4.2 to 4.0 swap? - JeepForum.com
 
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post #1 of 12 Old 04-23-2019, 07:57 PM Thread Starter
Robbiescd
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4.2 to 4.0 swap?

I’ll go ahead and apologize for the threads. My wife says I overthink everything!

As most of you may have read, I have a cracked block. Found a block for $50 so now I have to rebuild.

While looking around locally, I came across a 4.0 that “started smoking” and is for sale. $200 asking or best offer. Is it worth trying to go to the 4.0 vs the 4.2 rebuild? My biggest concern is the electrical. I’m not good at all on the electrical side. My 4.2 currently has the Mopar EFI on it. Spoke with Hesco and they said I would need a new exhaust manifold, but it should work with the 4.0.

My question is, from a cost and modification perspective, is it worth it? Or should I just continue down the road of rebuilding the 4.2?

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post #2 of 12 Old 04-23-2019, 09:43 PM
timatoe
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I'd keep the 4.2 and do the 4.0 head swap when rebuilding.

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post #3 of 12 Old 04-23-2019, 09:45 PM Thread Starter
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Originally Posted by timatoe View Post
I'd keep the 4.2 and do the 4.0 head swap when rebuilding.
Thanks. That’s where I’m leaning also. I’m going to see if he will just sell the head. He may not. Don’t want to get too deep in the pocket book on this.
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post #4 of 12 Old 04-23-2019, 09:50 PM
timatoe
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Right and $200 for a smoking motor isn't a good deal IMHO. If it came with the CPU and harness etc, then yeah.

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post #5 of 12 Old 04-24-2019, 04:32 AM
Que89YJ
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x2 with the 4.2L rebuild. You're going into the rebuild with everything working except the engine. Deal with the devil you do know. Modding is fun to do when you want to, you are dealing with getting it back on the road which is a have to do.

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post #6 of 12 Old 04-24-2019, 07:58 AM Thread Starter
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Good point. I just figured since I had everything out in the open, now would be the time for a possible head swap. But reading his description, it kind of scares me (attached). And I can’t find any other 4.0 heads around. He doesn’t want to part it out, and Wants me to make an offer. Salvage yard wants $200 for the head.
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post #7 of 12 Old 04-24-2019, 08:36 AM
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The 2002 4.0 head was known to have issues. Have you tried using search tempest or car-parts.com?

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post #8 of 12 Old 04-24-2019, 09:42 AM
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I am in the process of doing a 4.2 to 4.0 swap and it isn't that hard and worth while.....BUT...the main reason is to get a fuel injected motor and not spend money fixing up an old carb motor.....or Renix system...you have injection and the 4.2 has more low end torque and frankly I like it better. Which is why my 4.2 will not be leaving my shop and I will save it for another project....

Keep the 4.2 and build it....that is the smart money!!!

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post #9 of 12 Old 04-24-2019, 11:54 AM Thread Starter
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Thanks for the replies. I think your all dead on. I’m just going to get this 4.2 up and running and save my money to one day swapping the old ba10 transmission. I love the low end torque I have, but going up hill on the highway kills me. 5th gear is only for flat roads or going downhill! I’m running 33x12.5x15. Passing a vehicle....forget about it.
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post #10 of 12 Old 04-29-2019, 01:49 PM
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Sounds like you may have the wrong axle gears for the tire size. Can't blame that on the transmission.
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post #11 of 12 Old 05-02-2019, 08:52 PM
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Eh, 5th is pretty tall in the BA10/5, especially with the factory 3.07's. I had the same issue when I was running 29's, 5th was for flat highway cruising, downshift to pass or climb. It IS a tiny bit worse now that I'm rolling on 31's (that's about what my current tires measure out to), but the difference is really negligible. Anything below 65mph and I'm in 4th.

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post #12 of 12 Old 05-03-2019, 11:39 AM Thread Starter
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Same with me. Below 60, 4th gear. Above 60 and when going downhill, I can go 5th. Or if on flat grade. Would have liked to have gone with smaller tires/wheels, but I couldn’t pass up the price. May be an upgrade in the future.
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