Originally Posted by Adi-Benz

Funkwagen said he was considering something like that eventually, he said mounting points were the same and it should even fit I believe.

I'll see if he has any thoughts

Originally Posted by ltwargssf

After some more research, I am almost certain everything fits. The subframes for 4matic and rwd e550s are the same as w204s. My only question left unanswered is the wiring/coding. The engine has its own wiring harness and ECU but would it just plug up to the c300's wiring harness? Coding the E550 engine ECU to recognize my c300 ignition switch/key but I'm not sure if the wiring loom coming out of the m273 will simply plug in to the w204's without further modification. The only additional wires I can think of is two fuel injectors and two ignition coils, everything else appears identical.

Originally Posted by Adi-Benz

Theres more changes to the m276 between those two models than it seems.

I think you can modify the M272 ecu to operate as an M273 but you would need MB STAR

Originally Posted by Funkwagen

Alright so I'm desperately trying to find all my detailed notes on this like I had long ago before I bought a C63, but in short - for right now- is that generally all of the engine accessories as well as cooling setup - are the same between the 3.5L 272 and the 5.5L 273. I have not looked into swapping an M276 to a M273 and I imagine it'll be more difficult as all the facelift models have updated software for the control units and may not include the M273 as a default option for variant coding. Example: cars with eco start/stop, etc, might be harder to swap to.

I do remember that I decided that swapping the entire wiring harness over from an M273 to the project car would be easier than custom wiring - the connectors are the same, the ECU is the same, and mostly everything electrical directly related to the engine is the same. The biggest difference between the two is obviously the wiring for things like spark, fuel injectors, etc etc. So pretty much you take the v6 harness out, and put in the v8 harness and do the required programming in various control units.

I also remember being unable to decide which of a few options are easiest. 1) take an entire drivetrain, including transmission, already mated with the donor m273 and cram it into a w204 2) pure engine swap, needing modification to programming of the ECU which I've been unable to test and 3) engine + ecu swap into 204, which would need to be paired with the original transmission, on the basis that the original transmission is acceptable for the m273 - aka which 722.9 transmission it is - mostly relevant to number of clutch packs, external oil cooling, etc.

Option 1 is obviously the easiest but most expensive. Buying a wrecked w212 e550 would be the best option.

My original goal was to have basically a C550 4matic. From what I remember, cross referencing part #s, LOTS of major components are identical between the W212 and W204 - I think even the front subframe - which means there's room for the front drive train in theory. My biggest concern was driveshaft length/giubo bolt pattern, but I couldn't verify that there was any difference.

As for programming and/or parts compatibility in general, here's what I remember

ECU - Can likely be reprogrammed for M273
Fuel pump - Can be reprogrammed for M273
Evap system electrical - Can be reprogrammed for M273
Emissions - Same electrical, needs reprogramming in ECU and M273 catalytic converters (this was the biggest point on possibly being a tight fit - option to tune out emissions)
ESP Unit - Can be reprogrammed for M273
Transmission - Same as C350, or any model with an external transmission cooler - Needs to be reprogrammed for M273 (cryptic - unknown)
Power steering - Must be parametric/speed sensitive power steering
Ignition lock/Antitheft - UNKNOWN
Front SAM - Can be reprogrammed for M273
Front steering knuckle/axles if wanting to keep 4matic - Appear to be same

Diff ratios should be changed to M273 standard - 2.82. Most W204s are 3.27 (C250 v6), 3.06 (C300) or 2.82 (C350)

Originally Posted by ltwargssf

For the power steering, would that require taking a rack and pinion from a 4matic m273 equipped car or can it be reprogrammed to none speed-sensitive steering? I'm wondering if every model equipped with the m273 had speed-sensitive steering. This would add another part needed to make the swap but I have a feeling it could be reprogrammed to the normal, none parametric rack and pinion and you would just condemn the harness going to the rack and minion.

If anyone here has a Xentry scanner and can check if there is indeed an option to change the engine on the car it would be appreciated.

https://youtu.be/tMQ16j__ot4?t=1012

From this video, I can see an option that would allow you to change the engine the car is programmed too which would allow you to use the C300/C350 ECU but again, I am not sure if the extra wires for the two injectors and coil are in the wiring harness.

Originally Posted by Abass Diya

heyy ! i’m actually interested in this swap, i’m now doing a 6-speed manual from the c300 into my c350 , and need to know if the M273 can be swapped to the manual transmission! btw why don’t we just use the ECU of the M273 when we’re doing this swap ? or it has to be M272 ecu into the M273 engine ?

Originally Posted by ltwargssf

You can use the m273 ECU but you need to find someone that can unlock it and vin code it to your car. 6 speed manual should work but I wouldn't be power shifting it.

Originally Posted by Abass Diya

and is it hard to unlock it ?

Originally Posted by ltwargssf

No, you just need dealer level tool (Chinese C4 Xentry will work fine) and someone that knows the software.

Originally Posted by Abass Diya

aha . and for the wiring and the extras injectors?

Originally Posted by ltwargssf

That shouldn't matter if you use the m273 ECU and wiring harness. Don't quote me on that but from what I've seen, it's a very doable swap and Mercedes are very modular. I'm currently driving my 2008 c300 that I swapped a 3.5L from a GLK350 and everything was plug and play, even the c300 ECU self adapted and runs the 3.5L just find without any reprogramming required.