Turbo Replacement - PeachParts Mercedes-Benz Forum

kevinaw · #1 12-09-2002, 12:49 PM

1987 300D new owner and new member. Thanks to all for providing the great information about these cool cars. I have been primarily a reader and not posted many questions to date. The forum has helped me solve and investigate hundreds of issues!

Turbo replacement issue. It has taken a while to figure some of this out but initially the turbo was not providing any boost at all as the waste gate arm from the actuator was “modified” by the previous owner to the point of holding the waste gate valve open all the time. Once I repaired the arm the true “characteristics” of this car kicked in and at about 2800RPM you need to hold on! Zero to 60 improved from 30 seconds to about 12 seconds!

The problem is that the waste gate is modified too much for comfort and the turbo makes a lot of noise and weeps oil so much that it is difficult to tell where it is coming from. In addition, it does not spin very freely and moves back and forth on the shaft quite a bit. By replacing the turbo hopefully I will be killing four birds with one stone. I believe the turbo is a Garrett Part Number 002 096 92 99.
I have not been able to measure any drop in oil levels, so I don’t know where the oil on the turbo comes from other than built up over the years.

Any tips on replacing the turbo/waste gate will be appreciated. I plan to replace the oil lines, replace gaskets, change the oil and pre-lube the turbo. I will test the boost but I have no desire to modify it from the stock settings. I have a boost gauge from my son’s RX7. Is the best place to “T” into vacuum line at the intake manifold? The only performance improvement I am expecting is the turbo hitting earlier at 2000RPM and the assurance that the waste gate is working properly.

Thanks!

gsxr · #2 12-09-2002, 03:58 PM

Congrats on fixing the PO's screwup! 12 seconds is factory spec for 0-62mph (0-100kmh) so your car is running as good as new, literally. the Garrett is a leaky SOB, I have it in one of my two '87's and it also leaks oil externally (really annoying). Factory spec for boost is 0.85-0.95 bar (12.5-14.5 psi, approx.) Mine tests at 12.5psi, and if I pinch off the hose so the wastegate doesn't work I saw ~17psi on a test run (don't try this at home, kiddies.) I didn't feel a power gain at 17psi so I left it stock at 12.5. The place to check is to put a "T" in the PRESSURE line from the intake manifold to the ALDA (square thingy atop the injection pump, under the intake.) Pressure to be tested at full load, 4000rpm, in 3rd gear. It should be near full boost by ~2000rpm.

Tip: Disconnect your EGR valve vacuum line and plug it off. Better yet put a sheet metal plate between two gaskets and seal it off permanently. Next, disconnect & plug the line to the ARV (air recirc valve) on the turbo. The ARV kills part-throttle power & MPG and only existed to enhance trap oxidizer performance, which I assume has be removed from your car under factory recall by now. DO THIS FIRST, as disabling the EGR and ARV may just cure the problem you are having with "late" boost!

To R&R the turbo, you will want to buy a rebuilt unit or send yours out to get rebuilt (about ~$500 vs. $1000+ for new). Order the turbo gasket kit from Mercedes (call Wholesale Parts, 800-741-5252; or FastLane) which includes pretty much all the needed gaskets. The oil return only requires 2 O-rings and one flat fiber gasket to the block. It's pretty straightforward but time consuming.

HTH,

kevinaw · #3 12-09-2002, 04:31 PM

Wow, thanks gsxr! Although I had already plugged the vacuum lines to the EGR and AVR I didn’t think to plug immediately at each device. I’m sure the method I used to plug the lines is not completely sealed as there is leakage at the ARV. I performed a test previously posted on the forum to determine ARV failure.

Unfortunately, I already spent time cleaning the EGR out which was perfectly sealed closed with caked-on-carbon. I like your solution to seal it completely as this removes one more variable.

I'll try this first to see if it helps. Thanks again!

kevinaw · #4 12-11-2002, 03:22 PM

Thanks gsxr, The tips you provided were right on target.

After plugging the EGR and the vacuum outlet on the turbo the results have been an earlier turbo hit at about 2200. This has improved shifting (much smoother) and de-accelerating (speed falls much smoother). I’m not sure if I would characterize the turbo coming on as a “hit” anymore either. It is still powerful, but overall a smoother transition. I’m sure with the AVR in the loop before was allowing some leakage.

Possibly unrelated to all of this, there seems to also be less smoke at startup. Something else I was trying to cure with new glow plugs and injectors etc. I had only experienced marginal improvement prior to your fix.

Thanks again!