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Old 03-11-2000, 04:55 PM
Registered User
Join Date: Sep 1999
Location: Houston, Tx USA
Posts: 12
Hello, I recently purchased an 83 300SD with 276,000 miles. The engine has take off power but the top speed is only about 83 mph. Owning a SD before I know the top speed should be at least 110. Please Help.


1980 300TD 287,000
1983 300SD 266,000
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Old 03-11-2000, 06:17 PM
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Join Date: Feb 2000
Location: Powder Springs, Georgia, USA
Posts: 206
Will it rev up in the low gears? I wonder if it could be something easy like clogged fuel filters or something bad like a goofed up injector pump. Have you changed the filters ?
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Old 03-11-2000, 06:25 PM
Registered User
Join Date: Sep 1999
Location: Houston, Tx USA
Posts: 12
I've changed all the filters including the one in the tank. And I get bad fuel mileage something like 16-18 mpg.

Could it bad injectors?
or worn out engine or turbo?

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Old 03-11-2000, 08:04 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Be sure that the fuel control lever on the injection pump goes to the stop in full throttle.

At 80 you should be into a number of pounds of boost. For proper fuel enrichment to take place the boost signal must get to the aneroid on top of the injection pump. To protect the motor from overboosting there is a switchover valve in the signal hose from the intake to the aneroid. The valve often plugs with soot and can be blown out. Its normal unenergized state is to pass the boost signal through.

Check the boost signal by teeing into the line from the valve to the aneroid. The boost should reach 9-10psi by 2500rpm (my estimated figure) under full throttle. The pressure should drop also as soon as the throttle is released.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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Old 03-11-2000, 08:05 PM
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Join Date: Aug 1999
Location: Cincinnati, Ohio
Posts: 1,935

You could very well be looking at an injection pump rebuild. If it turns out that the pump is the problem, I would recommend you send it to Pacific Fuel Injection in California. I have dealt with them through the shop and they are very good and have very competitive prices. In addition, I would also replace the injectors, rebuilt ones from Mercedes aren't terribly expensive. Since you have had past experience with the 300SD, how does the turbo feel in comparison to your old one? Well, good luck!

Aaron Greenberg
MB technician
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'77 450SL
'80 300SD
'85 380SE
'89 420SEL
'93 300E 2.8
'72 Alfa Romeo 2000GTV
'74 Jensen Interceptor Mk.III
'81 DeLorean DMC12
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Old 03-13-2000, 11:07 PM
Posts: n/a
You have good leads in my opinion. I usually remove the hollow bolt on the manifold that holds the line leading to the switchover and aneroid and give it a good cleaning. If that does not help I temporarily bypass the switchover to determine if that is the problem. Should you decide you need a pump, please e-mail me - we have several from parted-out cars.

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