Question re 124 turbo
 

My 1987 300D/124 (~290K miles) has an inop turbo. This is the fifth turbo on this car. I do not seem to read anyone here with such frequent need to replace/rebuild the turbo. The actuator was not working and the waste gate was also inop. Any ideas as to why this would be happening so frequently?

Do you have harsh shutdowns, as in come off the highway and park the car without idling it for 5 minutes? Are you running excessive boost pressures? Is your IP timing correct? Are you installing new or used turbos, PR are you rebuilding your original over and over? Is the rotating mass balanced perfectly?

Inop in what way? Is it bleeding oil? Is the shaft stuck? There are other conditions that make it seem like the turbo is bad: stuck wastegate, clogged ALDA, etc. Apparently leaky turbos can be caused by blocked drain lines or leaky engine gaskets.

W124 turbo
 

No harsh shutdowns. After leaving the freeway, I go about 2 miles through residential /25mph streets.

I have had new turbos installed twice and have had the turbo rebuilt twice. One other time MB provided a turbo as part of the recall to remove the football filter. I do not know if that was rebuilt or new since the factory/dealer covered it in the early 1990s. The rebuilt ones were guaranteed to have been balanced and tested at high rpm.

I do not know about IP timing but this car has gone through several of those as well. The turbo was leaking a small amount of oil but I would not call it bleeding. Also, the waste gate was not moving but it did free up.

By inop, I mean that when accelerating on a freeway on ramp, the car gets up to ~40mph and no faster although the engine rpm can still go up. The only way to shift is to back off the pedal and wait for a very quiet shift into the next gear up. After that shift, the car can slowly accelerate beyond 60 only if the road is level. Any grade and 55 is about tops. There is no turbo whine at any speed.

Essentially, I can drive the car fairly normally on city streets. Freeways are a challenge.

Does the 124 have a switchover valve like the 126? Symptoms if bad are no power or speed.

So, loss of power. That doesn't necessarily mean the turbo is toast. The first thing to check is that the Alda line is clear. Find the boost tap on the left side of the intake manifold. It's a small hose fitting, which connects with a 2.5mm hose to a nest of plastic tubes. Remove the hose, screw the fitting out of the manifold and check that it's completely clean. The problem is likely right there. If that doesn't do it, locate the Alda at the top of the injector pump, undo the Y fitting. Then plug the Y fitting and use a Mity vac on the boost tap hose to determine whether the path is clear all the way to the Alda, and whether the lines are leaking. (Another quick way to check would be to connect a two foot length of hose directly between the boost tap and the Alda). If the line appears blocked, the problem may be the switchover valve or a blocked line. If it seems to be leaking, the likely reason is a bad rubber connector. The less likely reason is a bad diaphragm in the transmission vacuum amplifier (BUFO).

If the Alda is fine, the problem is wastegate control. It's been a very long time since I've worked on a 603, but I think the wastegate is vacuum controlled. If that's the case, you will have to T in a vacuum gauge to the wastegate actuator to see what's happening. Wastegates can seize, so you want to use a mityvac to work the actuator, while observing the motion of the lever.

X2 ^

How old are fuel filters?

In the 1987 300D, the wastegate should be a fully mechanical unit, no vacuum involved.

Agreed, most likely the fuel filter / fuel supply. Does the idle hunt a little when you come off of the freeway or is it a strong steady idle? Fuel starvation can be from the in-tank filter, the small strainer-filter, or the main filter on the engine.

The wastegate on your car is direct (pressure) actuated, not a very common failure.

Boost enrichment described above will significantly reduce your power to that of a non-turbo. The line from your intake plenum runs across to the bottom fitting of a "switchover valve" near the windshield washer bottle, then another line runs from the middle fitting to the injection pump's ALDA. Failures in this are common, usually the switchover valve, the hose, the restrictor/orifice, or the fitting on the intake become plugged with soot. This can usually be blasted out with WD-40 or another mild cleaner/solvent. The switchover valve is normally open and you should be able to blow through it. Also test to be sure that the ALDA will hold pressure (~15psi/1bar), if it leaks it might not allow boost enrichment. I have not seen this reduce power enough that your car will not shift automatically however, it should still reach 5250rpm no-load and well beyond the shift point under light load. Not reaching this RPM indicates more likely fuel starvation, the engine grows quiet and has no smoke, will not run high enough RPM.

Thanks to all who added comments
 

Fuel filters have been replaced religiously-but I do not know about the in tank filter. I think that I had a mechanic clean it out in an attempt to get the fuel gauge to work properly but that really did not improve the indicator.

I will check all of the suggestions re ALDA, actuator, vacuum hoses, etc. that were mentioned and when complete will provide an update here.

On a different topic, your fuel gauge not working is probably unrelated to the strainer. Usually, it's one (or both) of two things. First, the fuel level sender in the tank. It's really easy to take out and clean, just search for a thread here. Disassemble it, and carefully clean it with electronics cleaner. The wires/sensor get gunked up and don't send the proper resistance readings to the gauge. DIY, ~15 minutes.

The second thing is usually a bad ground in the gauge cluster. Just run a short wire from a screw on the gauge cluster to ground. Did both of these fixes in my car, totally fixed my fuel gauge. It used to be jumpy/sit at empty when the tank was below about 3/4.

the fuel level indicator is different from the strainer. the strainer is on the bottom where the fuel lines exit... unless you have a wagon... then it's all by itself. either way, the strainer needs to be checked...

I solved a poor performing turbo on my 87 300D with a manual boost controller, $20.

The wastegate spring had softened and was opening too easily not allowing boost to come up.

Splice a manual boost controller value into the wastegate hose, and dialed it up.

Now, the turbo gets to its 1 bar boost easily as it should and it restored driving like a "dog" to driving like it should in about 1 minute.

Been driving like that since.