Turbocharger Wastegate Adjustment:
 

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.

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.

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.

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

True.............I installed my boost guage in my car before I used the boost controller.......I adjusted it in driveway but as soon as I hit the street it shot 5 psi past the max I wanted.....(I maxed at 15 in driveway but hit 20 before I coult take foot off go pedal).....had to dial it back again to get it just under 15 psi...........its best to know what its doing real world and not just rely on a breif check with the car stationary.

If you do it briefly like you mentioned, how would you do it? I mean, the turbo will probably not boost to the max, which is where you want it to, without it being under load, will it?

Well if you refer to the shop manual they say to do it in gear with brakes on briefly.....I will say thats total bull....just don't work that way.

Mine was doing 10 psi stock on the road.............

Blipping the throttle you will get boost to peg.....but like I said it pegged at 15 psi with the boost controller after adjustment. I assumed it would need futher tuning...and I was right in less than 50 feet up street it overshot 15psi.

Good example why its important to check boost in real world driving situations. With an accurate guage.

When I set mine in the Merkur, I always did it on the road at WOT. Besides, it was always more fun than blipping the throttle and doing the Hail Mary.

The throttle blip was just to ball park it........... once out of my cul-de-sac there is no shoulder to pull over and its up a hill all the way out in any direction. Wanted it close before I drove it being afraid it might hit 30psi and blow a head gasket.

The electrical over-boost protection circuit will cut the fuel when boost pressure reaches 1.1 BAR (16.1 psi) on the 617 engine.

I have also installed a mechanical 'blow-off' (safety) valve, like the one used on air compressors, to 'pop-off' at 15 psi, just in case the factory system failed.

I have found that welding gauges, particularly the one used for Acyetlene, are not only highly accurate, but also have a 'redline' beginning at 15 psi. This is what I used in the dealership to check/correct boost pressure on customer's cars.

The 617.950 Shop manual recommends removing the air filter element and 'dragging' the brakes to keep engine rpm at 4000 in second to check boost pressure.

I leave the air filter in place and check pressure at wide-open throttle in second gear, with the engine against the governor at about 5000-5200 rpm.

I used to set every 617 I worked on (during a major tune) to 12-14 psi of boost pressure.

On the Garret/Air Research Turbos with the internal wastegate adjustment, 9mm of exposed threads above the diaphragm piston will yield 13.8 psi on a good running engine with a defect-free turbocharger.

Best of luck on your projects...Bert

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

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......

http://www.peachparts.com/shopforum/diesel-discussion/111820-photos-my-w116.html

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