Changing The Fuel Injector Return Hose On 617 - PeachParts Mercedes-Benz Forum

neversayDIEsel · #1 08-13-2014, 09:00 PM

My braided fuel return hoses that go from my injectors are weeping and leaking so I bought a new roll of housing and plan on reinstalling this week. I was curious if there are any tips on doing this. It seems pretty straight forward but was curious if i should plan on having to purge the system of air with the primer before the car will run again?

Phillytwotank · #2 08-13-2014, 09:06 PM

No purge needed. Just swap and go. Maybe have a needle nose pliers handy to help wriggle the hose off and on the tiny nipples.

charmalu · #3 08-13-2014, 09:13 PM

It`s pretty straight forward. just pull the old one`s off, and push on the new one. Be careful of the nipples if a piece of old hose breaks off. Don`t use a knife, razor blade etc..... to cut the hose. there is a chance of nicking the nipple, and then having a leak.

Just grab the side of the hose with some needle nose pliers and squeeze the rubber and pull off.

No need to bleed the system, these are just the return lines back to the tank.

Charlie

vstech · #4 08-13-2014, 09:39 PM

+1 on carefully removing hose... Grip the hose from the side vertically, and pinch it so it splits off the nipple.

neversayDIEsel · #5 08-13-2014, 09:44 PM

Cool! I need to do the filters too when I have a bit more time as this is my first time purging the system of air. I also read that it's important to dip the ends in diesel to help them slide on.

Out of curiosity, does much fuel actually travel through these? Could their leaking affect engine performance or does it just make a mess.

sleepstar · #6 08-13-2014, 10:05 PM

i dont think it affects performance because the fuel that goes through the lines is unused and going back to the tank. it makes a HUGE mess though. especially at idle.

neversayDIEsel · #7 08-13-2014, 10:07 PM

Makes sense. So everything that's coming back to that banjo fitting on top of the fuel filter housing (the tube from the fuel management system and the braided injector return hose) all travel back to the tank and not back through the fuel filter?

jay_bob · #8 08-13-2014, 10:26 PM

When the injection pump delivers its quantity of fuel to the injector, not all of it goes out the nozzle to be burnt. This is because the spring opens above the set pressure and then closes again. The excess fuel gets pushed into the return line. This also has the added benefit of being a heat sink for the nozzle tip.

Likewise the IP has excess fuel in the rack on every injection cycle, this gets sent back as well.

The two return connections from the IP and injectors join at the filter. The filter also feeds into the return, this is how it rejects trapped air in the system back to the tank.

All of this returned fuel goes through the cigar hose before passing through the steel return line back to the tank. This hose has an engineered cross section that provides a dampening effect on the pulsating return fuel flow. If you did not have the cigar hose, then the steel line back to the tank would vibrate and fail.

tangofox007 · #9 08-13-2014, 11:00 PM

Quote:

Originally Posted by jay_bob

If you did not have the cigar hose, then the steel line back to the tank would vibrate and fail.

If you operate the engine without the cigar hose, vibrations will be the least of your problems.

funola · #10 08-13-2014, 11:08 PM

Quote:

Originally Posted by jay_bob

..... If you did not have the cigar hose, then the steel line back to the tank would vibrate and fail.

Has that happened to you or do you know anyone that it happened to? I find it hard to believe.

sleepstar · #11 08-13-2014, 11:29 PM

i've only read anecdotal stories about people running a straight line in place of the cigar hose and being able to feel/see pulsations.

Jeremy5848 · #12 08-14-2014, 01:34 AM

For those who use biodiesel or a bio/petro diesel blend, the stock hoses are good to at least 20% biodiesel. At 100% the biodiesel will eat the hoses in about a year and you will be back to weeping or worse. In that case, Viton hose is recommended.

J.

Augenblick · #13 08-14-2014, 02:32 AM

Quote:

Originally Posted by sleepstar

i've only read anecdotal stories about people running a straight line in place of the cigar hose and being able to feel/see pulsations.

I ran clear vinyl tubing for a few months on my TD, and it would flop about due to the slack; they're definitely vibration from the pulses, now whether there is enough to damage the hardlines, I'm not sure. I seem to recall there were some euro chassis fitted without the cigarhose, and that you'd get extra cabin vibration, though so much on the wagon was wore out I didn't notice a difference.

sleepstar · #14 08-14-2014, 02:45 AM

Quote:

Originally Posted by Jeremy5848

For those who use biodiesel or a bio/petro diesel blend, the stock hoses are good to at least 20% biodiesel. At 100% the biodiesel will eat the hoses in about a year and you will be back to weeping or worse. In that case, Viton hose is recommended.

J.

this definitely. B100 biodiesel will degrade them into disgusting goop.

Shortsguy1 · #15 08-14-2014, 08:17 AM

My 1968 car was originally manufactured without a cigar hose. At some later time in the w115 run, they introduced it. So someone at MB in the late 60s or early 70s decided it was better with the cigar hose than without, but my car has been driving for 45 years without one and is doing fine. I have tried it both with and without a cigar hose and cannot tell the difference (but my car does not have a particularly smooth idle so it is hard to note subtle vibration/pulsation changes).