Turbocharger Boost Pressure
 

Has anyone tried checking and adjusting the boost pressure of their turbocharger?

It is my understanding that over time, the boost pressure control valve looses its factory setting (0.6-0.8 bar) and opens too soon resulting in reduced power. Supposedly, the KKK brand is adjustacle but the AE brand is not.

I found the SD to have 8-9 psi when tested. When the turbo was out of the vehicle, I removed the cover and adjusted the wastegate by 3 turns. The boost is now 13.5 psi. The Garrett can be done on the vehicle, but, it's a PITA. Most folks opt for the boost controller to make their life easier.

Brian, any good reference manual for doing this work or would you care to elaborate s'more.

Is 13.5 psi within the .6-.8 bar?
What is a boost controller?
Did doing this impact performance?

13.5 psi is .9 bar.

A boost controller is a device that will regulate the wastegate and is easily adjustable. You can do a search. There's plenty of discussion on it.

Here's the procedure for adjustment of the Garrett:

Turbocharger Wastegate Valve
Spring Tension Adjustment for 617 Engines


Introduction

Garrett Turbochargers

If you have a Garrett turbocharger (w/ wastegate adjustment inside cover), removing the cover takes some time and perserverance. It is not particularly difficult, just tedious. Make sure that the turbo area is cool (use a fan between adjustments) and when re-installing the spring, "squeeze" it to reduce its diameter before inserting. Then, with a screwdriver push on the flat part of the spring until it seats.



KKK Turbocharger

If you have a KKK turbo, the adjusting screw sticks right out of the top (sideways on engine) of the wastegate chamber and does not require removal of a cap.

Caveats

Remember both of these turbos are capable of over 40 pounds per square inch of boost and they run against an open wastegate all the time so these adjustments are really critical. Don't get carried away or you are going to buy a motor. However, please note that it is hard to get a tremendous amount of boost (i.e., well beyond safe ranges) from an original 617 turbo now that the cars have a few years on them now and the springs are fatigued somewhat. Still, confidently proceed with caution.

If you have an exhaust temp gauge in-line you can carry the boost procedure a little further, but even at 0.9 bar (upper limit of factory specifications) they just fly.

Preliminary steps necessary before adjusting wastegate valve spring tension

Prior to adjusting the wastegate valve spring tension, there are two necessary preliminary steps that need to be taken, each of which is provided at this web site: http://hsb.baylor.edu/html/easley/mercedes/mercedes.html and is referenced below:

The first step is to ensure that the injection pump is timed correctly. This procedure is described on the following web page: http://hsb.baylor.edu/html/easley/iptiming.htm
Checking the boost sensing lines and overboost sensing switch is the next step in this process and is described on the following webpage: http://hsb.baylor.edu/html/easley/boostchk.htm
After successful completion of the above two steps, you are now ready to adjust the wastegate valve spring tension (i.e., boost adjustment).
Tools needed for adjusting wastegate valve spring tension on turbocharger

High quality vacuum/pressure gauge (needed for checking boost pressure only)
"T" fitting for vacuum gauge and 6 - 8 foot length of vacuum hose for monitoring boost pressure while driving vehicle (needed for checking boost pressure only)
Phillips screwdriver
10 mm socket and 1/4" drive ratchet and extension for removing air horn
Pliers for removing sensor hose clamps at turbocharger
Small mirror for clarity during cover removal
High powered flashlight or shoplight
Instructions

Remove the u-shaped air intake and the intake to the air cleaner. Make sure to re-install before testing boost pressure.
Cool the turbo area with fan.
Spray the cap cover "spring" area with Liquid Wrench or other similar solvent.
Using a couple of small screwdrivers (a very thin bladed 5-8" shafted one is great), "spin" the spring around until it starts popping out.
Pull out the spring with needlenose pliers or fingers.
Remove wastegate valve cover. Be careful not to damage the rubber seal behind cap (but attached to body of turbocharger) when removing. There will likely be a small quantity of oil that will leak out when the cover is removed; this is normal – not a problem.
Completely remove locknut on wastegate valve.
Make a note of measured length of exposed threads on valve.
Turn spring assembly (it has flat, thin edges for wrench) clockwise. Begin with 3 full turns - it sounds like too much, but it isn't! If our approximations are
correct, for every 1/8" of threads exposed (by screwing spring assembly in),
this equates to 0.15-0.20 bar of boost.
Reverse disassembly procedure. To reinstall spring as easy as possible:
Make sure that you've thoroughly cleaned the groove where the spring
resides.
Make sure that the spring is thoroughly clean.
Lightly file or grind the flat side of the spring at each end so that it's
shiny. This enables you to manuever better when inserting 'cause shiny end
shows.
Make sure that rubber gasket is firmly seated before replacing cover.
Compress spring with fingers to reduce diameter when placing in groove.
And, push cover hard simultaneously.
Then, push spring with biggest screwdriver that you can use. Tap
screwdriver with rubber hammer. You should "feel" spring seat.
Do this only on fan-cooled turbo area.
Road test using Stu's guidelines: having the boost gauge in the car, start driving a fully warmed up motor and engage "S" and go up to 4,000 rpm and full throttle, read the boost. Good luck and hold on to your hat.
If further adjustment is needed, cool turbo area with fan.
Finally

Please let me know if you complete this procedure successfully; it took a while to type this, and I'd appreciate knowing when each person has completed the repair! Please e-mail me at richard_easley@baylor.edu



©1998
Richard Easley, Waco, Texas and Stu Ritter, Denver, Colorado.

I would reccomend the boost controller (google it). In thoery, it reduces turbo lag, and its much easier than adjusting the wastegate.

I opted for the Voodoo boost controller (got it on Ebay for like 15 bones), and it was super easy to install. But make damned sure you've got a guage before you start monkeying with boost.

One thing I'm not totally sure of though, is this: does a boost controller reduce lag as much as adjusting the waste gate manually as Brian describes?

I T'd in a $3 15 psi pressure gauge in my car. hooked it up with some 1/4 poly icemaker line. no lite, but it works fine all day. push 9.75 psi WOT. that is without adjusting anything. I havent even installed my voodooo boost controller.

good word- overboost can cause all sorts of problems. from headgaskets to overheated EGT's. dont mees with it without a gauge.

Wow, mobetta. Trouble with the keyboard? :confused: You usually type much more clear than that.

I'm running 14psi peak boost right now on my high setting, 8psi on my low setting.

When the springs get weak in the wastegate, it allows the wastegate to creep open as the turbo builds boost. With a boost controller, the boost signal doesn't reach to the wastegate until the preset pressure. The wastegate gets the boost signal in one big surge, therefore keeping it closed until full boost is reached.

I'm a bit fuzzy on my turbo stuff, but that's the basic principal.

BTW, I had my 300 spiking at 12 PSI and settling to 11 PSI. I believe cruising at 80 MPH produced 10 PSI. A friend of mine ran it up a mountainous region-in the summer-with the A/C on- at 80-95+ MPH-with 3 passengers and a loaded trunk. It still runs very well with over 250,000 miles, and doesn't burn any oil between oil changes. I think the high end of the MB spec is around 11.X PSI.

There is no need to adjust the ALDA when you raise boost.

When you put more air in you need more fuel.

The ALDA didn't make much difference for me after adjusting turbo because not much boost is produced until about 2400 RPM anyways. Sure I was more responsive off idle but not 15 MPG worth.

You are misunderstanding how the ALDA works.

The bellows inside the ALDA automatically adjust to air pressure. Adjusting the screw only increases the fuel given off the line.

The ALDA enriches the fuel delivery in response to altitude and intake manifold pressure.

The higher the manifold pressure (higher boost)=more fuel needed (ALDA adjustment)

http://dieselgiant.com/mercedesaldaboostsystemservi.htm