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jay_bob · #21 10-11-2019, 08:05 AM

New alternator came in yesterday at the dealer. Valeo factory re-manufactured at the Valeo factory in France. MB logo on the part number label. Looked like a new alternator.

Got it installed last night and car now scans completely error free on the quick test.

I started it with the voltage on the display and it appears the LIN bus connection holds off the alternator from starting its charge until the engine gets up to speed and stabilized (or about 10-15 seconds) after start. So much so that I thought it was not working at first.

Without the LIN connection the alternator just starts making 14.xx V right away. With the connection, the alternator slowly walks up to full output once the engine is stable. So the alternator definitely defaults failsafe on comm loss which is a good thing. It just doesn't have the optimized operation without the comm link.

Some tips for alternator replacement on a 642 powered W211 sedan. I suspect the steps will be similar for the W164 and probably the W221.
- I recommend you go ahead and procure the gaskets and seals on all the joints on the intake tract. If you just put it back together with the original seals you will end up blowing black crap all over the front of the engine.
- You will need E10 and E12 sockets, 7 mm (for Y-pipe) 13 mm (for the B+ terminal) and a T20 bit.
- All references to left and right follow vehicle convention, left = driver, right = passenger (for a LHD vehicle).

- first be sure to disconnect the battery. Put a big note to self not to shut the trunk while the battery is off as the trunk is electrically released.
- jack up and remove front and center bottom covers. You can do the whole thing from the top at least for removal but for replacement you will probably have to work it from below. You do need to be able to unplug the intercooler air hoses from the intercooler to get them out of the way, thus the need for lower access all the way up front.
- Next will be a plastic cover over the belt drive. There are two E10s on top and the bottom is held by a ball and socket plastic tip at the bottom of the cover. Pull hard straight up.
- Take off the triangular resonance pod above the mixing chamber (right side). 3 x E10.
- Take off the left and right intercooler hoses from both ends and remove them to get out of your way. The spring clamps are a little tricky, you just find one end and slide back about an inch or so until it clicks in the released position. This allows you to remove or insert the hose. Then when you've reinserted the hose you just snap the spring clamp back to the locked position. Be ready you are going to get a drop or three of oil out of these.
- Take off the discharge side muffler (down front on left) and the silver tube coming from the turbo outlet. 2 x E10 on the muffler, T20 on the clamp between the muffler and the silver tube, deep E10 on the stud holding the silver tube. Pull the muffler and silver tube out of the car. Mind the o-ring at the turbo outlet, that is probably hanging inside the female end of the silver tube, it needs to be on the neck of the turbo when you reassemble.
- Take off the Y-pipe, the right side air box, and the right side air box intake tube. The left side air box can stay.
- Unplug the glow plug relay B+, glow plug relay connector, pressure sensor (up front on mixing chamber), servo valve (on top of mixing chamber), temperature sensor (behind mixing chamber).
- Remove the two E10s holding the right end of the mixing chamber to the bracket supported by the engine. This is right by where the intercooler return hose plugs in.
- Remove 4 E10s at the top end of the mixing chamber, where it attaches to the intake manifolds. This is right at the center of the V. There are 2 bolts right next to each other at the top of the connection. One holds the fuel hose bracket and the other actually attaches to the manifold. Don't mix up these bolts as they are all different lengths.
- Remove the last E10 holding the mixing chamber, that is on the bracket that also holds the glow plug relay, going into the manifold next to the vacuum pump.
- Grasp the mixing chamber and gently pull forward. It will take some persuasion if it hasn't ever been removed. Gently wiggle and pull and it will come off. More oil drops.
- Remove the bracket that holds up the belt cover (2 x E10).
- Put a 17 mm or a big E-torx (my set didn't go that high so I used a 17 mm) on the end of your breaker bar. On the belt tensioner there is a cast E-torx fitting that is at the bottom of the tensioner assembly. Put your bar there and rotate counter clockwise to release the tensioner. Don't use the bolt at the center, that is the bolt that holds the tensioner to the engine. Pull the serpentine belt off.
- Remove the little bracket that held the tail end of the mixing chamber to the head. 3 x E10, 2 of them are shared with the heat shield over the exhaust manifold. When you go to put this all back together, start these screws but do not tighten them until you have attached the bracket to the mixing chamber.
- Cut the two zip ties holding the wire pack to the bracket above the alternator.
- Using a 13 mm (double check you did lift the battery negative first) remove the B+ connection from the alternator. The terminal cover is probably going to be brittle so be prepared and get another when you order the alternator.
- Unplug the LIN bus connector from the back of the alternator.
- Loosen the 4 E12s holding the alternator to the block. Guide the alternator out the top past the radiator hoses. The bottom rear bolt will not be able to be removed with the alternator in place because it hits the sway bar. Likewise the top rear bolt hits the wheel well. So you will be lifting it out with the bolts still in the pockets.

Putting it back together:
- Alternator back in, remember to pre-load the two rearmost bolts and the bracket before setting the alternator in place. Also load two new zip ties in the bracket while it is out, much easier to do now than once it is in place. 20 Nm on the 4 big bolts.
- Hook up alternator B+, 15 Nm, don't forget to plug LIN bus connector back in. Dress the wire pack and secure the zip ties on the bracket.
- Put the belt back on
- Cover bracket, 12 Nm
- Mixing chamber bracket, these are all 9 Nm, leave loose.
- Mixing chamber, all 9 Nm, watch the harness routing to the glow plug relay. Go ahead and plug everything back in on the mixing chamber. Go back and torque the 3 bracket bolts, 9 Nm on these too.
- Turbo outlet tube and muffler, bolts to block are 12 Nm, the T20 clamp screw is 6 Nm, the stud holding the tube to the manifold is 9 Nm.
- Intercooler hoses, be sure they are inserted all the way, the spring clamp is locked, and they pass the 'tug test'.
- The little triangle resonance pod on the mixing chamber, 9 Nm.
- Belt cover, 9 Nm.
- Y-pipe and right side air box.
- Bottom covers.
- Reconnect the battery. Reprogram the limits on the windows and the sunroof. The clock should set itself once it finds the GPS signal (assuming you have navigation option as most 211s did).

When you go to start it, get in and shut the door. Turn key to 1st position and set the LCD so it is showing '0 mph'. Press and release the instrument lamp dimmer knob 3 times quickly. It should show 'Ub = 12.x V'. Start the engine and verify that the voltage climbs into the 14s within about 10-15 seconds.

If you have Xentry then hook it up and go into Control Units/Drive/CDI 5 - Common Rail Diesel Injection/Guided Tests/Alternator Test and follow the prompts.