Engine swap information

2004 DODGE RAM
100,000 MILES • 3.7L • V6 • RWD • MANUAL
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EASLEY127
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  • 3 POSTS
I have the truck listed above it is the 1500.The engine started knocking. A friend has a 1999 Dodge Ram 1500 with the 3.9 L. will the 3.9 L fit in the 2004 Dodge? I I have been looking all over the Internet and asking around but no one can answer me. I was told it would fit but I would have to take transmission drive shaft, rear end, computer and wiring harness, but do not know if that is true. any information would help.
Jun 30, 2017 at 12:04 PM
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STEVE W.
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  • 15,362 POSTS
Will it fit? Yes. But you would have to change out all the listed parts plus the fuel tank, BCM, dash and harness plus steering column and probably more because the programming in the parts has to match or it will not run.
You would be farther ahead to just get a re-manufactured 3.7 for that year if the body and transmission are in good shape.
It used to be simple to just swap out the engines in vehicles but with all the computers and modules in anything past about 2000 it is not easy anymore.
Take that 2004 3.7 They changed the sensors and internal parts after the 2002 and 2003 versions so that it will work in the 2004 and 2005 vehicles, but 2002-2003 are different and 2006-2007 are different as well and not interchangeable.
Jun 30, 2017 at 12:37 PM
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EASLEY127
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Thank you.
Jun 30, 2017 at 12:46 PM
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STEVE W.
  • ✓Experienced Mechanic
  • 15,362 POSTS
You are welcome. Sorry it is not good news, but the way they build them these days about the only way to do a swap takes a bunch of extra parts and someone to deal with the computers.

It is possible to put the 4.7 in there, for that you need the engine, correct mounts and the ECM for it. But the 4.7 is not the most reliable engine either and for that year they are not that much more powerful either.
Jun 30, 2017 at 3:39 PM
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EASLEY127
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I will just go buy a crankshaft kit or go to the junkyard and see if I can find a good engine.
Jun 30, 2017 at 5:01 PM
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