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Discussion Starter · #1 ·
In the process of swapping a 1999 TJ 4.0L OBD2 engine into a 1994 XJ 4.0L HO. With this swap we are retaining the XJ wiring harness. It appears the OBD2 engine has no temperature sending unit. Can't see one anywhere. From the factory the head has not been drilled and tapped at the rear of the engine to receive the sender as with the OBD1 motor. Who knows anything differant?
 

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Thats right the newer motor does not have the temperature sending unit hole at the back of the head.

That is just the guage sending unit though, the computer doesnt use it, the computer uses the sensors on the thermostat housing.

I always used an aftermarket guage in my XJ so I didn't worry about it. If you want to retain the stock sending unit there is a pipe plug that uses a 5/16" square on the block behind the motor mount that goes into the water gallery that I always used for my mechanical guage. You'll just need to bushing it to the right size and extend the wiring to reach

Dan.
 

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id say use the 94 head if you can. in 99 the ports are smaller for emissions. or just port the 99 head..
 

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Discussion Starter · #4 ·
Thats right the newer motor does not have the temperature sending unit hole at the back of the head.

That is just the guage sending unit though, the computer doesnt use it, the computer uses the sensors on the thermostat housing.

I always used an aftermarket guage in my XJ so I didn't worry about it. If you want to retain the stock sending unit there is a pipe plug that uses a 5/16" square on the block behind the motor mount that goes into the water gallery that I always used for my mechanical guage. You'll just need to bushing it to the right size and extend the wiring to reach

Dan.
Could also "T" in @ the thermostat housing.
 

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Discussion Starter · #6 ·
Does the computer compensate for slightly larger or slightly smaller injectors by modifying the pulse rate to the injectors?
 

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it shouldn't care too much, it will read the oxygen sensor as rich and then compensate right?

I ran mustang injectors on my XJ, not for more performance, just because the originals were leaking and I had a bunch of spare mustang injectors, it always passed aircare.
 

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Discussion Starter · #8 ·
Finally got the engine installed with a few mods. Very easy conversion.Runs really smooth.Thanx for the solid engine Dan.
 

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Care to explain the mods you made to get everything running? It'd be a nice way to finish the thread, and give me more to think about.
 

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Doug it's pudge, come look at mine, I have mine all hooked up stock like, you will need a new dash, I have that too if you haven't already got it. Only thing I haven't got hooked up is a tach? I could use some help with that. I have the wires there for auto fan on/off too so you can trace the routing.
 

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Discussion Starter · #12 ·
Care to explain the mods you made to get everything running? It'd be a nice way to finish the thread, and give me more to think about.
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


Some helpful 4.0L engine swap sites:

http://www.go.jeep-xj.info/HowtoIntakeManifold1.htm
http://wilhelm-tech.com/jeep/mods/40EngineSwap.htm
http://www.madois.com/html/tech/40swap.html
http://www.mallcrawlin.com/forum/showthread.php?t=6355


Doug Gudmandson
 
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