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Old 11-03-2011, 05:31 AM   #1
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converting 4.2 to fuel injection

So I was talking to a friend who is pretty knowledgeable on jeeps about an easy way to make the 4.2 to a fuel injection.
Basically he said you swap the intake manifold, wiring harness, ecm, and injectors from a 4.0 engine. Says the intact manifold set up is the same.
Has anybody tried this? I'm gonna do it eventually when I have the extra money but would like some feedback

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Old 11-03-2011, 12:59 PM   #2
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I have not done a swap on my jeep ('89 4.2L) and have never heard of a conversion that just uses the intake manifold from a 4.0L.

I have read about a swap of the head from a 4.0 to be used on a 4.2L still using a carb. The article claimed you'd gain 35~40 HP. If you convert to a 4.0 head, you'll also need a new exhaust manifold. Be careful and remember, one thing does lead to another!

When I read this article about a 4.2 > 4.0L head swap about a month ago, I was in the process of having my engine rebuilt at a reman shop. When I asked the reman shop about the swap, they doubted whether you'd gain that much HP and also commented on the fact that everytime they send out a Jeep engine that was modified in some fashion; (like swapping heads) there was always trouble. Injectors delivering so much fuel it washed out the cylinders etc.

Instead; I put on a 2100 Motorcraft carb, nutter bypass, the TFI ignition upgrade and I'm very happy w/ the results. A lot less costly and trouble-free. Looking back I'm glad I did what I did as compared to a head swap.

Good luck in whatever you decide to do!

Kahuner

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Old 11-04-2011, 06:42 AM   #3
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I really hate the carburetor, i do a lot of rock climbing so it stalls. I even have a Weber carburetor that pretty new. I gotta do. More research, thanks.
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Old 11-04-2011, 09:22 AM   #4
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What about swapping the carb for a throttle body. The make a conversion for the 4.2 but it's pricey. Between $1100-$1400.
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Old 11-04-2011, 10:09 AM   #5
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you can do this a couple ways if you want to keep the 4.2 you need a 4.0 head plus all the fi stuff or you can transplant a complete 4.0 this is a direct swap if you have the ax15
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Old 11-05-2011, 06:47 AM   #6
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Quote:
Originally Posted by spazinweasel
you can do this a couple ways if you want to keep the 4.2 you need a 4.0 head plus all the fi stuff or you can transplant a complete 4.0 this is a direct swap if you have the ax15
I was told that you didn't need the head
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Old 11-05-2011, 08:19 AM   #7
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The 4.2 and 4.0 heads are different you could get the fi conversion for the 4.2 but it is expensive
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Old 11-05-2011, 10:04 PM   #8
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I have read that you can do a junkyard conversion similar to the Howell system that I have. You will need the throttle body, computer, and the wiring harness from a GM 4.3. Do some searching on line to find all of the details. I bought the howell system a while back and love it. It is a great upgrade.
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Old 11-06-2011, 12:16 AM   #9
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pix

I have from a Jeep show pictures of a 4.2 with the Chrysler FI swap. It's very pricy, but way cool. If I swap my postal, that's the way I'm going. these are actual picture fo a 4.2 with the Chysler conversion.
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How cool is that?
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Old 11-06-2011, 01:22 AM   #10
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Quote:
Originally Posted by yj93ben
I have from a Jeep show pictures of a 4.2 with the Chrysler FI swap. It's very pricy, but way cool. If I swap my postal, that's the way I'm going. these are actual picture fo a 4.2 with the Chysler conversion.

How cool is that?
Me gusta O_O
I'm gonna do it. Is that the same swap as the 4.0 intake manifold
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Old 11-07-2011, 09:36 PM   #11
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I dont believe you can just swap the manifold. You need the head and everything. Since you are going that far you might as well blend the two engines a little more and make a stroker...go big or go home.
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Old 11-09-2011, 07:56 PM   #12
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Quote:
Originally Posted by brightsidememe View Post
Me gusta O_O
I'm gonna do it. Is that the same swap as the 4.0 intake manifold
I don't think so. I was told once that, to use the 4.0 intake manifold, you had to use the the 4.0 head.

Here is a nice article on the Mopar Performance 4.2 MPFI kit; Fuel Injection for Jeeps - Four Wheeler Magazine

But the complete thing is about 3000 bucks.
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Old 11-11-2011, 08:39 AM   #13
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Quote:
Originally Posted by yj93ben

I don't think so. I was told once that, to use the 4.0 intake manifold, you had to use the the 4.0 head.

Here is a nice article on the Mopar Performance 4.2 MPFI kit; Fuel Injection for Jeeps - Four Wheeler Magazine

But the complete thing is about 3000 bucks.
No way I'm gonna do that. Rather just swap the whole engine for that kind of money. I think I came up on a 4.0 anyways. Friend has one sitting in his garage from an 89 Cherokee

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