Hello, after spending a lot of effort to fix all the problems in my S600 I thought I finally have a reliable car. (Including new coil packs, voltage transformer, spark plugs etc.) Until today about 100 miles from home it started to misfire, check engine light. The car refused to move after stopping - no amount of accelerator pressing would get the revs over the idle. After a long time fiddling with a code reader, resetting errors, waiting with engine off etc, finally I got it moving and made it home, car shaking and misfiring along the way. In other words I have enough of that Mercedes V12 as I want to be able to use the car reliably on long trips. I like the S600 - otherwise it is in as-new condition.

I've looked at S550 as an alternative, but nothing compares (unless I spend another $10-$15k on the top of the value of the S600).

So I'm thinking to put in a newer 3.5L M272 V6 (no turbos) with the 7 speed transmission, as available in the W221 chassis outside US. Comfort, engine reliability, easy low cost maintenance, sufficient power and great fuel economy for long trips. Once I get the V12 running smoothly again I should get enough for it to get on Copart an E350 donor.

Engine/transmission mount points should be the same. All the plumbing hoses and exhaust pipes should work after some necessary fabrication. Dual ABC/power steering pump should fit in place of the power steering pump. The rest of the engine accessories would carry over from E350. Of course the toughest will be electronics, but since this engine/transmission/chassis combination is supported by MB, I think it should be possible (maybe requiring buying S350 ECU/TCU from abroad).

Thoughts? Anyone with an experience of making the security system work in MB after similar engine swaps? (possibly a pain if ECU is paired with door lock security etc). Thanks!

 

Following this thread. Interested to see where this process takes you. As you mentioned that the motor and transmission was available in outside countries, I don't see why you couldn't do it. It would take a lot of labor, programing, and time. Along with a very smart MB mechanic.

If you get it working and running, I'll buy you an S 350 badge

 

Is the 6-cylinder any more reliable than the V-12?

I think cost depends how integrated you want it.

Stand alone engine and trans with an aftermarket controller from Holley or somewhere like that can probably be done for $8k or so if you use a used engine do all the install and programming yourself. Figure about $20k if you get it done at a hot rod shop. Everything on your instrument panel won't work though and things like traction control won't work. It will be a hack job. You also might be better off using a 722.6 transmission because it is easier to find an aftermarket controller for it.

If you want it integrated and everything to work like it came from the factory, you will need someone who is an expert in Mercedes electronics and I think you will need a lot of modules from the donor car. I think would be a lot of money.

Finally, if you are dead set on doing this you might want to look at a Chevy powertrain. The cost to fabricate motor and transmission mounts is trivial compared to the integration and programming and Chevy engines are cheap, bullet proof and can be tuned by anyone.

 

Is the 6-cylinder any more reliable than the V-12?

I think cost depends how integrated you want it.

Stand alone engine and trans with an aftermarket controller from Holley or somewhere like that can probably be done for $8k or so if you use a used engine do all the install and programming yourself. Figure about $20k if you get it done at a hot rod shop. Everything on your instrument panel won't work though and things like traction control won't work. It will be a hack job. You also might be better off using a 722.6 transmission because it is easier to find an aftermarket controller for it.

If you want it integrated and everything to work like it came from the factory, you will need someone who is an expert in Mercedes electronics and I think you will need a lot of modules from the donor car.

Finally, if you are dead set on doing this you might want to look at a Chevy powertrain. The cost to fabricate motor and transmission mounts is trivial compared to the integration and programming and Chevy engines are cheap, bullet proof and can be tuned by anyone. They will also be a lot more powerful and nearly as efficient.

 

driving any car where its clearly misfiring heavily is a mistake... even if its a fiat 500 2 cyl air cooled and you have a spare one at home 500 yards away. The misfire damages stuff

going from a v12 to a v8 is backward, but down to a 6pot is going forward?

why not do a compression test on the v12 and then if that pans out is it as simple as buying the other coil pack? What I read was you replaced one, then shortly the other failed and you never did anything about it?

 

@S550e Thanks for the offer to get me S350 badge! That will help :-). @auburn2 6 cyl is definitely more reliable, simply because it's made in millions and has much fewer parts attached to the engine to go wrong. Please just check countless threads on V12 misfiring for V12 problems example. You are right about stand alone though - I've looked at it and rejected this approach - it has to be a "factory" job, done the same way as Mercedes would do it if they offered such a car. It means everything fully integrated. The biggest problem is the immobilizer related circuitry, but it should be possible to program the car's VIN and other security into the 6 cyl ECU, there are a few people around the world who can do this type of work. But any input/advice on reprogramming the ECU and transmission ISM (if needed) greatly appreciated. @BOTUS unfortunately car manufacturers "package" features, so it's difficult/impossible to get in a S350 the same features as in S600 costing over twice as much. So if someone wants a small, fuel efficient engine in a large, fully features W221, Mercedes is not providing it. S350 was never offered here anyway.

With all due respect for the M275TT (the same engine I have is still used with minimal changes in the latest S600/Maybach/Pagani etc and can be tuned to over 1000HP) it is an outdated design created at the time of Mercedes cost cutting. If you look inside it's made quite cheaply (I spent some time comparing it to the previous DOHC V12 which I also have in another car), downsizing to 3 valves per cylinder required double spark plugs, to which ignition was integrated in unreliable way etc.

Regarding misfiring - I would guess that most of the M275 engines are likely misfiring (it only may be damaging the catalytic converter, not the engine, and only until the computer shuts off injectors on misfiring cylinders), but owners don't even know about it. This is because monitoring of misfire is done using a leaky bucket algorithm, so occasional misfire never triggers a check engine light or registers as an error! I've done some experiments watching life stream of engine data over longer periods of time to prove it (until I fixed my car completely not to have any misfires, reported or not)

Mercedes has not been putting any money into development of V12 as they are about to disappear, so if you want to go forward you need to use more modern, high production volume, 6cyl engine like M272, where a fortune is spent on proper design. DOHC, single spark plug, individual coils, variable timing, no turbos, no intercoolers etc - just a simple, reliable and fuel efficient engine with sufficient power to carry W221 S350 0-100km/h in 7.2 sec, which is plenty in normal driving.

So back to the topic - anyone else with an experience in mixing and matching Mercedes parts who could comment on electronics integration? Anyone already driving S350 (petrol, outside US) who can comment on the car experience? Thanks!

 

Nah, fuggedaboutit.

 

Have to disagree with some of the points you make. The M137 was the engine designed and created during the cost cutting period, and was designed as such to meet emissions regulation (following the cessation of the M120).

The M275 was designed to replace the M137 and was simply an exercise of what needs updating on the M137 and what does not. The reason for staying with SOHC and avoiding variable cam timing is really a question of need. The V12 is a low production number engine so it doesn't make any business sense to over-engineer it. Having 3 valves per cylinder has nothing to do with them using twin spark. Mercedes use twin spark in a large number of their engines to determine misfire or in some cases to improve combustion efficiency. The M275 has served as an excellent basis and competes very handily with rival DOHC turbo V12s.

Personally I'm glad they took this approach (or at least them taking this approach is one reason why I have a Mercedes V12 instead of a BMW V12 having exclusively owning BMWs before my current car. It is such a simple engine to work on and mechanically it is straightforward to work with. Don't really follow your 'leaky bucket' analogy but misfire detection is done via ionic charge current. It can accurately determine to what degree combustion has taken place and at a specific threshold decides whether it constitutes a misfire or not - a very intelligent system particularly in comparison to an antiquated crank sensor measurement or knock sensor detection.

I would think if your coil packs are failing that frequently you have another problem which you have not resolved, or you are possibly sourcing your coil packs from questionable places.

Having said all of that, engine swaps are always interesting so I will keep an eye on this thread. It should be very possible to achieve seeing as you are using an engine that is already used in this chassis. Hopefully you find an M272 without balance shaft issues

 

@pillowshot good points, my comparison of cost cutting was not the best, as the m275 was a cost cutting from the previous V12 and the m272 series 3 valve design was a similar cost cutting from the older DOHC 6 cylinder engines.

But without arguing too many points of engine designs, the newer m272 are simpler, more reliable, less expensive to service and more fuel efficient by comparison to m275. I don't think anyone can dispute that.

By "leaky bucket" (term from the data networking industry, maybe automotive industry is using another term) I mean that the misfire counters for each cylinder are increasing with each misfire, but also every so often the counter "leaks" and the counted errors are removed. So if the misfire frequency is low enough, the misfires can continue without the error count reaching the error threshold, and the Check Engine Light NEVER lights up. And code scanning is not showing any errors either. And the driver is never made aware of the misfires (apart from occasional engine shaking, which then is blamed on something else).

And yes, I'm very familiar with balance shaft issues of early cars, that's why I was saying "newer" :-). Balance shafts actually only strengthen the point that m272 was also a cost cutting - instead of doing a L6 or 60 degree V6, both of which are inherently better balanced, Mercedes decided to chop off 2 cylinders from the V8 engine, forcing 90 degrees design and requiring balance shafts.

In summary, I will keep on fixing V12 for now and studying the m272 conversion to get a 100% confidence that all the steps of the conversion will work (will require some months of electronics prototyping, as "theory" is not good enough here :-).

If anyone is ever thinking about switching from V12 to V6 (after being tired of issues or prices to fix them :-) send me a message, so when the time comes, we will have a larger group of like-minded people pursuing the project.

 

That's a little like saying an outboard bass boat is simpler, more reliable, less expensive to service and more fuel efficient than a guided missile destroyer. What you're comparing are two engines so totally disparate, and designed for such completely different roles, that there really is no basis for comparison. It's really easy to "do it better" when you're only tasked with producing half the work. But hey, if you can figure out how to drop in a six-banger and build yourself a one-off, go for it. Resale value will approach zero, but you're not building it for the next guy.

 

Oh I see what you mean by leaky bucket. All cars do this though (modern ones at least). Look up mode 6 misfire counter. Only once the counter reaches a certain threshold (in a given time) will it set the engine management light and associated Pxxx code. If you want to know if your car is misfiring but not setting a code you would need to observe the mode 6 data from the obd. Same as any other "modern" car. At least my BMW from 2005 did it so not sure about older than that.

 

You didn't say why your car was misfiring this last time. Based on you comments I am assuming that you are continuing to have ignition problems after you have done the ignition work or is the engine having mechanical issues?

If it were me I wouldn't consider swapping out the current engine for any other engine much less a different engine model unless you knew it was shot. From what I have observed the 3 valve engines were fairly reliable.

 

I think the current misfire is strictly electrical and not mechanical - some of the red coil insulators were burnt but since some not burnt cylinders were also misfiring I've sent the coil pack for testing/possible rebuilding. So yes, I keep fixing the car for now and would only do the swap once some major problem comes out.

But searching the internet reveals stories where many thousands were spent (including on mechanical repairs) and misfires still continued.

Still I'm interested in the feedback (and contact) if others with the V12 W221 would consider a swap to V6 m272 instead of repairing/rebuilding/replacing the V12

 

@George993 What is your real goal here?

Is this vehicle your daily driver and primary source of transportation? Or is it a weekend/hobby/extra vehicle, and you have another vehicle, motorcycle, bicycle or feet for your daily needs?

 

I have other choices for daily driving, this is strictly a hobby, but I also want to use this car for very long (thousands of miles) trips with reliability. For hobby weekend drives reliability would not matter, but the S600 seems too risky for anything more than a few hours drive away from home. Which is a shame, as it is very quiet and comfortable for long drives.

Normal people would just sell the S600,and buy a Lexus in this case of course :-)

 

I can't imagine anyone else wanting it with a six in it which is fine it you are committed to keeping the car until its ready for the scrapyard.

 

Your car has a CAN bus electrical system controlling everything electrical in the vehicle. Read about those here ...

https://en.wikipedia.org/wiki/CAN_bus

Theres no way your current electrical system copes with a different motor/ transmission.

 

Thanks (actually I had started working with CAN bus messaging a few years BEFORE Wikipedia was created in 2001 :-)