAGNOSIS

OCTOBER 31, 2015 SALAD 3 COMMENTS

 

I’d be looking up ABOVE first, and VERIFYING the source of the oil leak YOURSELF.

Everybody, who doesn’t own or have to pay for or perform your vehicle repairs, loves to poke their noggin UNDER the Jeep and come out bearing the false bad news that your RMS is leaking. Many mechanics, friends, and good old Uncle Bob seem to enjoy telling you it’s the rear main seal. Has a catastrophic ring to it, doesn’t it?

A simple leak at the back of the valve cover or other source could produce the same symptoms. You don’t need to be a mechanic to figure this out. If you have good eyesight and a dim flashlight, you’re good to go on your own. Don’t jump on the RMS/oil pan gasket bandwagon right off the bat.

Almost any oil leak on your 4.0 is gonna drip from the RMS area for two simple reasons:

First off, the engine sits nose-up and any oil will run back to the RMS area.

Secondly, the RMS area is also the lowest point on the engine. Simple physics and the old plumber’s adage apply here: “Crap flows downhill”.

Valve cover gasket, oil pressure sending unit, oil filter adapter seals and distributor gasket, in that order, have to be eliminated as possibilities first.  A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly. 

 

 

[KANTANKRUS]

3 hours ago, cruiser54 said:

Oh, okay. 130,000 miles? That's nothing. 

They all had header cracking issues. Not just Renix. LOL

 

Sure it's your rear main seal? 

 

I bet it's not!!  See below. 

 

CRUISER'S MOSTLY RENIX TIPS

REAR MAIN SEAL DIAGNOSIS

OCTOBER 31, 2015 SALAD 3 COMMENTS

 

I’d be looking up ABOVE first, and VERIFYING the source of the oil leak YOURSELF.

Everybody, who doesn’t own or have to pay for or perform your vehicle repairs, loves to poke their noggin UNDER the Jeep and come out bearing the false bad news that your RMS is leaking. Many mechanics, friends, and good old Uncle Bob seem to enjoy telling you it’s the rear main seal. Has a catastrophic ring to it, doesn’t it?

A simple leak at the back of the valve cover or other source could produce the same symptoms. You don’t need to be a mechanic to figure this out. If you have good eyesight and a dim flashlight, you’re good to go on your own. Don’t jump on the RMS/oil pan gasket bandwagon right off the bat.

Almost any oil leak on your 4.0 is gonna drip from the RMS area for two simple reasons:

First off, the engine sits nose-up and any oil will run back to the RMS area.

Secondly, the RMS area is also the lowest point on the engine. Simple physics and the old plumber’s adage apply here: “Crap flows downhill”.

Valve cover gasket, oil pressure sending unit, oil filter adapter seals and distributor gasket, in that order, have to be eliminated as possibilities first.  A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly. 

 

 

Sure will, check em out... but not until after mid June 2023, that is when I will finally be seeing 20/20 again. Cataract surgery, on these eyes!