I have this monte with the 3.1, engine threw a rod. My buddy has a 3.8 engine out of a 2003 monte, I was wondering if this would be a pretty simple swap?? Parts and larbor are no problem, unless it comes to fabrication. If it involves a ton of cuttin and welding, then i dont want to stat this. In my head it seems like a simple swap as i seen some 1999 montes with a 3.8 in them. If anyone has any information about this topic please get in touch with me. Im very interested. Thanks Corey.

 

99's are OBDII already, so you will need the wiring harness and the engine, not sure about the transmission tho

 

Yea the trans axle was one of my concerns, i didnt know if they used the same transmission or not, if they do i already plann on changing the flex plate and converter. Thanks for the info, the engine we have does have the harness so im good there

 

You will need to check and verify that the 2003 harness will work in the 99. They are different gens, so the wiring probably changed between the two. You may be able to re-wire it to work if it has the same connector, or you might have an easier time finding a 98-99 Monte Carlo Z34/Lumina LTZ harness and PCM

 

thanks, thats what i was thinking, i just read a post on swapping a 3.4 into a grand am sorta the same concept of what i want to do here. any ideas on the transmission? sorta my last stepping stone before i move any further. Im wondering if i need to re gear it, or if they will bolt up and run fine. did the 99 monte z34 use the same as the 3.1 monte? thanks

 

From what I understand, to swap a 3100 for a 3400 is pretty simplistic. And the transmission on your current 3100 should bolt right up (and from my limited reading, keeping your trans would probably be the better way to go, avoids issues with axels and spacing depending what donor trans you would get).

Here's a PDF that talks about dropping a 3400 in a '95 Grand Am with a 3100. Gives a lot of great info that you should be able to read and adapt to your application:
http://crzyz28.sytes.net/images/bann...swap-guide.pdf

 

The 3800 in the 03 hooked up to a 4T65E and your 99 3100 is hooked up to a 4T60E. In order to swap a 3800 into your particular Monte you will need the tranny, and a wiring harness from a 98 or 99 Z34 (the 03 harness will not work).

A 3400 swap though is just about a plug and play swap. Nothing major needs to be changed.

 

Thanks for the info, that helped me alot, now i know im going to need some new tranny mounts. I shouldnt need tp fab any engine mounts should i? I didnt know if the 3.8 and the 3.1 share? Thanks Corey

 

Mount can be gotten from the 98-99 Monte Carlo Z34 or Lumina LTZ, as it had the 3.8L/4T65e trans.