04'-06' 4.2 engine swap

TLynn731

Original poster
Member
Feb 13, 2019
6
Rochester, NY
hello everyone, my name i toni i have a 04' envoy 4.2 4wd with a blown engine and purchased a whole 06' envoy 4.2 4x4 for a good price with frame rot. i have read alot on doing the engine swap between the 2 and it seems doable but i can't seem to find an exact list of what will have to be changed/converted to do so. also i was wondering what i should do on the 06' engine before it is installed as to they aren't the easiest to work on while installed. thank you in advance for your time and any available help!
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Hi and welcome!

From this thread, found in the FAQ of this section, it is a straight swap with just the change to the coolant temp sensor. That's it.

All I can recommend before installing the engine is to replace the front balancer and rear main seals and install the front diff prior to install. Also, remove the intake manifold for extra clearance. Check the exhaust manifold for cracks.
 

TLynn731

Original poster
Member
Feb 13, 2019
6
Rochester, NY
thank you so much. so there is no need to swap the computer or the fuel rail? the 06' from what i've seen has the pressure regulator in the gas tank and the 2004 has it on the fuel rail
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Yes, you would need to retain your fuel rail from the 04 as well as the 04 PCM.
 

TLynn731

Original poster
Member
Feb 13, 2019
6
Rochester, NY
i finally got around to pulling the engine, trans and transfer case out of the doner 2006 envoy will i have any issues installing all of these components into the 2004 other than the ect connector and fuel rail?
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,045
Brighton, CO
So are you going to swap it as a complete unit? Engine, Trans, TC, and front diff? If so, make sure that the diff gearing is the same, you can check this by looking at the sticker in the glove box, and looking for a GT4, GT5, or GU6. If they are the same imbetween both trucks, you are fine on that. For more, I will leave it for someone that knows more about the 4.2 than me!
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
will i have any issues installing all of these components into the 2004 other than the ect connector and fuel rail?

That's it for the engine. For the tranny, it should swap right in. 2007 is when there was some sort of change IIRC. Transfer case and diff are the same. Just have to be sure the gearing is the same as @TollKeeper said for the diff.
 

TLynn731

Original poster
Member
Feb 13, 2019
6
Rochester, NY
So are you going to swap it as a complete unit? Engine, Trans, TC, and front diff? If so, make sure that the diff gearing is the same, you can check this by looking at the sticker in the glove box, and looking for a GT4, GT5, or GU6. If they are the same imbetween both trucks, you are fine on that. For more, I will leave it for someone that knows more about the 4.2 than me!
Yes, as a complete swap the 2004 had some leaks was the trans and transfercase were still opperatiing correctly but after pulling the valve cover on the engine, the obvious lack of maintenence makes me nervous about the rest and the 2006 is completely dry. all the lines are new in it with delco stickers as well as various replaced parts and every fluid was crystal clear in them. i was actually surprised how relatively easy everything came out i ended up pulling the trans,engine and front diff out as one unit Does any one know of a site that i can decode the vin for RPOs? The 2006 has it scrapped off.
 

TLynn731

Original poster
Member
Feb 13, 2019
6
Rochester, NY
That's it for the engine. For the tranny, it should swap right in. 2007 is when there was some sort of change IIRC. Transfer case and diff are the same. Just have to be sure the gearing is the same as @TollKeeper said for the diff.
ok thank you. i thought that when i had done a transmission in a 2004 trailblazer years ago for a customer that it was one year only so i wasn't sure if that was true or what exactly was different
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
There are lots of online VIN decoders however I don't know if any are able to give the gearing it came with. Maybe GM customer service can help with that. Or you could figure it out with the rear diff:

 
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TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,045
Brighton, CO
You can call the dealer with the VIN of the donor vehicle, and ask them for the gearing.
 

TLynn731

Original poster
Member
Feb 13, 2019
6
Rochester, NY
both vehicle are M30 transmissions and NP8 transfercases. my 2004 is a G80 positraction, limited slip rear axle with GT4-3:73 gears. the 2006 says its GU6 : AXLE,REAR,3.42 RATIO
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,045
Brighton, CO
So you will have to swap out the differentials on the oil pan. A but more work, as long as it separates from the oil pan OK.
 

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