I will probably be picking up a 91 305 TPI complete swap ecm/harness motor to swap into my 92 3.1 v6. Is it a straight forward swap? I know they run on the same ecm and are very similar. So can I just remove my 3.1 with everything still connected and just disconnect the firewall main harness....remove.... swap in the 305 tpi motor everything still connected as well and just plug that harness into my existing firewall harness?? Swap the prom and maybe wire in a resistor for the vats and I should be good to go?? Or is it more involved than that?

 

The short answer - Everything is different.
The longer, but still short answer - Everything linked to the engine in any meaningful way is different.
The even longer, but still far from complete answer... Yes, if you unbolt enough parts, eventually you get to the point where you can start bolting a V8 back in. The list of parts you'll throw away and replace with the same from the V8 car includes (quick list here, I'm sure I'll overlook a thing or two, but it's pretty much everything)...-
Engine, Transmission, Exhaust system, Accessory brackets, Alternator, Starter, Flywheel, A/C lines, radiator hoses, heater hoses, power steering hoses, motor mounts, fuel pump, fuel lines, engine harness, MEMCAL, Aircleaner + ducting, Battery Cables... Those are all pretty much minimum items you'll need to change. Additionally, the springs, sway bars, steering box, radiator, transmission crossmember, torque arm, etc are all somewhat different. Then you get into the fun stuff that you'd never even think about, like the hard line for the heater core on the passenger's frame rail, the exhaust hangers, the tachometer, the passenger's side front brake line, and stuff like that.
It's not impossible, but no one in their right mind would enter into it, knowing what's involved and the chances of hitting major speed bumps.

Definitely not worth the trouble to swap a 305.

 

By complete swap I really mean complete. Motor, trans, harness, ecm everything exhaust. I'm just wondering if it's a a plug and play with the harnesses and ecm, everything else I will sort out later.

 

Sure. But you'd be furthest ahead to buy a running/driving V8 car. Tracking down all the pieces one at a time is a huge scavenger hunt. You'll spend less on a complete car and it'll save the trouble hunting.

The 3.1 and 5.0/5.7 TPI cars use the same ECM, but you need a chip from a V8 car, and the engine harnesses are different. You should be able to just unplug the 3.1 harness and plug in the V8 harness, but you'll want to verify that the C100 plug has all the wires you need.

 

I have done this exact swap, because a V8 car in Germany is seldom. I found a good parts car. The C100 and C207 are identical, no need to change anything. Just unplug the V6 engine harness and plug in the V8 harness. But that only works with the TPI harness, TBI is completely different. That also works with 91/92 cars/harness only! My car is a 92 and my parts car was a 91 model, so I know it works.
But Drew is right, you litteraly need everything from a V8 car that is diffferent to the V6. Cooling hard line, cooling rubber lines, brake line for front right tire, fuel pump, harness, radiator (yes, they are different), A/C lines... to much to list. If I hadn't the parts car, it would have been nearly impossible for me to do it right, especially because you just don't find good V8 parts in Germany. V6 parts everywhere, but no V8s. Most german people love soft drink sized crap engines I guess...

 

Here you go, a sticky on the engine swap board here:

https://www.thirdgen.org/forums/engi...swap-read.html

RBob.