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My M278.8 3.0 Turbo and M276.9 3.5 NA and M278 got the oldie usual fix pulley. No fancy overrunning capability
A2721550515 for both M276.9 and .8 and the M278
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Mine, M276.8. Fixed pulley.
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M271.8 E200/C200 W212/W204 gets what I think is the Overrunning Alternator Pulley OAP
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M271.8 below photo, uses A278 150 00 60 , same as E63 W212
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Other W212 engines using the same A278 150 00 60 AOP pulley. M157 engine is among them.
Note : I never knew there is such a thing as E260
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I am asking this question :
Have anyone seen a fault on this AOP pulley , where it will only work at certain minimum speed/RPM ?
Like a slippery /slipping manual tranny clutch due to wading in deep water and then finally full engagement when the clutch is dry enough.
SuryabI think you're better off without the failure prone ALT pulley. It's only high maintenance item!!
Your tropical heat dictates good A/C compressor + ALT Output ... you need the most robust trouble free setup
You understand what the free spinning pulley does during slow down... your ALT is under enough load with 80Amps it ain't gonna free-spin nothing
The way you like WOT, a set of new ALT bearings may be good maintenance to keep it spinning true, right?
Cali,
This AOP pulley thingy....
Actually I am trying to figure out if my friend's M271.8 C200 W204 with AOP overrunning pulley,
could it be that his AOP pulley is not 100% healthy at lower RPM or an AOP pulley has unique first time engagement requirement as in a bit faster RPM than idle ?
Remember I told you that during during WARM start where RPM is as low as it can get 650-700 RPM, the throttle blip to approx 1,000 RPM-Engine is needed to get the alternator to start charging. Once alternator start charging, keeping low idle 650 RPM is not an issue. Thus now I am thinking of the AOP pulley.
M271.8 gets Valeo 150A, I checked.
If say his AOP pulley is not 100% healthy or has unique first time engagement requirement....and needed that 1,000RPM-engine to start AOP full engagement,
this then is a possible answer as to why the 1,000 RPM-engine throttle blip is needed during WARM START.
Otherwise how and why could this alternator keep charging at low idle RPM ?
Interesting to learn that one-way coupling is used on alternators too...
I had old SAAB 96 model cars in the past and they had what was called "SPRAG" coupling in the gear box. This coupling could be locked with a pull handle in the footwell that made the car behave like the SPRAG did not exist. With the coupling free to work it allowed gear changes (manual) without using the clutch when car and engine speeds were correctly controlled. It did not really work in city traffic but was nice on highways.
This "SPRAG" was remnant from the time when the very early SAAB cars had 2-stroke engines that used oil mixed in fuel. This one-way coupling was a must for those engines as if you let foot of the gas pedal and let car roll you would burn the engine due to fast engine speed but not enough lubrication due to carburetor being closed. The engine had to be able to lower down to idle speed so the SPRAG coupling let car roll faster than engine speed would move it.
Arrie, my family once owned a Saab 900 in early 80s. 2 liter turbo. Odd transmission lock with key in the center console and tranny must be in REVERSE when key is out.
It was manual tranny.
I ruined this car big time as I was only 14.5 years old and naughty.
First car I crashed actually, just minor rear bumper damaged hitting a BMW 520i rear right door because I skidded while overtaking him at a corner.
I was like 5 hours old driver only at that time ... ha ha ha.
Arrie, my family once owned a Saab 900 in early 80s. 2 liter turbo. Odd transmission lock with key in the center console and tranny must be in REVERSE when key is out.
It was manual tranny.
I ruined this car big time as I was only 14.5 years old and naughty.
First car I crashed actually, just minor rear bumper damaged hitting a BMW 520i rear right door because I skidded while overtaking him at a corner.
I was like 5 hours old driver only at that time ... ha ha ha.
Yes, also my SAAB 99 had the same lock for the reverse gear before you could remove the key that was on the floor next to the gear shift. Models 900 and 99 were the same car with everything other than the rear of the body.
Reverse gear lock was to prevent car theft as just jumping the ignition switch would not allow driving the car. The lock for the gear selector was very robust and you could not break the lock. The gear shifter would break before the lock if you would force it unlike steering wheel locks that on many cars could be broken just by forcing the wheel enough.
I remembered this Saab 900 actually already had DAYLIGHT feature in the the early 80s.
Everytime we use the car, other drivers on the road will tell us that we forgot to TURN OFF parking light hahahah.
I read the fuse list and remove the fuse , done.
It has stand alone Daylight fuse.
I remembered this Saab 900 actually already had DAYLIGHT feature in the the early 80s.
Everytime we use the car, other drivers on the road will tell us that we forgot to TURN OFF parking light hahahah.
I read the fuse list and remove the fuse , done.
It has stand alone Daylight fuse.
The 1975 model 96 already had daytime lights. With light switch in OFF position car had head lights ON with half power 6 Volts. You could not drive that car without some kind of lights ON at any time.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Interesting. My 2015 SL400 with the M276.8xx engine has a solid pulley, while my 2014 C350 with the M276.9xx engine has what appears to be an OAP pulley based on the style of the cover.
The 1975 model 96 already had daytime lights. With light switch in OFF position car had head lights ON with half power 6 Volts. You could not drive that car without some kind of lights ON at any time.
Wow, 1975 and they tried Daylight on the main low beam headlight with 6V cut off....brilliant.
After seeing my friends 2,000+ miles driving holiday the last 14 days in Nordic country, I understood now why daylight is very important.
Its all white snow gloomy , pile of snow on the side so high and only road side pole markers available...dang.... zero color for me.
Thanks Jet. Very unque the C350 (M276.957). gets the AOP pulley. I mean it is an M276.9 afterall like in a W212
What formula does MB uses, as what gets AOP pulley ?
Bringing this back up, This appears to be related to the ALT-LIN and how the battery gets charged. All programming logic from the research I found.
OM651 diesel for example. "Smart alternators" started appearing around 2014 for this motor. While the motor was around since 2007 and had a LIN connected alternator, the programming was changed on / around 2014 to further "improve fuel efficiency and emissions" lol. ALT-LIN downfalls started to appear.
Pre 2014, these alternators had OAPs. They were designed with the same fuel efficiency standard in mind, reduced/eliminated drag during shifts and assisted with rapid RPM drops as well as having smoother operation to the motor. NVH and fuel benefits achieved.
2014+ had fixed pulleys but the alternators charge logic was changed to the ECUs controlling it, Supposedly better (on/off switching easily based on environment, braking, accelerating, battery condition etc). When braking the ALT-LIN signal is received to maximize charge and begin induced drag on the motor. With aggressive accelerating charging is off, idle, starting emissions... you can kind of see where this is going.
Happy camper here with the ALT-LIN disconnected but now I have to deal with constantly hitting 1,030 RPM every time I start the car to initiate a charge because of its emergency mode. This diesel also starts quick and idles immediately around 800-900rpm. I also noticed a tiny bit of NVH during small acceleration and when shifting because of the fixed pulley cons of increased drag being on all the time now(although much quicker and smoother thanks to the voltage stability.) Note that my motor and transmission mounts are brand new.
I just ordered an equivalent Alternator with an OAP found on sprinters and other W212/204 etc vehicles optioned without Eco start/stop / battery management etc. Hoping the regulator on this one will charge right away on startup and still achieve some goodness. It also brings up the question about what the ALT-LIN did exactly for the older years. Wish me luck.
Interesting ......... I am really curious for your coming result
The ALT-LIN is basically wire quantity savings, using single wire data bus instead of say 2 to 3 normal wires to do the same work.
As to charging logic being able to be controlled by engine ECM, that is the bonus when and if MB decided to use it.
W204 of 2010 for Indonesian market , M271.8 engine already has this BlueEfficiency dum-azz logic, including radiator air flow grille shutter...can you believe how dumb azz that is in a tropical country ?
Your diesel engine uses glow plug heaters and that is extra 100 amps or so, before cranking and maybe also while cranking the engine ?
That is one hard work load on the alternator when engine already started, it has to claim back lots of amps for the battery for some early minutes.
Have you ever test how many amps are actually needed for your engine + cooling fans as average DC load the alternator have to produce ?
Mine is about 40 amps with AC blower running and radiator fan at normal slow speed, excluding electric power steering of course.
I can check next time through the voltage/amp menu and grab photos.
On my scangauge it does read around 11.8v before starting and as low as 11.2v volt when running before the throttle blip. since I do ctek charging every other week the recovery period is short but still a lot of power. Thinking about a hardwire setup to trickle charge every other day maybe 🤔
Also might be time to change this battery based on your previous threads. This is around 5 years old now.
The car built in AMP + VOLT menu only reads what the battery get as charging amps or discharging amps of the battery, it can't read alternator total gross actual output.
You need stand alone currrent clamp, prefer wireless bluetooth which has Apps you can record and it is very low cost now for up to 100 amps AC/DC.
Like below during alternator load test : 93.1 amps is gross output of alternator and battery is also supplying 15.7 amps, thus the car was consuming 108.8 amps during alternator load test using electric steering. among others.
You must clamp the positive alternator output wire before it enters F32 prefuse box. That is the gross/actual alternator output.
F32 fuses/devices are the consumers of alternator power and battery power.
Battery can also be consumer of alternator power when alternator is at higher voltage than 12.8V , depending on how low the battery state of charge at that moment, it can be up to 25 amps for battery alone.
A non heathy battery is easy to see when ALT-LIN is disconnected, even after driving in a highway ( not stop and go ) for 20ish minutes and AMPS into battery is not under 5 to 7 amps, that meant the battery
is not very healthy.
This is at idling and battery is full , thus 0.2 amps only charging into the battery...
Below is me trying to use baby Owon for Leakage Current test and the bigger OWON as regular current clamp.
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See how I clamp 2 wires using baby Owon. Feed and return wires, while I "leak" out 6 milliamps.
This is how RCCD breaker works too. You are from Europe, they call such breaker RCCD, in USA its called GFI.
Them OWON are so cheap, it is worth it.
Wireless and logging capable makes troubleshooting much easier.
Last edited by S-Prihadi; Oct 4, 2025 at 12:30 AM.
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