injection pump woes - Mercedes-Benz Forum

 
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post #1 of 4 (permalink) Old 06-20-2006, 11:42 PM Thread Starter
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Date registered: May 2006
Vehicle: 1986 560SEL; 1974 240D
Location: Gainesville
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injection pump woes

Hello friends,

I'm new to the vintage MB scene and I'm already in awe at the durability of these amazing machines. I recently purchased a '74 240d which has been sitting in storage for the past 10 years.

Right now I'm simply trying to get the engine to turn over. I've already replaced the fuel tank, flushed the lines, and replaced the fuel filters. I then primed the system appropriately (using the hand pump and with the top of the fuel filter housing open until it overflowed.)

I traced the problem to the injection pump. Fuel isn't making its way past the injection pump in the nozzles which lead to cylinders #3 and 4. When I crank the engine with the fuel lines between the injectors and the injection pump off, fuel squirts out of the nozzles running to #1 & 2 but not 3 & 4. I took off the brass nozzles on the top of the injection pump for 3 & 4, and cleaned everything up as best I could. Sure enough, the little valves inside the nozzles were stuck. I unstuck them and reattached the nozzles. I tried cranking again, but to no avail. With the nozzles off, I can see fuel filling the chamber inside the injection pump, but they won't squirt fuel out with the nozzles on. 1 & 2 spray fine, but 3 & 4 simply won't pass fuel.

I'm stumped. Is there a clog somewhere? Is the vacuum pressure insufficient to pass fuel through the valves inside the nozzles? What should I do next?

Thank you all in advance for your advice ,

Kevin
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post #2 of 4 (permalink) Old 06-23-2006, 11:28 AM
KCM
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I've never experienced the problem you are having, but I would have to think that it is simply air in the pump chambers of #3 and #4. If you have already took off the nipples and unstuck the valves, I don't know why it should not pump fuel. Was the spring installed on top of the valves? The only advice I have is to connect the injector lines, crack them at the injector, and continue to crank with the foot feed down to bleed out the air. You might try to get the car to start on the two cylinders, then the engine speed might bleed out any air (with the lines cracked open at the injectors). I don't see how the pump could have two chambers/pistions bad, so conclude it must be air.
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post #3 of 4 (permalink) Old 06-24-2006, 12:05 AM Thread Starter
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Well after some head scratching and a consultation of the repair manual, I got the car running late this evening. It turned out that the injection pump pistons inside #3 and #4 were sticking. After some delicate tweaking (read: hitting the tops of the pistons with a rubber mallet), the pistons freed up. I bolted everything together, and she fired right up!

In a totally unrelated topic, I was reading a diesel enthusiast magazine today and they had a feature article on the MB 260D, the earliest production diesel automobile. I think the last production year of that model was in 1938. Anyway, I was amazed at how uncanny the similarities between that early engine and the engine between the wheelwells in my 240D. I was amazed at how so little changed over almost a 40 year time span. I couldn't imagine a 2046 model car to be anything like a 2006 model. But I guess with those old diesel engines, you can't improve on the best

Last edited by kvoviii; 06-24-2006 at 12:39 PM.
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post #4 of 4 (permalink) Old 06-30-2006, 02:07 PM
KCM
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Mercedes tended to do small refinements over time. I would say the biggest change to the diesel engine happened when they changed from pushrods to an overhead cam, I believe in the late 1950's. The engine didn't drastically change again until 1987. Even the 5 cylinders are just one more cylinder added to the four.
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