1987 300D Turbo Charger pressure

I got a 87' 300D about a year ago. It had been sitting for several years I didn't know what to expect as far as power was concerned. Changed all the filters, and used the mercedessource injector cleaning system. The car ran much better. But still very sluggish. I hooked up a gauge to check the boost pressure. Im using original mercedes diesel engine sevice manual. It says that under full load at about 3500 rpm's I should have between .85 -.95 bar of pressure. All my gauges read in psi. When I converted .85-.95 bar to psi I get 12.32 -13.77 psi. Is that correct? Do these turbo's put out that much pressure.
I'm only getting a max of 3.75 PSI which is normal for american car engines.
So can some one tell me if this is suposed to put out 12-13 PSi of boost?
If it is supposed to put that much out do you know where is a good place to get a rebuilt or new one?
Thank you very much for any help.
Art D A+ Machine.

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Diesel Engine Specific Aid

Chassis Model Number

W124

Possible problem spots

In all my years of working on Mercedes diesels I have only had to replace a couple of turbos. Low boost pressure does not necessarily mean the turbo is bad. If you understand the principles of turbo operation there are a number of other factors to consider. A lean fuel mixture or incorrect injection spray pattern and or improper timing can lead to the symptoms you describe. In fact, your engine has an over-boost protection mode and guess how the engineers decided to protect your engine from too much boost pressure. Yes, thats right - reduce the fuel flow which in turn will slow down the turbo (ie less heat) and reduce critical boost pressures.

So my recommendation is - before you decide to replace your turbo learn as much as you can about the critical aspects of fuel delivery and ignition in your engine. First do a compression test. Then move to fuel flow ( ie all filter include tank filter new), fuel tank properly venting, new air filter, correct injection timing, proper spray pattern and balance of your injector nozzles, proper operation of your overboost circuit, and unrestricted exhaust system.

1987 300D Turbo Charger pressure

Kent,
Thank you very much for your advise. I saw in the manual diagram that the overboost protection was linked to the fuel pressure. I will do exactly what you said and start with the comp test.(providing the compression is good) I bought new injectors from you a while ago so I will install them and change all the filters.
Does the overboost pressure switch ever go bad? Is there a way of bypasssing it to check the switch?

Thanks Art D

1987 300D Turbo Charger pressure

Oh also I forgot to include this information. I have been running this car on 100% Bio-Diesel with the exception of December - March on ran it on about 50/50 mix. The power has remained the same on both fuel mixtures.

Thanks Art D

1987 300D Turbo Charger pressure

Kent,
I didn't realize that most of my questions were addressed in your Diesel Performance Tuning and Repair Manual. I bought it last year and read it today. I have your injector tester coming in tomorrrow along with the shim kit.
I changed all the fuel filters and air filter (no power change)
Tomorrow I am going to check the timing chain, valves, and do a compression test.
I am going to change the injectors, Test,shim, and balance the new ones.
The ALDA unit on my 87' Doesn't have the banjo line running to it. It just has 1 vacuum line. Its tucked under the intake manifold. Can this be adjust similair to the 617 ALDA?

1987 300D Turbo Charger pressure

Just want to update my progress:
I pulled the injectors and did a compression test. This is what i got: 1)430 psi 2)430 psi 3)400psi 4)400 psi 5)400 psi 6)350 psi.
The old injectors didn't look to bad. I pressure tested them and got: 1)1850psi 2)1650psi 3)1850psi 4)1850psi 5)1700psi 6)1650psi
I put the monark injector nozzles in and balanced them all between 1900-1950psi. I never had any starting or smoking problems before but I wanted to get the best fuel economy and performance so I put the new ones in. It started right up and runs good but I still about the same power and boost pressure.
I think I found the boost problem while doing this job. I checked the overboost pressure switch as outlined in the manual and all checked out good but when I was checking the boost pressure control valve i noticed that the vacuum motor was holding pressure but the actuating rod wasn't moving. It turns out that this turbo has a flap or butterfly valve and its stuck. I won't know if its stuck open/closed or burnt until I get it off.

Good troubleshooting!

Hi Art, great job finding the problem. Let us know if you are able to free up that flap valve. Kent

1987 300D Turbo Charger pressure

Ok, Final and most important posting.
I pulled the turbo and free-ed up the waste gate door. That helped but was not the real problem. I also checked the timing chain and everything was right on the money.
Then after thinking about it for a while I checked the exhaust back pressure. BINGO!! it was 14 psi. I pulled off the cat and it was plugged up badly. Put a new cat on and she is running better than ever. It also cured a very harsh shifting problem I have had from 1st to 2nd.
Now she is pumping out 10psi of boost under load.

Thanks For the help.
Art D