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1984 MB 380SL, 1988 MB 560SL, 1983 MB 300CD, 1984 MB 300SD, 1985 MB 300
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126 Posts
Discussion Starter #1
Lately, I have a really bad idle when I start my 83 300D (242,000 miles). The car idles badly when I first start it (rocking back/forward). After about 2 minutes, it smooths somewhat but not like it should. I have checked all glow plugs & they are fine. I have changed both filters. I have replaced the primer pump (thinking I was getting air in the system). I also have used the new primer pump before starting the engine to get out any air in the system (but no improvement). I ran a quart of transmission fluid with a tank of diesel (but no improvement). Lastly, I replaced the rack bolt on the injection pump. Any help appreciated. I am out of ideas! I am thinking I have a bad injector? If so, is there a way they can be tested while in the car?

Richard
 

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1984 300D
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5,070 Posts
You can do the Injector Cutout Test.
Start the Engine and one by one loosen and tighen the Fuel Injection Tubing Nut at the Injectors.
When you loosen the Nut you cut off the Fuel To that cylinder. On a good cylinder doing that should have a very noticable decrease in Enging rpm and it sould run a little rougher.
If the Cylinder is not so good when you cut off the Fuel to it there will little or no change in the Enging RPM or how smooth the Engine is.

The above only tells you which Cylinder is having a problem.
Remove the Injector from the Problem Cylinder and swap it with an Injector from a Good Cylinder.
Do the Injector Cut Out Test on the 2 cylinders you did the swap on. If the Problem followed the Injector from the bad Cylinder it is the Injector.
If the problem stayed in the same Cylinder you have some issue inside of the Engine.

In general somewhere between one hundred thousand to one hundred and twenty Five thousand miles you Injectors are worn and most likely should be rebuilt.

Call around to Diesel Fuel Injection Shops and see what they charge to check the Injectors.

Another think is checking the Glow Plugs with an Ohm Meter is not the definative test. Removing the Glow Plugs and testing the briefly on a Battery is (Pencile type Glow Plugs only).
The Glow Plugs should get hot at the tip first. If the get hot in the center of the element first they are no good.
I had the above happen. The Glow Plug Ohmed out OK but got hot in the wrong place.
Once the Glow Plugs are out the Glow Plug Holes should be reamed or otherwise cleand out of the Carbon buildup.
For more Details:
Repair Links
http://www.peachparts.com/shopforum/forumdisplay.php?f=82

http://www.peachparts.com/Wikka/DoItYourSelf
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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6,561 Posts
Don't forget when you are removing and installing injectors that you need to replace the heat shields too. I've heard that old re-used heat shields can cause smoking problems 'cause they don't seal properly after they've been deformed by their first use.
 

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1984 MB 380SL, 1988 MB 560SL, 1983 MB 300CD, 1984 MB 300SD, 1985 MB 300
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126 Posts
Discussion Starter #5
Valves adjusted 4000 miles ago. I definitely will check each injector. I am leaning against the glow plugs because the engine will rock/roll for about 4 minutes after starting it. I will update when I know more.
 

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1984 300D
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5,070 Posts
Valves adjusted 4000 miles ago. I definitely will check each injector. I am leaning against the glow plugs because the engine will rock/roll for about 4 minutes after starting it. I will update when I know more.
Well, you are close; many have said to ajust the every 5000 miles.
 

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W-1-2-3 Go!
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16,161 Posts
When you replaced the rack dampener at the injection pump did you adjust it properly?

If the bolt is adjusted too tight, it would show symptoms of "loping" or "hunting" idle.

Adjust the bolt when the engine is at operating temp. I don't see it mentioned here but I adjust it with AC running to include AC compressor load.

12mm to adjust the bolt, 14mm to adjust the lock nut. At operating temp w/ AC running, turn the bolt in. The engine should shake at this point. Slowly loosen it until the engine shake or loping is gone. Stop adjusting when the engine smooths out. Use the 12mm to hold the bolt, and use the 14mm to lock it down in place.
 

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1982 300D
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8 Posts
Have you tried running a can of Lubro Moly's Diesel Purge thru it. I take a small clean clear wide mouth bottle like from Gatorade and drill two holes in the lid the size of my fuel lines. I make these holes as a press fit so you can adjust the length the hoses fit into the bottle and they don't come out while running the engine. Then I fill the bottle with the Diesel Purge. Then remove the supply fuel line and replace with a clean clear line and insert it thru one hold of lid so that it stops at the bottom of the bottle. The hose should curl off to the edge which works out good so you can tilt the bottle to get most of the fluid from the bottom of the bottle. Thats why I use the clear hose and bottle so I can watch the fluid level and bubbles in the line. Then I remove the return fuel line where it connects to the hard line. Clean the end of it and insert it 1" or so into second hold in lid. Set bottle next to engine somewhere so its supported. Start engine and run it till the fluid is all gone. During the process I rev the engine up here and there. Some times I even shut it down and let the fluid sit for a while hoping it would clean a little better. As the fluid level gets to the bottom you tilt the bottle so the end of the line stays submerged. Shut it down when you start sucking bubbles. Reconnect lines and enjoy better running engine. Try it you may be surprised how much better you engine will run.
 
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