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Old 12-05-2016, 07:13 AM   #1
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Metal compression fitting

Seems the metal compression fitting for the fuel line under the fuel injector has sprung a leak and there is a small spray of diesel only when the engine is running.

My question is: Can I unscrew this compression fitting and replace it simply? Or, is it under pressure and would I do damage to either myself or the engine?
Or, is this not a simple job and I should call my diesel mechanic?
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Old 12-05-2016, 07:54 AM   #2
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Not familiar with Mercedes engines...but if between the injection pump and injector...best to have a pro at least look at the line if you can remove it easily as it would be a high pressure line.

A close up and overall pic might help diagnose.
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Old 12-05-2016, 08:03 AM   #3
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Yes a pic will help us help you.
Some of those are actually formed into the line.
You might try loosening the fitting, let some fuel dribble out (hopefully cleaning the connection area) and re-tightening. It would be nice to have a torque spec.
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Old 12-05-2016, 08:36 AM   #4
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As noted above you can definitely loosen the compression nut or take the tubing off by loosening both ends as long as the engine isn't running. The nut may be loose or the ferrule or end fitting may have a burr on it that keeps it from sealing. If the latter then you probably need to replace the whole tube as it may be impossible to have it made up locally. It should be a manufacturer's part and hopefully you won't have to buy the whole set of 4, 6, ?, but don't count on it.

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Old 12-05-2016, 09:21 AM   #5
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Yes a pix would help.

However, for the most part compression fittings are not hard to deal with. If replacing, need to know where the fuel line goes and how to replace it. You may have to fabricate a new line, and tie it into the old, which should not be hard, if you have the space. If you have enough line there are simple tools that will create a new ferrule on the end, or if this has one that can be replaced, should not be hard.
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Old 12-05-2016, 11:37 AM   #6
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If it is the steel line that goes from the injection pump to the injector it is under several thousand psi when the engine is running. You can back the nut off half a turn or so start the engine and then shut it off. Tighten the nut back up and see if the leak goes away. Most likely it will still leak meaning that the line is cracked or broken. If that is the case the line will have to be replaced. The lines are not repairable. It can be a major pita to replace these lines depending on engine design. Also, be careful to put all the little clamp blocks back in place when you go back together or the vibration will break more lines later.
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Old 12-05-2016, 12:15 PM   #7
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One thing that may be obvious but was not mentioned, DO NOT touch the fuel spray when the engine is running - it might be of sufficient pressure to inject the fuel into your skin and therefore into your body...

Lots of horrible stories about people putting their fingers over a hydraulic leak and injecting an arm full of hydraulic oil in seconds.
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Old 12-05-2016, 12:45 PM   #8
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Xsbank is quite right. Leave fingers and hands and eyes well away from the spray.
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Old 12-05-2016, 02:21 PM   #9
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Likely the line will have to be replaced. I have done the 'loosen, retighten' with about 25% success. This usually means cracked line or compression nut. They aren't rocket science. You can remove, replace. BUT. Make sure you don't have to move soon. Because the fuel injection pump and lines will need to be purged of air and bled. Not a huge job, but I have yet to find an owners manual that is as good as explaining it as your 'friendly neighborhood mechanic'. I am unfamiliar with your engine. Best as a mech to come do it.
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Old 12-05-2016, 02:50 PM   #10
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The high pressure lines on a fuel injected engine can be pretty special. The fittings may have very particular torque requirements which must be respected. Sometimes the fittings should not be reused (once the threads have been crushed the first time, they won't thread properly again). A future leak could start a fire. As others have said, don't expose your hand, and especially your face, to high pressure fuel (maybe the fitting leaks at 10,000psi but not at 5,000psi. 5,000 psi will cut your finger off, or blind you. Full face shield required). I would either get professional help, or know exactly what I was doing before attempting. Be careful.
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Old 12-05-2016, 02:54 PM   #11
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This job isn't rocket science and anyone with a bit of mechanical aptitude and the right wrenches can do it. It is also good practice for when you run out of fuel and need to bleed the injection system.

Unscrew the nuts at both ends of the tube. Sometimes the injection tubes are ganged together and you have to remove them as a package. So unscrew all of them and remove. Then reinstall with new ones and tighten both ends snugly.

The following is a generic approach to bleeding, but probably will work on all but common rail and DD injection systems. Loosen all of the nuts near the injector about a half turn or so, or if you only changed out one tube, then loosen that one. Then have someone crank the engine while you watch for fuel spurting out at the nut end. Once you see fuel spurting, tighten the nut and watch for the next one. Once you get 3 or so nuts bled and tight, then the engine will probably fire. Tighten the others and you are done. Mop up a few ounces of diesel that will have spilt.

If you are quick with the wrenches the entire procedure will be done in the time it takes to read this.

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Old 12-05-2016, 02:54 PM   #12
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If it won't stop leaking with a little loosen & retightening; take it off, try to match it up at your local junkyard of MB car dealer.
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Old 12-05-2016, 03:07 PM   #13
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There are not too many things I mind smelling like. Diesel fuel is not one of them. Success!
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Old 12-05-2016, 03:11 PM   #14
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Took it down to a custom fitter not too far from me.

Getting it off? Disgusting
Taking a pic? Easy

Paying $75.00 to have one made before the boat parade? Priceless!!!

Who wants to install it? LOL! Kidding

Thanks guys, took all day, but I got it.
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Old 12-05-2016, 03:21 PM   #15
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Way to go!
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Old 12-05-2016, 03:26 PM   #16
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Does it run is the question of the day......
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Old 12-05-2016, 03:27 PM   #17
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I advise you to get new washers for the banjo fitting on the opposite end of the line.
Sometimes old ones seal, sometimes they don't.
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Old 12-05-2016, 03:41 PM   #18
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If you have to reuse the old copper banjo bolt washers, use a propane torch to soften them before replacing the line. Just lay them on a clean metal surface and wave the torch over them. It will turn pink and will be soft enough to deform to the mating surfaces of the banjo bolt and ring.

Cottontop: the pressure inside is likely to be no higher than 2,000 psi. That is still enough to inject diesel through the skin.
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Old 12-05-2016, 04:44 PM   #19
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Make sure you bleed the system after your repair.
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Old 12-05-2016, 05:31 PM   #20
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Breaking a single injector line may not require bleeding....but then if it doesn't want to start.....
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