1998 TJ 4.0L into a 1995 2.5L ??? - JeepForum.com
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Unread 01-30-2014, 05:44 AM   #1
StanF
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1995 YJ Wrangler 
 
Join Date: Feb 2013
Location: Austin, Texas
Posts: 1,045
1998 TJ 4.0L into a 1995 2.5L ???

I'm planning on doing a 4.0L swap in 2-3 months, and I'm on the hunt for a good used engine. My best option so far is a 1998 TJ motor with just under 100k miles. I'm ready to pull the trigger on it, but wanted to confirm a couple of things with the experts. I'm keeping everything stock 1995 OBD1.

I think I can just use the engine as is. The flywheel is the same, so not problem with the CPS. I might need to swap over a sensor or two, since my 1995 is OBD1, and the 1998 is OBD2. Worst case, maybe I swap out the intake manifold, but this seems unnecessary from what I've read. Is this correct? Am I missing anything???


As a side note, a few months ago I got a complete 1995 4.0L that I can use for parts. Its rings are pretty worn, which is why I'm not using it for the swap. I didn't pay much for it.

To help keep things on track:
0) yes, I want a 4.0L
1) no, I can't afford a stroker right now, unfortunately
2) no, I don't want to keep the 2.5L - it doesn't work for me. That's great if it does everything that you need!
3) no, I don't want to do an SBC, 4.3L V6, Ford 302, or 4BT. All very, very interesting, but that's not where I'm going right now.


BTW, buying a used motor is definitely "Buyer Beware"...I'll add a funny (sad?) story about trying to buy a 4.0L engine from a relatively local used Jeep parts dealer. I talked to him for a couple of weeks via email about a 1994 YJ engine with 110K miles. He sent me a picture of the engine in the Jeep - it was an automatic Jeep, as you could see the transmission dip stick. He said it was a complete engine except for the AC compressor.

He brings it to me on Saturday. First, everything except the timing chain cover was stripped off the front of the motor. The exhaust manifold was cracked. The fuel rail was removed. I did a leak down test on it, and it was pretty bad. Every sensor was broken - oil pressure, temperature, etc. Basically, it was a worn out boat anchor. And it wasn't the engine that was in the picture. The one he brought was out of a manual transmission Jeep, as it still had the clutch and pressure plate installed.

He was either trying to scam me or was just a disorganized mess and didn't know what he was selling. In either case, I won't be giving him any business. And no, I didn't keep the engine!

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Unread 01-30-2014, 06:36 AM   #2
Que89YJ
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1989 YJ Wrangler 
 
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No guage temp sensor in the rear of the head. Fuel rail is different. Distributor is different. You will need the electronics from a 4.0L to make it work. You will need to add 2 injector wires to the 2.5L harness and a 4.0L ecu.
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Unread 01-30-2014, 07:24 AM   #3
StanF
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Quote:
Originally Posted by Que89YJ View Post
No guage temp sensor in the rear of the head. Fuel rail is different. Distributor is different. You will need the electronics from a 4.0L to make it work. You will need to add 2 injector wires to the 2.5L harness and a 4.0L ecu.
Great comments - thanks!

More detail please!:
"No guage temp sensor in the rear of the head."
What's the recommended solution for this?

"You will need the electronics from a 4.0L to make it work. "
Can you give more detail what you mean? Or are you just thinking of the ECU?


Should be no problem:
(It sounds like the donor 4.0L will come in handy!)
"Fuel rail is different."
No problem - I have one from my other 4.0L.

"Distributor is different."
No problem - I have one from my other 4.0L, if I need to swap it out.

"You will need to add 2 injector wires to the 2.5L harness and a 4.0L ecu."
Yes, I've already got a spare wiring harness for the extra injector wires and 4.0L ECU.
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Unread 01-30-2014, 08:18 AM   #4
Que89YJ
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1989 YJ Wrangler 
 
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Ecu was what I was refrencing. The temp sensor can be relocated to another port on the block. There are a few but they dont go into the coolant or drill and tap the tstat housing.
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Unread 01-30-2014, 08:54 AM   #5
StanF
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1995 YJ Wrangler 
 
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Location: Austin, Texas
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Quote:
Originally Posted by Que89YJ View Post
Ecu was what I was refrencing. The temp sensor can be relocated to another port on the block. There are a few but they dont go into the coolant or drill and tap the tstat housing.
Thanks again!

No problem on the temperature sensor - I can get that figured out pretty easily. Basically, the '98 4.0L won't be a drop-in replacement, but none of the little issues scare me.

I found this thread - it also had some good info:
http://bb.bc4x4.com/showthread.php?1...nto-94-XJ-OBD1

Here's the best info from that thread:
HOW TO SWAP A 1999 TJ 4.0 OBD2 ENGINE INTO A 1994 XJ 4.0 OBD1 JEEP

This is an easy way to swap old for new style engines. We used the newer intake manifold with old fuel rail and the original wiring harness and sensors.

Our donor engine came as a standard, complete with alternator, steering pump, starter, clutch pressure plate distributor everything. Thanx Dan.

All the electrical components will be swapped from the OBD1 onto the OBD2 engine. The electrical connectors are different. This will include all sensors, fuel rail injectors, and throttle body.

We were swapping a standard into an automatic. So we had to remove the clutch & pressure plate and re use the flex plate, torque converter and crankshaft position sensor along with engine mounts.

There are components you must retain from the 1994 XJ OBD1 engine.
This is mainly due to the electrical connections on the main wiring harness.

-fuel rail and injectors: has OBD1 style electrical connections and fuel line connections
-throttle body with sensors attached
-throttle cable bracket: to fit existing cables
-intake manifold air temperature sensor: relocate on OBD2 manifold extend wires 6”
-oil sender
-oxygen sensor
-water temp sender: relocated to side of block with pipe thread adapter and longer wire
-distributor camshaft position sensor: retain OBD2 distributor, swap out CPS to OBD1 (two screws).
-t-fittings to vacuum lines some rearranging of lines was necessary, but that will be obvious.
-fuel line bracket drill hole and fasten to new style manifold

There are some mechanical components to swap.

-the water pump must be swapped from the OBD1 onto the OBD2 engine:the XJ fan does not run off the water pump as does the TJ setup. Retain the pulley from the OBD1 pump.
.-use OBD2 power steering pump. This bolts to new style manifold. It has an extra idler pulley with the assembly for belt tension adjustments. Use OBD2 belt arrangement
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