Got the car about 2 weeks ago and even though it had been extremely well maintained it was lacking some boost.

I replaced the boost line, replaced the "change over/boost" valve (near firewall), replaced the line between this valve and the ALDA as well as clean up the manifold boost plug and ALDA plug.
Replaced a small vacuum filter and check all of the vacuum lines for leaks or obstructions.
I replaced the fuel manual priming pump that was leaking a bit, changed all of the fuel filters and air filter.

I can't see any fuel leaks anywhere. I noticed a bit of oil on top of he turbo housing.

The boost has improved a lot but I can tell that sometimes, especially when starting on an hill the boost is lacking somewhat. When I noticed a lack of boost I realized that I was also getting some hardshifts (not too hard but noticeable)(vacuum?).


Any idea where this lack of boost can come from?

1985 300SD, 160k miles, CA emission with service campaign completed in 2000.

Thank you.

F

Checking the turbo wastegate hose might be worthwhile. Also consider adjusting the ALDA.

Check the boost with a gauge, use a "T" off the manifold line.
The ALDA usually is more of a low end problem.
Sorry about the sideways pic.

Attached Thumbnails

 

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83 SD

84 CD

To check the boost off the manifold can I do the test in a static environment by just revving the engine or do I need to locate the gauge inside and take it for a ride?

I'll check the hose first.

Thanks again

Make sure the vac lines on the switchover valve are right. I replaced the switchover valve on my 81 300SD and the new one was somewhat different from the old one - it was a little confusing to determine which line went where. When I installed it the first time and drove the car, I had about zero power. Then someone on the forum let me know that the top inlet is supposed to be open and I had the other lines switched. I removed the plug on the top inlet and switched the lines and got the power back.

Since yours is newer you may have always had the updated valve and experienced no confusion about which line went where.

Just a thought.

Not sure, but rpm are rpm regardless if you're moving or not.
But if you can get one and read while driving, all the better.

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83 SD

84 CD

I bought a long cheap clear plastic tube (water line for the fridge, I think) at Lowes and connected it under the hood and then ran the clear tube in the corner of the hood and thorugh the drivers' window; I kept the window open and went for a ride. Holding the guage in my hand I could clearly see the boost building.... worked well.

Also, have you cleaned out or at least inspected the banjo bolt on the back of the exhaust manifold (towards the firewall on mine)?! Mine had gobs of soot and grease in it that was affecting the boost.

Good luck -
James

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Thank you for all the help.

After cleaning banjo bolts and boost lines and replacing switch over valve etc... I had a valve adjustment done and I can definitively see a difference.
I guess I should do it every 10k or so.

Just for fun (not for the love of speed..) I tested the car, from 0 to 60mph 15.8sec. I guess this is pretty good for that old SD.


F

Whoo Hoo!!

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83 SD

84 CD

Hey guys, I have a related question... I'm going to add a boost gauge by teeing the line between the manifold and ALDA and running it into the cabin. The current section of hose is very old and brittle, so I'm going to replace that while I'm at it. However, I'm having a little trouble finding the correct vacuum hose. I bought a new tee and a few meters of mercedes part # 0001589035 vacuum line, but the hose diameter was too small.

So my question is, does anyone know the mercedes part # for the vacuum hose that connects the manifold and ALDA? Thanks in advance.

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-Brian

1984 300SD, 375XXX miles, Light Ivory w/ Palomino TEX

Get your free one-year subscription here:
http://epc.startekinfo.com/epc/

Fantastic. Did not know about that site, thanks for the info.

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-Brian

1984 300SD, 375XXX miles, Light Ivory w/ Palomino TEX

I used a section of soft copper tubing to replace that hose with rubber hose from the hardware store connecting it to the banjo bolt and a short piece of the old tubing.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Just did the test , T off the boost line from intake manifold to switchover valve.

Can someone help me find the acceptable values for this test.

I got: 5psi at 2500 rpm, 7 PSI at 3000 RPM and 10 PSI at 4000 RPM

Thank you.

F

Found it in the service manual.

At 4000 RPM boost should be [0.7 - 0.8] Bar = [10.1 - 11.6] in