97-99 Engine into my 91 Comanche

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Hey everyone, I have recently swapped a 99 XJ 4.0L into my 91 MJ and because of all the confusion I found researching the topic, I decided to create a solid write up on this. My 99 engine still contains the new style intake manifold to maintain the better air flow. This will be mostly text here, but I have created a video for YouTube to show that this DOES in fact work like stock (link at the bottom for those that don't want to read all this).

 

The first thing I'll say is this: the golden rule to the 4.0 swaps are that newer engines generally work perfect in the old style, but NOT the other way around! And the reason I say generally is because I cannot say every swap will be guaranteed to work. However, for the sake of this write up, I WILL ONLY BE DISCUSSING XJ TO XJ/MJ SWAPS.

 

I recommend you do not throw ANYTHING away until the swap is completed. Having all the parts around may be a little cluttered, but you'll be very happy when you have the old parts to reference. Even better, I was able to keep the entire wrecked 99 XJ nearby through the whole process.

 

 

DOING THE SWAP

First off, the swap itself. If you are reading this, I assume you have the skills/confidence/knowledge to unbolt an engine, pull it out, and put another nearly identical engine in its place. This is about as bolt in as a swap like this could be.

 

ELECTRONICS

Just about every single plug/sensor there is in the 97-99 engine is DIFFERENT from the pre-97 engines, even though the sensor works almost the exact same. Here's a list of the sensors/electronics you need to KEEP FROM THE OLD STYLE ENGINE:

-Oil pressure sensor

-Coolant temperature sensor

-Coil pack

-Distributor

-Idle air controller

-Throttle position sensor

-Intake temperature sensor

-O2 sensors

-Injectors

-Crank position sensor

-Alternator

-Cruise control actuator

 

There may be some I'm forgetting (as my MJ is a base model), but if it has a plug, keep the old style. Some things you do not need to swap over, like the starter, battery cables, etc. as they are nearly identical. As for the AC system, I do not know for sure, as my MJ came factory with no AC, but I imagine the plugs will be different and you may need an old style AC system.

 

 

NON ELECTRICAL SYSTEMS

There are some things when keeping the new style intake manifold you will need to keep from the old style, but some things it is often better to have the new style. Here are things you should consider with the year model listed beside it:

-99 Power steering pump (the old style bolts on different)

-99 Heater core hoses (I highly recommend a heater control valve delete)

-91 Throttle body (to accommodate the old style sensors mentioned above)

-91 Exhaust (to maintain proper O2 sensor locations)

-99 Intake (of course)

-99 AND 91 Vacuum lines & connectors (See below)

-99 Vacuum canister (the smaller size is just nice to have with aftermarket bumpers, but not necessary)

-99 Fan shroud (not required but nice to have the correct belt diagram)

-91 Fuel system (rail, lines, regulator, etc)

 

Most of the rest of these things are pretty self-explanatory as they are identical year to year, such as the air box and intake elbow and radiator, or because they came with the package, such as valve covers, anything else pulley driven, etc.

 

 

VACUUM LINES

It is important that you take as many vacuum lines as you can, but crucial that you have the vacuum line FROM THE ENGINE ALL THE WAY TO THE CANISTER. This line is easy to remove as it is very flexible. Take all the elbows, connectors, everything. Using the extra vacuum lines, it is possible to connect all the required items to the vacuum system, such as the brake booster, breathers, MAP sensor, intake temp sensor, fuel pressure regulator. Everything that was once connected to the old intake manifold should STILL BE CONNECTED TO THE NEW INTAKE MANIFOLD. Special pieces you may not think to grab are the small canister, as many elbows and plugs as you can carry (since you may come across rotten ones), and the T fitting threaded into the manifold near the power steering pump.

 

 

MISC. ADVICE

Here's what I'd do when doing the swap if I were to do it over again with my current knowledge:

-New CPS while the engine is out (it bolts to the bell housing)

-Replace the alternator while the engine is out

-Do a complete maintenance checklist since you have to replace all the fluids anyways (for example, might as well get a new air filter and spark plugs too)

-Address any known oil leaks (seals are cheap and no better time to do it)

-Flush out the heater core (you may be surprised how dirty it is)

-Clean and coat your floor pans if they haven't started to rust (northern states)

-Check the condition of your brake lines with the engine out of the way

 

 

MANUAL TRANSMISSION SPECIFIC

If you have the AX-15 in your MJ, MEASURE YOUR PILOT TIP. if it is NOT a 3/4" tip, you will need a custom pilot bearing. THERE ARE NO AUTO PARTS STORE THAT OFFER THIS ON THE SHELF. I checked AutoZone, O'Reilly, Advanced Auto, Napa, Pep Boys, KOI, and even called around a few small time local stores. I ordered the adapter pilot BUSHING from Novak. This isn't a plug for them, just a product I found that works. MAKE SURE YOU GREASE THE BUSHING LIKE YOU WOULD IN ANY BUSHING STYLE ENGINE. Here are the sizes:

 

-Pilot Tip:

--88 to early 92 19/32" Diameter

--Late 92+ 3/4" Diameter

 

-4.0L Crank Bore:

--Pre 92 1-1/16" Crank

--92+ 1" Crank

 

You cannot make the mistake of running without one of these on your manual transmission. It will create a ton of premature wear and ruin the transmission. You must also be careful to notice that if the engine is pulled from an automatic, it will NOT have a pilot bearing, as the torque converter doesn't require one.

 

This is about all the information I can think up right now. If you have any questions or think I made a mistake let me know and I will explain how I came to each conclusion above. PLEASE REMEMBER, THIS IS FOR CHEROKEE AND COMANCHE ENGINES ONLY. I AM NOT DISCUSSING BRINGING IN ENGINES FROM WRANGLERS OR GRAND CHEROKEES. I’m sure that you can but be careful that you ONLY use engines with distributor systems. NOT COIL PACKS.

 

Lastly, I have made a YouTube video pointing out and showing many things I have discussed here, but more importantly, visuals of everything and proof that it works like it would from the factory. Here’s the link: