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  #1  
Old 08-20-2012, 01:21 PM
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'92 300D - Turbo not working

I have two '92 300D 2.5 Turbo's - one with 197k miles and the other with only 92k miles.

Both are new to me (few months) and it seems clear to me that the turbo is not working on the 197k car. The engine revs up and you never feel that "pull" you get when the turbo kicks in (like I feel in the 92k car).

What are the basic things I should check?

Thanks,

-John

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  #2  
Old 08-20-2012, 01:56 PM
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Check that there's a clear line from the intake manifold to the square thing on top of the injection pump. Depending on the vintage of 2.5, the line from the manifold can go through solenoid then split to the square thing and a pressure sensor, or there won't be a solenoid. You should be able to blow air in one end and out the other. Run a pin or wire through the manifold fitting to make sure it's not gummed up. You can remove the fitting on the square thing to clean it but don't poke into the square thing. Don't apply a vacuum to the square thing. Square thing is the technical term for what most folks call ALDA. ALDA is the search word here but it's debated on a dozen threads daily so it's hard to find definitive guidance.

Check that the vacuum line to the wastegate actuator isn't leaking. Also check that EGR wasn't disabled using a blocking plate or plug in the vacuum line.

Depending on what you find, this might be the simpler path - http://www.peachparts.com/shopforum/diesel-discussion/212097-wastegate-actuator-swap-om602-962-a.html

The downside of the modification is you pretty much have to do it yourself. A self-respecting shop shouldn't tamper with the emissions system.

Sixto
87 300D
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  #3  
Old 08-21-2012, 10:07 PM
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Read this post. Just went through something that seems similar.

http://www.peachparts.com/shopforum/diesel-discussion/323075-help-local-mb-mechanics-cant-figure-out-my-car.html


I would advocate to do the wastegate swap suggested by sixto. Read the link he provided a few times to understand it thoroughly. At some point if you are like me it will all click in your head and become trivial. It will cost right around $100 and not hard to do once you get in your head what you are effectively doing. You'll need to order 1 part, and the rest is just lowes/home depot/autozone type of fittings and tubing.

Might start with installing a boost gauge, probably another $50 and a few hours to do (mostly the hard part is finding a place to mount the gauges). That will tell you what's going on once you do get things working although you'll feel it for sure anyway. May as well drop in a vac gauge at the same time (OK another $50) and mount them both in the ashtray space. Great place to locate the two gauges in the w124 and it will look very clean if you are careful and you can illuminate the gauges to work with the headlamp switch using the ashtray lighting wires. Here is a youtube I put up with at least some highlights of that.

W124 Mercedes boost and vacuum VDO gauge installation - YouTube (sorry for the poor quality but it may help with some ideas)
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Old 08-22-2012, 07:50 PM
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I got some time to work on the car tonight.

I replaced the vacuum line to the wastegate and pulled everything from the ALDA to clean it with brake fluid. I also tested the wastegate with a mightyvac and I could feel the gate open/close - so that seems to work.

Put everything back together and no change. I then pulled the vacuum line off the ALDA - still no change.

Does this mean something is wrong with the turbo itself?

-John
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  #5  
Old 08-22-2012, 08:00 PM
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You haven't eliminated a couple of potential problem areas:

1) Inoperative ALDA = easiest way to acquit it is to remove it temporarily

2) EDS not closing wastegate = run a vacuum gauge to the cabin so you can check

Sixto
87 300D
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  #6  
Old 08-22-2012, 08:03 PM
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So - when you say "remove the ALDA" does this mean physically remove? I thought pulling the vacuum line off it was enough - sounds like I need to physically remove it?

In regards to the EDS - I'll do as you suggest and see what happens.

Thanks again!

-John
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  #7  
Old 08-22-2012, 08:05 PM
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unlikely that there is anything wrong with your turbo,follow Sixtos advise and change to a pressure operated wastegate control.On the passenger side of you engine compartment there are several troublesome components that you can eliminate and save yourself a bunch of future headaches.That system is just not worth the aggravation it causes.
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97 E300D 157000 miles
87 300TD ?141k? miles
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  #8  
Old 08-22-2012, 08:18 PM
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The ALDA is a fuel inhibiting device. It assumes there is no boost until the boost signal proves it wrong. If the aneroid capsule leaks, it has no way to respond to the boost signal so it sits there with its finger on the do not enrich button.

Sixto
87 300D
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  #9  
Old 08-22-2012, 08:30 PM
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Ok - I put a vacuum gauge on the vacuum source going to the wastegate and went for a drive and pushed the engine hard trying to get the turbo to engage.

When the engineer first starts there is a moment of vacuum then the needle went to zero. The needle stayed at zero during the entire drive - not moving. Once I stopped and shut the engine off the gauge showed a vacuum which slowly bled away.

Sounds like the EDS not sending the correct signal to the vacuum source?

-John
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  #10  
Old 08-22-2012, 08:33 PM
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Sorry - getting late.

"When the engineer first starts" -> "When the ENGINE first starts".
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  #11  
Old 08-22-2012, 08:43 PM
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Run a vacuum line directly from the vacuum pump to the actuator so the wastegate is held close. In fact subvert the line that supplies the vacuum devices on the passenger side of the engine. A drive around the block should confirm the engine can make power. There's little to no risk of blowing the engine if you don't keep your foot to floor.

Sixto
87 300D
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  #12  
Old 08-22-2012, 08:46 PM
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Could also be the transducer that converts the EDS' electrical signal to a vacuum signal for the actuator is bad. I don't know what voltage signal the EDS sends the transducer. If you're up to it, run a test light to the cabin to see if the EDS is communicating with the transducer.

Sixto
87 300D
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  #13  
Old 08-22-2012, 08:59 PM
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Funny you should mention the transducers.

The vacuum line between the transducer that controls the Intake flap seems to be acting oddly. When I first bought the car a month ago the vacuum line between that transducer and the Intake flap actuator was disconnected. Thinking it must have just come off the transducer I plugged it back in and did a test drive. The car was smoking and coughing like crazy. Upon closer inspection with my "working" 300D the Intake flap actuator was not fully engaged at engine startup - where my "problem" 300D had the Intake flap fully engaged. Pulled the vacuum off (like I had found it) and the Intake flap went back to its resting position and the engine was fine again.

The reason I bring this up is perhaps this is all related to the EDS? I'm assuming the EDS controls the Intake flap as well as the wastegate.

Either way - I'll try your suggestions tomorrow. Thanks!

-John
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  #14  
Old 08-23-2012, 08:24 PM
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Ok - here is what I was able to do today.

1) I read the entire 20 page thread on the wastegate upgrade you mentioned. I ordered the parts today - sounds like an easy DIY.

2) I took the vacuum line (which reads 20 [not sure the units]) that feeds the entire passenger side and plugged it into the wastegate vacuum hose as you suggested. I was able to confirm the wastegate did open. Took the car for a drive and no change when pushed hard.

3) I took my MightyVac with me in the car with it connected to the wastegate and pumped it up to 20 [not sure the units] and pushed the car hard - no change.

4) I tried #2 and #3 with the ALDA connected and with it not connected. No change.

Disappointing... I'm sure the turbo is not kicking in - I have another '92 300D 2.5T and it's clear when it kicks in around 2200-2500 RPM.

Any more ideas? Starting to think it's the turbo itself??

-John
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  #15  
Old 08-23-2012, 08:37 PM
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We're expecting the wastegate to close. The spring in the actuator holds it open.

It's disappointing that nothing happens with the ALDA connected. We don't expect anything resembling power with the ALDA disconnected. We hope you can test the car with the ALDA outside the engine bay. That will tell you if the turbo's working.

Sixto
87 300D

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