As many of you know, there are two types of turbos on the 617 engine. The KKK turbo has an externally adjustable wastegate and the Garret/Air-Research turbos have an adjustment that is concealed under the cover.

Since the KKK turbo is easy to adjust, this post will detail the correct adjustment of the Garret/Air Research style wastegates.

Prior to this modification, you need to check your boost pressure in accordance with Mercedes-Benz service recommendations. You should also ensure your engine is mechanically sound and the turbocharger is free of any defects.

Keep in mind that you should never exceed the boost pressure specification for your particular engine.

Record the amount of boost pressure and compare it to the manufacturers specification. The difference is the amount of boost pressure you will need to dial in.

Now, on to the removal of the diaphragm cover and subsequent adjustment.

The cover is retained by a flat, circular snap ring that is easily removed with a pocket screwdriver. The ends of the ring have a small cutout that can be easily pulled outward with the screwdriver. Once the end is removed, simply rotate the ring out of the groove in a circular motion.

You may find the cover is partially filled with engine oil. Don't be alarmed as this is normal on higher mileage engines. Clean the area with Brake Cleaner and blow dry with compressed air.

On top of the rubber diaphragm, you will see a threaded stem and a 8mm x 1.0 lock nut with a 13mm hex. This is where you will make your boost adjustment.

The threaded stem is actually the wastegate valve stem. If you look closely, the stem is hollow. This serves as a pressure bleed and prevents 100% of the boost pressure from acting on the diaprhragm. Shoot a little spray cleaner into this opening. If it is clear, the fluid should run out the rectangular opening in the side of the diaphragm housing.

You will need a very thin 14mm end wrench to grip the flat areas on the metal portion of the diaphragm piston. You can purchase a special wrench from Snap-On, or grind one down to meet the needs of this service procedure.


Once you have gripped the diaphragm piston, loosen the 13mm lock nut and remove it from the wastegate valve stem.

Now, you will need a machinist's ruler to measure the amount of threads above the diaphragm piston. These are the little steel rulers, approximately 6" in length, available from all tool suppliers and many auto parts stores.

The stock setting for the wastegate will be approximately 7mm (.275") of exposed threads above the top of the diaphragm piston.

The threaded stem of the wastegate valve is 8mm x 1.00 pitch. This means each full turn of the diaphragm piston will expose another 1mm of threads.

With a popsicle stick (or suitable non-metal tool) gently pry the rubber diaphragm away from the housing in a circular motion.

Now, with the thin 14mm wrench, turn the piston clockwise (CW) the approximate number of turns required to reach the desired boost pressure.

Each full turn of the piston will result in 1.0mm of travel and an increase in boost pressure of about 1.0 psi.

Each 3.0mm of piston rotation (CW) will yield approximately 0.15 to 0.20 BAR of boost pressure or roughly 2.25 to 2.94 psi.

If you have the turbo apart and would like to test wastegate function on the bench, you may elect to use the following procedure.

You will need to remove the 4-bolt cover over the back of the wastegate valve and have the 8mm x 1.00 lock nut removed from the valve stem. The cover will need to be replaced so you can use shop air pressure on the diaphragm to simulate boost pressure.

The steel shim gasket is available from most turbo repair shops, such as Turbo City in Orange, California. However, it can be reused if it is not broken.

Take the Acetylene Gauge (0 to 30 psi) from a common set of welding regulators and attach it to a paint gun air pressure regulator with a common 1/8" Male Pipe to 1/4" Female Pipe Reducer Bushing.

Now, apply regulated air pressure to the (assembled) diaphragm housing and record the pressure reading when the wastegate valve begins to move off of its seat.

Correct adjustment (stock setting) will be acheived when the valve is fully closed at .69 BAR (10 psi) yet begins to open at around .70 to .78 BAR or roughly 10.3 to 11.2 psi.

The valve should be approximately 13.0 to 14.0mm (.500" to .550") off its seat at 1.0 BAR (14.7 psi) of boost pressure.

Keep in mind, this will approxiamte the factory setting and I recommend you always measure boost pressure and threads above the diaphragm piston before making any modifications.

Due to the different skill levels of the automotive hobbyist, I can assume no liability for damage and/or injury for misuse/misinterpretation of this service data.

I hope this information is helpful. Best of luck on your projects...Bert

If this seems to difficult/ too much work for you, buy a boost gauge please!!! It is adjustable with a hex screw and installs to the system with very little effort. Here is a picture of mine.[IMG]Cardomainpictures078[/IMG]

Thanks for the wonderful informative FAQ. It should become part of a sticky.....hint...hint.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

What about this? I have used it on an 89 Merkur XR4Ti and I found it works wonders. The Merkur used a Garret turbo and as the boost climbed, it would bleed off part of the boost to the controller so it opens the wastegate a little. This made it boost slower. When I installed the unit, I could control the boost pressure. More importantly, the boost pressure would build up much faster till it reached the set pressure and then it opened the wastegate.

__________________
01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

I run a simmular one........and believe me you NEED a boost pressure guage....its way easy to excede the max. With any sort of adjustment its very critical to know exactly where the boost is. The Garrette T-3 is easily capible of far more boost than the engine can handle.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

IMO, only a moron would tweak the boost without some sort of gauge that is accurate.

__________________
01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

I will install a boost pressure gauge in my W116 as soon as I can find a place to put one that looks like the factory did it...Bert

Hey,
Could you use a mity-vac to check boost pressures or is it not sensitive enough?

Danny

__________________
1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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I wouldn't. I would get a boost gauge. They are not that expensiv.

__________________
01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

Bert if you are a non-smoker do what I did........make a panel that replaces the ashtray.........I put a boost, Pyrometer, and Voltmeter there...all 2 and 1/16 guages.

Here is my post with pictures of my car......

Photos of my W116

......the last picture shows my guage panel.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I got the $17 boost pressure guage from JC Whitney. I was only planning on using it to test boost pressure, not permanently mounting it. It's kinda cheesy but it works. I guess anything that measures pressure would work for testing, as long as you're confident of the accuracy. You could use a modified tire guage in a pinch.

__________________
'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)

BEAUTIFUL WORK!!! I like this very much!!! How much modification is required and what did you use as a bezel to mount the gauges???

Also. I favor 360° gauges and it looks like at least one of them is that style. What gauges did you use and where can they be obtained???

Where did you tap into for the pyrometer???

I think just a Boost and EGT Gauge would be enough for my W116. Maybe a wood bezel could be fashioned and stained/laquered to match the other trim pieces???

Love the euro lights and bumpers...must have them someday on mine.

Thanks for the input!!! You have inspired me!!!...Bert

Sorry for the belated answer.....I missed your last response.

I got a piece of aluminum, mocked it up to fit where the ashtray was....I then centered the 3 guages on the panel...this it critical as there is just barely enough room for all 3.

Used a hole saw bored the holes...dry fit it to make sure it worked.

I did have to cut away at the plastic behind the ashtray....use a dremil cut off tool.....trust me. And don't go any deeper than needed with the tool.

I then cut a piece of textured ABS plastic and epoxied that over the aluminum. its more durible than textured paint as I see it. A zebrano panel would be aces if you have the skills.

the rest you can figure out. You need to be creative to hold panel in however.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche