Sunday, June 21, 2015

W126: The BlackBastard, Vacuum

After today, the pads of my fingers are worn to the bone. There are so many small fasteners on the engine that my fingers became the ratchet.

The Mercedes M116/7's are notorious for having hidden vacuum leaks. It doesn't help that the owners of these engines don't realize how much of the vacuum system is actually hidden away underneath the air cleaner and then underneath the air flow meter. The meter boot being just about the #1 source of vacuum leaks and odd idling, high idle, etc. The work to replace it is easy, but tedious. Once you've got it down, you can get the air flow meter boot replaced in about 45 minutes to an hour....unless you've got a 6.0L DOHC M117. Then the time is 45 to an hour with a hour thrown in trying to get the damn boot to seat because you hadn't realized the guys at AMG trimmed the boot slightly.

So we start out with the unicorn in relative completion. I have the fuel injectors out for cleaning, so tampons and paper towels were stuffed into their holes to prevent debris/fasteners from falling into the depths of the engine.


Good ole AMG valve cover

Once you have the injection lines removed from the injectors, remove the two fuel lines that feed/return the fuel system. The line size is 17mm - a swift hit with your palm will usually break them free, if you're struggling with it, get a flare nut wrench on them so you don't strip them. There are 4 10mm fasteners on the 4 corners of the air flow meter, a couple electrical connections (EHA, AirMeter Potentiometer), and the absolute IDIOTIC boot to throttle body clamp.

With a little pulling, the bastard's stomach is removed.

This is why these cause so many people trouble, this car at 75k miles has a lot of cracking - no one will escape the crack wrath.

More cracking here.

Now we're getting into some deep s.....

You're walking down the street and someone offers you some crack....

One the bright side, this is CLEAN compared to a lot of other cars I've done this work on. Which is fantastic, the engine isn't blowing oil into the intake

Bunch of 10mm fasteners removed the boot locking plate in place. Reassembly is backwards.

Now we're getting into the fun stuff. Somebody stuck some sort of A M G intake manifold on the engine? Anybody know what the letters mean? Maybe some sort of oddball casting from some company in the 80s that built some fairly potent V8 engines?

Clean engines are happy engines. Under air flow meter house keeping

Prepping everything to be cleaned. A few gallons of acetone evaporated during this process.  

This next picture will give you a good idea of how the next hour went in trying to seat the new air meter plate.

Turns out the slick sumbitches shaved down the boots strengthening rib to fit around the beefed up intake manifold.

Here's a closeup of the shaving done. Mine wasn't anywhere near as pretty for the limited tools available. Note: Keep drill handy at all times.

Got the boot seated, whole air flow meter assembly is bolted down, time to throw on the freshly cleaned injectors with new seals. They're looking mighty nice in there.

Clean engines are happy engines. Clean engines make people who work on them happy too.

Got just about all the vacuum pieces installed. ICV hoses, breather hoses, etc

At some point, a set of spark plug wires was put together. Turns out rather than spending $300 some odd dollars on a wire crimping tool, I had one that does essentially the same thing, for a fraction of the cost.

Clean, nicely routed spark plug wires.

Wires got new boots and ends. New plugs were installed along with a new cap and rotor.

I haven't seen an air cleaner on this engine in a long time - almost complete.

Drove it around the storage facility a bit. Had to bleed out a bit of air from the brakes too as the pedal was mushy once the engine was started. Don't mind the filth, she'll get washed.

The money shot.

Anyway, that's all I've got for now - this is one of the longer posts I've done. Some 12 hours later, the pads of my fingers are still numb. Have had enough looking at this car for a while - needs to be driven around a bit and sorted out slowly.

The more labor put into it, the more of an amazing deal this car turned out to be. A lot of folks with a lot to say about it, but nobody with the decency or money to go and actually look at it. The history that came with this car surpasses anything I've ever seen. It'll make a great driver and track rat once again.


  1. Thank you for your digalance you just helped me understand why my 85 380se stalls after it warms up till i push down a little on the throttle plate. I was wondering where the vaccum leak was.

  2. This has got to be the best and most informative post I have seen in a long time. Well done.

  3. nice write up...where is this car now