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Unread 06-14-2010, 07:57 PM   #1
nhlnms
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engine compatibility

i have a 1991 4.0 cherokee i was letting a family member use and they ran the jeep without oil and then continued to drive on the highway with the temp gauge at the max. the jeep still starts but runs really rough and will overheat within a few minutes. my parents have a 1998 cherokee with the same motor theyre no longer using. would their motor bolt right in with all the same electrical connections or are there gonna be some differences?

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Unread 06-15-2010, 02:53 AM   #2
CJ7-Tim
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1991 is OBD-I and 1996 or 1997-2001 is OBD-II, so no, it won't just bolt in/plug in. You can use the block and head from the 98 and the fuel injection, throttle body, and other sensors from the 91.

Any running Cherokee is worth more as vehicle than as parts. Why not find an engine from the junkyard and drive or sell the 98 ?
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Unread 06-15-2010, 05:58 AM   #3
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As Tim says, you'll have to take the 98 engine down to a long block, then swap all of your manifolds, bracketry, distributor, sensors etc over. Not a big deal and the motor is free, along with you knowing it's history.
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Unread 06-15-2010, 06:53 AM   #4
lowicz96
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I would rather have the 98 than the 91, or both and find a decent motor somewhere else

dare i say, stroke out the 91 for a trail rig and dd the 98
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Unread 06-15-2010, 06:59 AM   #5
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'91 was the first year for the HO. The '91-95 are basically the same motor. In '96 the did some changes to the block and some changes to the head. The block got some stiffening ribs around the cylinders. The head is also dowel pin located. Still, they are considered HO motors. Physically, it will bolt right. Your sensors should bolt right in from your '91. The only problem that I know of is that the '91 has an extra water temp sensor on the drivers side of the head. The '98 won't have the port for this sensor.
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Unread 06-15-2010, 08:00 AM   #6
nhlnms
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i would just drive the 98 but the body is all rusted. ive been having an over heating issue with the 91 for some reason. i replaced the water pump and thermostat but for some reason the cooland isnt being pushed through the motor. even when the engine is warmed up if i squeeze the upper radiator hose there is no fluid going through it. im unemployed and really dont have the money to put into this thing so im thinking i may just have to sell it cheap and buy a beater. this sucks
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Unread 06-15-2010, 08:37 AM   #7
75SV1
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I don't know the extent of the damage to the '91 motor if any. I would suspect a warped head, if it overheated. The '98's Radiator has an aluminum core. Some say it does a better job of cooling.
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Unread 06-15-2010, 11:12 AM   #8
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swap your head from the 98 onto your block and use your intake, exhaust, injection, etc.
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Unread 06-15-2010, 11:28 AM   #9
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Quote:
Originally Posted by busemans View Post
swap your head from the 98 onto your block and use your intake, exhaust, injection, etc.
You don't need to do this.
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Unread 06-15-2010, 06:02 PM   #10
SemperFi1371
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I have a question, will a head from a '91-95 bolt up on a '90? I have a 1990 4.0 and I'm working on a job that happens to be an engine core reseller but they dont carry the head from a '90 but are willing to give me any head that I want, so im wondering if it will bolt up?
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Unread 06-15-2010, 06:28 PM   #11
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Quote:
Originally Posted by SemperFi1371 View Post
I have a question, will a head from a '91-95 bolt up on a '90? I have a 1990 4.0 and I'm working on a job that happens to be an engine core reseller but they dont carry the head from a '90 but are willing to give me any head that I want, so im wondering if it will bolt up?
Yes, it will. The intake ports are a little different but just use the gasket that matches your manifold and you'll be fine.
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Unread 06-15-2010, 10:14 PM   #12
pentastar01
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I'd make said family member pay for a JY motor, but that's my opinion.
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Unread 06-16-2010, 01:55 PM   #13
75SV1
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Basically, any year Jeep 4.0L head will fit or swap onto any year Jeep 4.0L block. The latter blocks, 96+, used some location dowel in the block to locate the head. I am one of the few who had problems putting a '95 head on an '03 block. Still, I think you are asking if a '95 head and a '90 block would work for you. I woul say yes. The '90 block should bolt right into your chasis etc. The '95 head should bolt onto the block just fine. You will have to align the head onto the block by eye. The bolts will get you close. You could make some aligning sleeves, I guess. One of the bolts needs thread sealant on it. It is torques a bit less than the others. Your '91 intake etc, will match up up the '95 head.
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