Leaking Injector Fuel return lines - PeachParts Mercedes-Benz Forum

Beastie · #1 09-15-2010, 01:26 PM

Hi, I just replaced all the under the hood fuel lines and am about to do the newer Bosch primer change over. I replaced the injector fuel return lines a couple of nights ago and have driven it a few times since. The mileage appears down somewhat but I was not concerned since my next job is to replace the glow plugs and later in the winter new injector nozzles ( if a Diesel Purge does not do the trick). After I popped the hood this a.m. I smelled fuel stronger than usual and looked under the car to see a nice puddle at a fairly strong rate.
Backtracking I looked at the return lines and saw the last 2 were leaking at a visible rate. I was fortunate enough and lazy enough that I left my 2x3 steel drainge sheet pan beneath the car over the last few nights or I would have a gapping hole in my asphalt driveway.
I ran the engine around town and on the highway after I replaced the return lines and happily found no drips no runs no errors. As a side note I changed the lines to VITON.
Now the last few evenings the temp here has dropped into the 55-65 degree range so my first thought was how that would effect the fuel system.
I cleaned up around the still connected fuel lines with electromotive cleaner and used compressor air to dry. The fuel was still weeping at a good rate even though I had tried to reseat the hose ends.
The car is sitting in full sun and it is now almost 80 degrees out. I popped open the fuel tank cap and WHOOOOOOSH!!!
Now the fuel has stopped. I recut new Viton hoses and made them a little longer in case being to short it had pulled the contact between the steel injector nipple and the hose. I have not gotten under the car yet to do the tank lines as well as the strainer etc but does it seem possible that the tank vent is clogged and that the temp change was preventing the fuel from returning and in fact the temp increase raised the return line pressure just enough to make the 2 most poorly seated leak ???
Where exactly is the tank vent and thoughts on clearing out debris that may be blocking it ????? I am going back out to do the primer pump and clean/service the Alda system so I will check this thread again in about an hour.
Thanks
Alan

Cr from Texas · #2 09-15-2010, 01:58 PM

Did you make the classic mistake of cutting of the old lines and damaging the nipples?

toomany MBZ · #3 09-15-2010, 05:02 PM

Check here for a pic from below: 1982 300sd starving for fuel

The file from the FSM is too large to post, but it's a vent, it shouldn't make as much noise as you state.

Diesel911 · #4 09-15-2010, 07:02 PM

Take an extremely close look at the area where the Nipples come out of the Injectors. They are sort of crimpped or swedged in with a circular Crimp.
It does not happen often; and even less so for 2 of them to leak because the Nipples are loose in their seat in the top of the Injector Body.
Raplacement uf the Upper Injector Body is the Normal fix for that.

Using a Socket that contacts the Nipples when you use it can cause loose Nipples; dinged up and bent Nipples.

Beastie · #5 09-15-2010, 08:52 PM

I cut 2 new pieces after I read some threads about the usable bending radius of the VITON being less than the original hoses. I made them slightly longer and reinstalled. Went ahead and did the new style primer pump install and cleaned/serviced the ALDA line/ switchover valve and cleaned the banjo bolt at the intake manifold. Ran the car and again checked for leaks. So far nothing but I will check again in the a.m. and post. Thanks for the input these may be the next step I went to the easy steps first.
Alan

Beastie · #6 09-15-2010, 08:57 PM

Bob, I just used the link. It sounds like what I have experienced. I have still not
cleaned the tank strainer screen but when the tank gets low it does the same starving for fuel/power. Fill up and smooth sailing. I will clean out the bell somehow ( coat hanger) and update.
Again thanks
Alan

toomany MBZ · #7 09-16-2010, 08:17 AM

How is the primary filter? Does it seem to get a bunch of junk in it quickly?

There be enough critters in your tank, when the fuel gets low (separate from a clogged vent) they may clog up the tank strainer.

vstech · #8 09-16-2010, 09:46 AM

did it whoosh air into the tank or out of it?
the tank vent only lets air in, not out. you DO NOT WANT VACUUM in a diesel fuel tank!!!
cleaning the vent will not hurt,but it will not let air out of the tank! likely you did work with the tank open to atmosphere when it was cold out, then when it warmed up, the nearly empty tank, had excess air pressure in it. if you have any tiny leaks air will push fuel out them!

tangofox007 · #9 09-16-2010, 03:39 PM

Quote:

Originally Posted by vstech

the tank vent only lets air in, not out.

Do you have a reliable reference for that? Or are you just speculating?

Do we even know what vehicle is being discussed? Putting together a few pieces of the puzzle suggests a W126, perhaps. If that is the case, the 617.95 engine manual states that the fuel tank vent relieves both positive and negative pressure (to the extent that either exceed specific thresholds), as it well should.

Additionally, the fuel cap is designed to relieve positive pressure above a 0.1-0.3 bar level.

Beastie · #10 09-16-2010, 07:15 PM

Tangofox007, Right ! I did forget to post what vehicle, I was doing a lot of posts and got wrapped up. Anyway I believe that it was my lack of experience with Viton hose and how the difference that makes it less susceptible to interior decay from various fuels also reduces how it's functional flexibility is also
reduced. After redoing the 2 lines leaking and driving to bring everything up to temp the leaks did not reappear. We actualy had a greater temp difference today then yesterday and still no leaks. I will watch it but I believe it is resolved. Of course my asphalt drive suffered some but ????
Bob, Thanks for the vent location. Since the car sat for awhile I am still going to clear the vent. Thanks everyone, as always great input and good for future reference.
Alan

mach0415 · #11 09-18-2010, 05:53 AM

From time to time, my fuel tank holds vacuum. When I fill up I hear the same swooshing sound and it is ingesting air, not exhausting it. Why is that bad? Is it making the lift pump and IP work harder?

vstech · #12 09-18-2010, 09:05 AM

if your cap inhales when you pull it off, open your trunk and pull the tank shield out and inspect your fuel tank. if it's crinkled, it's run with vacuum too long and atmospheric pressure has crunched the tank. if it looks normal, likely it's just mild temp differences in the air in the tank, and not a problem.

bobodaclown · #13 09-18-2010, 09:42 AM

Quote:

Originally Posted by mach0415

From time to time, my fuel tank holds vacuum. When I fill up I hear the same swooshing sound and it is ingesting air, not exhausting it. Why is that bad? Is it making the lift pump and IP work harder?

Attached is the Function of Fuel Tank Ventilation from the service manual.