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Not real sure but if the engines are different it should still drop right in with the correct engine mounts. The computer and all related hardware would probably have to be changed too, IF they're different engines. If they're both the same engine (my 02 is a 4.0 not sure on the 03-04) it should be quite easy. Definetly possible since the frame on all disco II's were the same. Someone correct me if I'm wrong on this
 

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Not trying to be disrespectful here....

But I think it would be a complete waste of time and money. A lot of folks who have done swaps from the earlier 3.9's to current 4.6's have noticed a gain in power and have extended the life of their aging rover. However, few folks have performed the swap while maintaining no illuminated dash lights. Getting back to the DII, I don't think the minimal gain is worth it.
 

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Swapping just to swap probably isn't worth it. If you have a tired 4.0, then a 4.6 is certainly worth looking into. My truck came with an expired 3.9. It now has a 4.6. I also have another identical truck with the 3.9. I get to compare before and after every day. Apples to apples, the 4.6 gets better mileage. It's a lot more fun to drive. Your foot doesn't need to be sticking out of the front of the truck to get it to move.
Sticking a 4.6 into a 4.0 D2 is no problem. You use the existing wiring and the existing ECU. The problems arise when the 03/04 harness and engine management are used on the older truck. Evap is different. Secondary air usually isn't there on the older truck.
 

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4.0 to 4.6 swap

I have just completed a swap of a 4.0 for my 99 DII with a 4.6 from a 2003. Value is always in the eye of the beholder but from my perspective it is worth it. Quicker response and more overall power is appreciated if you tow especially (in my case a boat and 16' trailer.) I swapped in a 4.6 with the 4.6 wiring harness and the original 4.0 ECU. Had one issue but easily resolved with a little knowledge and help from frickjp. I do not have any SES or other lights on.
 

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Hey Pamos-

If you wouldn't mind could you eleborate a little on exactly what you did. I am thinking a 4.6 swap might be coming up for me in the spring, and was starting to put a game plan together. I was under the impression that I could get a 4.6 block and keep the everything else off of the 4.0 then just maybe swap out the ECU.

Why did you need to change the engine harness? And what was the issue you ran into?
 

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Disco_Stu said:
Hey Pamos-

If you wouldn't mind could you eleborate a little on exactly what you did. I am thinking a 4.6 swap might be coming up for me in the spring, and was starting to put a game plan together. I was under the impression that I could get a 4.6 block and keep the everything else off of the 4.0 then just maybe swap out the ECU.

Why did you need to change the engine harness? And what was the issue you ran into?
Yes, that would be the way to go . . .4.6 with the 4.0 harness and the 4.0 ECU. My problem came from the 4.6 wiring harness that I used (my tech just used it because it was easier for him) It is spliced differently for the evap (the 4.6 engine comes with secondary air that you will take off and plug up) even though the plugs are exactly the same. If you keep the 4.0 harness, it should communicate directly into the 4.0 ECU. The 4.6 ECU will always look for the secondary air stuff (always throwing codes with the SES light on) and that is why you wouldn't use the 4.6 ECU.

I will add that others recommend just using the bottom from the 4.6 and keeping the top from the 4.0 to also minimize possible problems.

I am right now testing the MPG/performance with the 4.0 ECU in there and then I will switch in the 4.6 ECU (which I also have programmed with my security code) and see what the performance/MPG is with that (I assume that the SES lighte will come back on due to the 4.6 ECU looking for the Secondary Air stuff). If no big change then I will have a 4.6 ECU for sale from a 2003 DII.

Hope that helps, Peter
 

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Well now I live pretty damn far from Maine, besides I think ECR is a little rich for my blood.

Peter-

definitely post up what you find, I always thought that I would have to find a 4.6 ECU but if not that would be great. Also have you checked to see if you are running rich or lean with the 4.0 ECU? I wonder how the fueling will be with the 4.0 computer? Let us know if there are any noticeable drops or increases in gas consumption or power between the two ECU's.

Thanks
-Stuart
 

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I don't understand. How can swapping the 4.0 to a 4.6 and gaining the what, 40+ horse power and whatever the extra torque not be worth it?
If my 4.0 ever tires out that's exactly what I'll do.
The torque rating on the 4.0 is 250 lb/ft. What is it on the 4.6?
 

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Roverhound said:
I don't understand. How can swapping the 4.0 to a 4.6 and gaining the what, 40+ horse power and whatever the extra torque not be worth it?
If my 4.0 ever tires out that's exactly what I'll do.
The torque rating on the 4.0 is 250 lb/ft. What is it on the 4.6?

For a 2004my 4.6l, [email protected] and 300lb-ft torque at 2600rpm.
 

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Disco_Stu said:
Well now I live pretty damn far from Maine, besides I think ECR is a little rich for my blood.

Peter-

definitely post up what you find, I always thought that I would have to find a 4.6 ECU but if not that would be great. Also have you checked to see if you are running rich or lean with the 4.0 ECU? I wonder how the fueling will be with the 4.0 computer? Let us know if there are any noticeable drops or increases in gas consumption or power between the two ECU's.

Thanks
-Stuart

Winter is a tough time to do this kind of test but I will see what happens.
 
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