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  #1  
Old May 2nd, 2005, 07:52
TLange TLange is offline
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Swapping a '91 4.0 with a '99 4.0

I did do a search.

After 190,000 miles of abuse, the motor in my '91 has decided to retire. How do I know this? It's knocking on the side loudly as if to say "let me out"! It's the usual piston slap noise but it has gotten much, much louder within a week. I did check for loose torque converter bolts and cracked fly wheel. They were fine so no such luck.

Anyway, I found a 4.0 out of a '99 XJ. The salvage yard is telling me that it won't work with a '91 because of "issues". Of course he doesn't know what these "issues" are.

Does anybody here know if there are any problems with doing swap like this ('99 motor in a '91)? If it's just peripheral stuff like intake manifold, ignition or etc. I can swap those type of things from the old motor.

TIA!!!
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Old May 2nd, 2005, 08:07
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RichP RichP is offline
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Re: Swapping a '91 4.0 with a '99 4.0

I'm pretty sure the block is the same, issue will be the head and FI setup. Also the 99 may not have a distributor, forget when they went to a 3 coil setup, might be 00 but not sure, I know that 99WJ's had the 3 coil setup sans distributor. Othewise it should be a straight shortblock to short block change so save all your stuff to put on the newer block. Might be a different oil filter too or the way it faces. Might also lack the knock sensor if the 91 had one. About all I can think of....
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Old May 2nd, 2005, 08:32
Goman Goman is offline
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Re: Swapping a '91 4.0 with a '99 4.0

I recently purchased my 91' xj from a Jeep shop. It has a motor from a '00 xj in it. They took the coil packs off the 00' and used the distributor from the 91. Other than that I have no idea what else they had to do.
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Old May 2nd, 2005, 10:51
Vancouverite Vancouverite is offline
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Re: Swapping a '91 4.0 with a '99 4.0

I've installed a '99 motor into a '88 XJ about 3 years ago. I believe '88 to '92 is identical.
Here are the issues that came up:

- Intake and Exhaust ports are slightly different. I bought both gasket set, for my 88 and the '99 engine. One of them fit better than the other. Forget which, but if you buy both...no problems. You can return which ever you don't use.

- The distributor p/u terminals are different. I just took and ohm meter to figure out which wire was which. No problems.

- The '99 was an automatic and the '88 is a 5 speed. I had a hell of a time finding the right size pilot bearing that fits inside the crank shaft to support the tranni shaft. The one specified in the bearing application book did not fit. I finnaly measured the size that I need and asked for it by size.

Minor issues but no problem.
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Old May 2nd, 2005, 11:59
75SV1 75SV1 is offline
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Re: Swapping a '91 4.0 with a '99 4.0

The 91 should be an HO, so the 99+ intake should work. Since you are using the 99 block the serpentine belt drive should work for you. The distributor should swap in. The engine mount bracket bosses should work. I had problems on an '03 block, but the '00 block I have is the same as my '88 for the motor mount brackets. The 99+ heads have smaller exhaust ports. No problem for the swap, but should restrict power a bit. Porting and rebuilding your present head would help. I think the 91-95 head has a sensor hole in it on the drivers side, that later ones don't have. I think its a temp sensor. So putting your 91 head on it might be a good idea. I think there a stick on the JU board for pilot bearings. But it sounds like yours is an Auto. I would use your present flex plate. Your valve cover will fit either head.
Tom
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Old May 2nd, 2005, 12:48
TLange TLange is offline
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Re: Swapping a '91 4.0 with a '99 4.0

Quote:
Originally Posted by 75SV1
The 91 should be an HO, so the 99+ intake should work. Since you are using the 99 block the serpentine belt drive should work for you. The distributor should swap in. The engine mount bracket bosses should work. I had problems on an '03 block, but the '00 block I have is the same as my '88 for the motor mount brackets. The 99+ heads have smaller exhaust ports. No problem for the swap, but should restrict power a bit. Porting and rebuilding your present head would help. I think the 91-95 head has a sensor hole in it on the drivers side, that later ones don't have. I think its a temp sensor. So putting your 91 head on it might be a good idea. I think there a stick on the JU board for pilot bearings. But it sounds like yours is an Auto. I would use your present flex plate. Your valve cover will fit either head.
Tom

Thank You! Yes, it's an automatic. Sounds like the only difference is the temp sensor hole in the back of the head.
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Old May 3rd, 2005, 04:38
75SV1 75SV1 is offline
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Re: Swapping a '91 4.0 with a '99 4.0

I would and am going to use the 96+ front brackets on my swap. I feel since I am using a 96+ block and a 99+ intake manifold, the newer brackets will cause less of a problem. I also got a newer power steering pump. I think this will keep the serpentine belt aligned, than mixing brackets.
Tom
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  #8  
Old May 3rd, 2005, 08:54
aardvark4x4 aardvark4x4 is offline
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Re: Swapping a '91 4.0 with a '99 4.0

I fitted a brand new '01 WJ short motor to my '92 with no problems.
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