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Difference in 06 5.3 VIN Z and 04 5.3 VIN Z

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I have a 06 5.3 vin Z with 240k+ miles and have found a few 04 VIN Z engines with low miles. What are the differences in those year of engines? I also have found a few 04 engines that are not the flex fuel 5.3. Will these work in my truck as well? 

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Flex fuel required changes to the fuel system to support alcohol. So fuel tank, lines etc where I upgrade to remove rubber etc.

Nearly all engines will support e10,e15. However, if you are trying to run E85, you need an engine raged for such. The engine will support higher compression to needed for the lower btu fuel.

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Z just means larger injectors on those trucks and then of course upstream of the engine more stainless to handle the ethanol along with the programming and the alcohol sensor.  Mechanically the L59 (vin z) and the LM7(vin T) are identical and can be swapped vice versa.  Put your engines intake on an LM7 long block and voila...its now an L59.  The only 5.3 in the truck that actually differed was vin B being the L33 which had flat top pistons, 243/799 heads and an aluminum block.  Those are only found in 05 to 07 extended cab trucks.  


If you want to be really technical an L59 in 04 may or may not have press fit pin connecting rods whereas an 06 will only be the full floating pin connecting rod.  Does that matter to swapping?  Nope!

Edited by SierraHD17

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