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  #1  
Old 11-30-2008, 08:39 PM
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How much air can there be in injection pump?

I have a 1981 300D that is having some air in the fuel lines/injector pump issues.

I ran out of diesel about a week ago and ever since I have been having a very rough running engine.

I bled the injector lines for a while with no results. I had the engine running and I loosened one line at a time.

I then found a leaking fuel line before the plastic fuel filter. I fixed this problem and there is little to no air in that filter now.

I then tried to bleed the injector lines again today. I loosened the nut that holds the injector line to the injector on the front two injectors and nothing but foamy air comes out.

I left them off for almost ten minutes with me increasing RPMs occasionally but they still put out foamy air. Not much diesel at all.

I then loosened one of the back three injector lines and there was a noticeable drop in engine performance.

I think I am running on three cylinders and I don't know how much air the injector pump can have in it. Could I have an air leak somewhere else that only affects the front two injector lines?

Is there something else wrong?

Also, to add insult to injury I cross-threaded the nut on the front injector line and now I presume I need a new line altogether. Anybody have one for sale?
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Old 11-30-2008, 08:40 PM
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there should be none in it.

did you prime it with the hand pump?


check the classified section here on the forum
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Old 11-30-2008, 08:51 PM
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Quote:
Originally Posted by TheDon View Post
there should be none in it.

did you prime it with the hand pump?


check the classified section here on the forum
I think my primer pump is also leaking. I have one on order so if it is I can't get it tracked down yet.

I know that there should be no air in it but there is air in it.

Will loosening the nut and working the primer pump push out air?
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Old 11-30-2008, 08:57 PM
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I would just wait for the new primer pump before trying to go forward. Good chance that is the problem. .
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  #5  
Old 12-01-2008, 01:23 AM
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easy way to find out if your on all 4 or just 3.. crack each line at the injector. See if any of them make no difference in the way the engine runs. Make sure you have fuel out of each line when you crack it. If you have fuel out of each line, but one line makes no difference, try exchanging the injector itself and see if maybe you sucked up a small piece of dirt.
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Old 12-01-2008, 02:13 AM
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Originally Posted by dieselnutnj View Post
easy way to find out if your on all 4 or just 3.. crack each line at the injector. See if any of them make no difference in the way the engine runs. Make sure you have fuel out of each line when you crack it. If you have fuel out of each line, but one line makes no difference, try exchanging the injector itself and see if maybe you sucked up a small piece of dirt.
I have very little fuel from the front two lines.

When I crack them, there is very little performance dropoff at idle.

When I crack one of the back three there is a noticeable change.
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Old 12-01-2008, 09:52 PM
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As a general rule two injection pump elements do not fail at the same time. The common element in your case is fuel or air. Just my opinions of course.

Also when one end of the pump is starving for fuel it does mean something. Now if you had posted it was elements number four and five for instance it would be less certain where the problem is.
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  #8  
Old 12-02-2008, 01:20 AM
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Quote:
Originally Posted by barry123400 View Post
As a general rule two injection pump elements do not fail at the same time. The common element in your case is fuel or air. Just my opinions of course.

Also when one end of the pump is starving for fuel it does mean something. Now if you had posted it was elements number four and five for instance it would be less certain where the problem is.

Maybe his drive way is not level and has an upward grade.
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  #9  
Old 12-02-2008, 01:38 AM
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Originally Posted by Diesel911 View Post
Maybe his drive way is not level and has an upward grade.
It's just I have noticed time after time proper fuel lacking at one or the other end of the pump. I had never considered the pump may not be level with low fuel favoring one end over the other but it does make sense.
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  #10  
Old 12-02-2008, 09:43 AM
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Running out of fuel may have dislodged crud in the tank or somewhere else in your fuel system. You may have a partially plugged tank screen or fuel filter. Also, the bleed hole in the fuel filter head (under the banjo bolt) may be plugged. The MB does a wonderful job of removing air on it's own thru that hole if it's not plugged or if there is not a severe air leak.
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  #11  
Old 12-09-2008, 05:50 AM
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Thanks for the good info.

I have replaced the leaking fuel lines, primer pump and I have tried to bleed all the air from the system.

I have had the engine running and cracked one injector line at a time and left them off for at least four minutes each.

I have removed them all and cranked the engine for about thirty seconds.

I still have not checked/replaced the tank strainer but I will do that tomorrow.

The engine still runs rough.

Where exactly is this bleed hole under the banjo bolt?

How do I unplug it if it's plugged? Can it be done with the filter and lines attached?
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