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  #1  
Old 03-30-2017, 12:50 PM
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'85 300SD... Engine Bay is a mess, Turbo non-functioning.

I've searched and searched and finally figured some things out...

Quick background, we've had this thing for probably 10 years+ It sat for about 7 years before my brother and I needed a vehicle to drive. After a battery charge it started right up but we noticed it was SLOW. It sat for maybe another 2 years until recently when I decided to make it a project.

Rundown: The engine bay is a mess... This thing is SLOW. I'm talking probably 45 seconds+ for its 0-60. I believe the Turbo does not work, I've never heard it spool up.
It runs fine, starts fine... when it comes to acceleration the pedal is to the floor and the car is less than enthusiastic. It takes FOREVER to upshift, often it requires you to play on-off with the gas to get it to shift.

I believe the culprit is the ALDA and vacuum power changeover valve (I'll refer to it as the VPCV). Remember that part where I mentioned the engine bay was a mess? Well I've attatched a lovely picture of both the ALDA and VPCV. As you can see, the rather nasty hose connecting the two is the only line still connected to the VPCV. I need help because I have no idea what lines are supposed to go there. I have found one line that seems to match to the VPCV that appears to come from the intake manifold. I also found a second line that I didn't check where it came from but it has a small filter on it and is not connected to anything.

Could anyone point me in the right direction of what I'm looking at to get this thing back on track? I'd love to get it running properly but have a long road of replacing hoses and cleaning out grime.


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  #2  
Old 03-30-2017, 12:58 PM
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I would start by making sure that all of your vacuum lines are connected and going to the right places. Find a vacuum line diagram for your year and model and make sure what you have in your car matches it! It's a good time to replace all the rubber connectors at this time too. Rot and porosity are not your friend with vacuum issues.

Next clean out the banjo fitting where the ALDA line connects to the manifold. They tend to get full of soot. If the ALDA doesn't see any boost pressure, you won't get any fuel enrichment.

Make sure the wastegate isn't stuck open on the turbo. Pull the intake tube off and feel the turbo compressor wheel. Try to wiggle it and spin it. It should spin with little effort and shouldn't feel "sloppy".

After fixing the vacuum lines and ensuring your turbo isn't seized, hook up a T fitting to your ALDA line and connect a boost gauge and go for a ride. Under load, you should be building boost around 2000 RPM. If you never build boost or if the boost is very low, you could have a waste gate that's stuck open if everything else seems fine.
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Old 03-30-2017, 01:01 PM
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Awesome, thank you! I'll start with everything you recommended. This is also the first time I've seen where someone also cared to mention where the banjo bolt actually is.

I'll attempt to give an update on my failure or success...
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Old 03-30-2017, 01:04 PM
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Looking closer at your photo above, your pressure line to the switchover valve is broken off. It should be connected where the tape is on that peg sticking forward. With that broken off, you'll never get boost pressure at the ALDA.

That switchover valve is the "overboost protection". In an overboost condition, it opens the ALDA to atmospheric pressure to cut fuel and limit power. Pretty well exactly what's happening here with no boost pipe hooked up!
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Old 03-30-2017, 01:18 PM
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Would this be the correct line to hook to the taped portion? This comes from the exhaust manifold (possibly intake, I didn't look too closely...)
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  #6  
Old 03-30-2017, 01:20 PM
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I say "the correct line to hook up".. I definitely mean is this the correct lead, no way this line is being re-used.
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  #7  
Old 03-30-2017, 01:24 PM
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Yes, that is the line to hook up there. Why not get a fresh rubber tube to plug it in instead of using the tape.
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1999 E300Turbo 405K original miles
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2002 ML320 (Son's)
1998 S320 140K mi (Son's) sold
1985 300SD 311K mi
1984 300D 324K mi (killed by a hit-n-run turd)
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Old 03-30-2017, 01:36 PM
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The tape was not my doing, this was a purchase by my father many years ago, he passed August 2nd, 2011 at 48. I'm not sure what repairs were his doing and what repairs were the previous owner. When he bought it (I barely remember the fine details) it was already in a pretty rough shape. Here I am 21 years old and looking to fix it, partly in his remembrance since he loved the car so much, partly because I think having an old diesel car is cool as hell.

It looks like I'll need a new overboost valve anyways though, I removed the tape and the nipple it attaches to fell apart in my hands.

Edit: And hey, my mom was going to sell it for $500 to a friend of ours who restores older cars and has a Mercedes for himself. I bought it instead.. who can pass up a $500 car like this?
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Old 03-30-2017, 01:41 PM
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Warning I did not spell check any of the below!
The Turbo does not give significent pressure till about 2000 rpms or higher. If it is slow below that the turbo had nothing to do with it.

When I got my 300D it was scary slow but once it was up to speed like on the Freeway it drove normal. When I got off the Freeway when I started from a stop I was back to scary slow.

It turned out the linkages on mine were maladjusted to the extent that the throttle lever was not moving forwared as much as it should have.
Another cause of that can be the bell crank on the fire wall that connects the Pedal linkages to the throttle linkages is no good. The rubber and or the Plastic part/bushing behinde the bracket fall apart.

With the engine cold reach over and grab onto the Throttle Arm on the Fuel Injection Pump and hold it with your hand. Have someone work the Accelerator Pedal and watch the linkages and see how much sloppy play is in them.

The linkage rods have a specific measuerment that you are supposed to start with. Someone will need to post the section of the service manual that deals with that.
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  #10  
Old 03-30-2017, 03:10 PM
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It is called the switchover valve and the car is a real dog without it. I hooked up the lines wrong on my '81 300SD and could not get over 30mph. Corrected the lines and all the power came back.

I will bet that you have great power as soon as you hook up the switchover valve properly.
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  #11  
Old 03-30-2017, 03:39 PM
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To tell if the turbo is working, connect a vacuum/pressure gage to the tube coming off the intake manifold at rear. Its banjo fitting is often clogged w/ crud so fix that too. You can run a nylon tube thru the firewall rubber grommet to put the gage in the cabin or just clip it under the wiper to view thru the windshield. You should see pressure increase as the rpm increases under throttle, up to ~10 psig where the turbo bypass opens.


Read about the ALDA, but I doubt that would be your main problem. It just tweaks fuel flow (by intake pressure above) to compensate for boost, but doesn't have total authority. Many take the ALDA completely off.
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  #12  
Old 03-30-2017, 03:42 PM
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Quote:
Originally Posted by BillGrissom View Post
Read about the ALDA, but I doubt that would be your main problem. It just tweaks fuel flow (by intake pressure above) to compensate for boost, but doesn't have total authority. Many take the ALDA completely off.
100% wrong. If the ALDA is intact, but receives no boost pressure, the fuel enrichment is cut way back. Partly to help emissions, partly to provide a safety if the turbo fails (that's how the switchover valve works).

Removing the ALDA or defeating it will remove the enrichment cutback. With the OP's engine having the ALDA intact, but the lines broken off, the enrichment is in "safety" mode essentially deliberately designed to prevent the turbo from spooling.
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Old 03-31-2017, 12:52 PM
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What I remember the switchover valve being used for from the description in the Mercedes Service Manual is in sitations where you have a high manifold pressure but high load like pulling a trailer up hill it cuts down the(by decreasing the manifold pressure to the ADLA) to prevent you from doing what is calld lugging the engine.

That means that unless you are in that circumstance is met the switchover valve does not do anything in normal driving. That means you can do all the testing you want bypassing the switchover valve entirely.

Not that sometimes the switchover valve itself becomes blocked.

I would like to mention that a Vacuum Gauge can only be used do some checking on the manifold pressure when it is a combination gauge that has a fuel pump pressure gauge built into it.
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  #14  
Old 03-31-2017, 01:10 PM
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Diesel911 - not sure about your comments about lugging but the switchover valve does absolutely affect the way the engine runs. When I replaced mine I got the hoses mismatched and could not get above 30mph. When I switched the hoses, I took it for another run and it ran fine and strong.

So I know nothing about removing the ALDA but I can tell you that with the ALDA working, the switchover valve is crucial. Diseasel300's comment about it being in "safety" mode sounds exactly like what I experienced - although I have never seen that mentioned before.

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