75 240D fuel line routing - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 12-17-2009, 06:21 AM Thread Starter
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Question 75 240D fuel line routing

Newbie question:
Got a great deal on my son's first car, a 1975 240D that had a single tank WVO conversion installed. To simplify his first car driving experience, I've removed the WVO kit, with the intention of researching pros and cons of 1 vs. 2 tank systems and reinstalling it as a father and son project this summer. This is a lengthy leadup to my real question: What is the original fuel hose routing from tank supply to injection pump, and return line? I've looked all over the internet to find a diagram and can't find one. Short of cornering a fellow 240D owner in a parking lot and asking to look at the engine, I'm hoping someone can give me a verbal sequence or better yet, point me to a schematic diagram. I'm assuming it's Tank > prefilter > lift pump > fuel filter input > fuel filter output > injection pump input. but can't identify the various lines because of the old WVO conversion.

Help?

Thanks
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post #2 of 6 (permalink) Old 12-17-2009, 09:32 AM
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The routing you describe is correct.

The return line runs from the fuel filter (where the return lines from the injectors and the pump come together) back to the tank.

I'm afraid I cannot help you with a diagram.
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post #3 of 6 (permalink) Old 12-19-2009, 11:21 AM Thread Starter
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Got it - Thanks

Thanks for the confirmation, motor runs fine except for a slight misfire at low idle. Subsides as rpms increase (or is not as noticeable) Thinking it might be a gummed up injector.

To isolate which one, the recomended diagnostic for my VW 1.6D is to breifly loosen up the injector / pipe nut while running at the suspect cylinder to see if it changes the idle characteristics. Any downside to this technique on a MB?
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post #4 of 6 (permalink) Old 12-20-2009, 03:21 PM
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No downside, you can do that.

However, the proper method is taking the injectors out and have them tested for opening pressure, spray pattern and leakage.
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post #5 of 6 (permalink) Old 12-20-2009, 05:40 PM
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Originally Posted by hjackson View Post
Thanks for the confirmation, motor runs fine except for a slight misfire at low idle. Subsides as rpms increase (or is not as noticeable) Thinking it might be a gummed up injector.

To isolate which one, the recomended diagnostic for my VW 1.6D is to breifly loosen up the injector / pipe nut while running at the suspect cylinder to see if it changes the idle characteristics. Any downside to this technique on a MB?
By the fact that the car had a WVO kit means that your injectors are probably coated in glycerin residues. If you sequentially disable the injectors you may be able to isolate one if that is in fact the case but it is likely that all four injectors will need rebuilding to optimize the pop pressure and spray pattern.

1977 - W116 - 6.9
1974 - W115 - 240D /8 - 4(M) OM617.910 + Turbo + 300D FW - Completed 7/8/10
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post #6 of 6 (permalink) Old 12-20-2009, 09:12 PM Thread Starter
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Thanks again

Excellent advice. I'll pull the injectors and have them tested.

The car died on me today after running fine for 2 hours on the freeway, got it going again by pumping the primer a bunch of times, but don't trust the car at this point to hand over to a young driver.

Besides the injectors, I suspect air is getting into the system somehow or fuel flow is restricted. Will check all of the hose connections. Will also change primary and secondary fuel filters.

Any other possiblities?
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