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  #1  
Old 09-21-2009, 04:30 PM
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Fuel Pump Replacement

I have a 1984 300SD. Lately I have noticed that the engine runs very roughly on startup, and then smoothes out after it has been running about 10 mins. A mechanic friend says that it is the fuel pump, and that it may need to be rebuilt. I was just wondering what else I may consider?

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1984 300 SD running SVO
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  #2  
Old 09-21-2009, 09:20 PM
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If it was the Fuel Pump not putting out enough Fuel I would not expect it to get better with 10 minutes use.
However, if you have the Old Style Hand Primer with the shiny Aluminum body they can become the source of air leaks when they get older; as can the old Fuel Inlet Hoses.

While the above is worth looking into first; 10 minutes seems like a long time to restore the prime if you have an air leak.
It sounds to me more like when your Engine finally gets up to operating temperature it smoothes out.
That is an indication of something going on in the Precombustion/combustion chamber and the Fuel is not burning well until the Engine gets hot.
I would first check to see if all of your Glow Plugs are working.
If they are OK I would be thinking to do a Compression Check on the Engine or have the Fuel Injectors checked or Rebuilt.

But, we could use more information.
Are you using only Diesel fuel?
Are you also having hard starting?
During that 10 minutes when it is running bad is there any smoke; and if so what color is the smoke?
When the Car is running OK and on the Road is there any smoke ;and if so what is the color?

If you have not done a Vlave adjustment for a long time some members have said it helped smooth their Engine out and helped their starting.
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Old 09-21-2009, 09:48 PM
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I forgot one. How high is your idle speed set to?

Some folks set the idle speed to low to save Fuel.
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Old 09-22-2009, 09:23 AM
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The car was modified to run on SVO which means it has two fuel tanks. The main tank can hold SVO or Petroleum and the fuel line has a Racor Marine Fuel Filter. For the last year I have been using petroleum almost exclusively. I was thinking maybe the Racor filter should be changed. However, I suppose it can be tested by running on the Diesel only tank which has the standard fuel filters on it. I should note that the main tank is heated by a radiator that is feed from the coolant system. Surprisingly enough that heater heats up after ten minutes which means the fuel is warmer by then and the engine settles down. I am not sure what the color of the exhaust is at start up, but I believe when I am on the road there isn't any smoke. I suppose white means I have a moisture problem and black means I have an incomplete burn happening. I did see strangely enough that there is rust collecting on the fuel cap, and I am concerned about moisture in the main tank. I am not sure what the idle speed is. How can I check? Since I live in New York City, I don't drive the car everyday which means she may sit for two or three weeks unused. I changed the glowplugs about three years ago, and the car does start easily, but just runs roughly.
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Old 09-22-2009, 09:37 AM
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Wait...I'm confused. You say you can put SVO or petroleum in the MAIN tank? I'm assuming the MAIN tank is the STOCK tank? If you put SVO in the STOCK tank you are cold starting on vegetable oil. Not a good thing. Even though you haven't used SVO in awhile, this may have done some damage to the injectors. Only use the SVO AFTER the engine is up to operating temperature via the 2nd tank and properly purge.

I highly doubt it is the fuel pump. The pumps on these cars are incredibly tough.

Idle speed means what RPMs is the engine running at when it is idling.

I would check the valve clearances, motor mounts, and suspect worn injectors.

I think we need a little more clarification on your SVO system to really understand and help your issue.
Where is the 2nd tank? Are there any heaters on the 2nd tank?
Describe the mods to the main tank.
Describe all mods made.
Describe the fuel selection when running SVO.
Describe your SVO source/filtration process.
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1985 300CD
1981 300TD


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1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD
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  #6  
Old 09-22-2009, 10:12 AM
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I never start the engine on SVO. When the main original tank has SVO I start on the adjunct tank. However, in the last two year I have used SVO only once.

At this point I am using only Diesel since SVO is hard to come by these days.

The car starts easily but idles roughly.

The car has a second tank which only takes Diesel and is not heated.

The only modifications are two accomodate SVO which includes:
  1. New 6 gal unheated tank that only takes Diesel
  2. New fuel line to old tank that is heated by close contact to two cooling system hose lines
  3. Cooling system has new hoses that go alongside new fuel line to old tank and goes to a radiator in old tank
  4. Old fuel line redirected to new tank
  5. New fuel line is filtered using Racor Marine Filter
  6. Switch attached to solenoid to change which fuel line to use

There is a known problem that sometimes air gets into the fuel system, and the guys who installed the system put a bleeder valve on where you can manually bleed the system of air. This needs to be done rarely.

The engine always is started on cold Diesel fuel

Is valve adjustment done on the IP?

I had been buying new oil and very rarely using filtered waste oil, but with the rise in food oil and crisis in third world food supply, and competition for waste oil in NYC, I have been using Diesel exclusively the past few years.

I have to check the microns on my waste oil filtering bag.

Thanks for your help too. I hope this has been clear.
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  #7  
Old 09-22-2009, 10:49 AM
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Yes that helps. Were you purging the engine of SVO (when you were running SVO) before shutdown? Approximately how many gallons/miles on SVO? Doesn't sound like yo'r problems are related to SVO/WVO.

A valve adjustment is done by taking of the valve cover (on top of the engine). See here- http://www.dieselgiant.com/valveadjustment.htm

Describe the rough idle. These cars tend to shake a bit no matter what. There is another thread right now with the person experiencing a 'rough' idle. You may want to check it out.

To reduce the shaking as much as possible (but probably not eliminate it alltogether), the following things can be done-

Rebuilt injectors
Motor mounts
Valve adjustment

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2009 ML320 Bluetec
1985 300CD
1981 300TD


Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD
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