2005 E320CDI fuel return line pressure - PeachParts Mercedes-Benz Forum

spark3542 · #1 09-25-2015, 03:00 PM

I've searched and haven't found a similar problem, so I'm posting new.

My 2005 E320CDI experienced a fuel leak last week. Difficult to see initially, due to all the plastic shields underneath the car holding the fuel and letting it go at various times and from various spots.

I determined that the return line hose came loose from the barb on the #2 injector. The fuel collects in the injector area, and routes it to the rear of the engine, then drops it onto the bellhousing/starter area.

Assuming the return hoses may be tired after 257K, I replaced all the short injector return lines with MB dealer hose.

A short test drive showed success. An extended test drive had fuel leaking again. I found one of the new injector return lines came loose at an injector.

I'm assuming that the injector lines are seeing excessive pressure, especially since these are designed with no clamps, just hose pushed over a barb.

The return line to the tank collects fuel from three places...injectors, back of the fuel rail, and from the HP pump as well. Breaking the circuits shows no excessive pressure or flow from either injectors or back of fuel rail. The line from the HP pump has significant flow. I attached a pressure gauge and read about 7psi with all lines connected.

Is 7psi correct? Would that indicate some blockage in the return line between there and the tank? I blew the line with compressed air from engine area to tank, and it seems clear, but any details or info is welcome please.

Thanks

barry12345 · #2 09-25-2015, 04:07 PM

Well seven pounds should not be pushing the hose off. Try a small clamp. If it is a real overpressure situation the hose will then pop off somewhere else. Then a more serious look is needed . Also have a look to make sure the barb looks good.

Although I guess the pressure would elevate as revolutions increase if indeed there is a restriction further back in the return line. Or the line itself is too restrictive in size for the input flow it will build further pressure.

spark3542 · #3 09-25-2015, 05:27 PM

The barbs look good, and it was actually a different barb from the first time to the second time. Both on injector 2, but the first time was between 2 and 3, and the second time between 2 and 1.

spark3542 · #4 10-21-2015, 05:56 PM

Update,
Yet again a new piece of return line came off the injector hose barb. I did several miles of test driving with fuel pressure gauge connected inline with return line. I never saw the pressure go above 7. (Some of this test driving was during the SBC brakes red-dash-of-death issue...see my other thread on that).

I found another thread about replacing return lines with PFA Teflon tubing. I procured all the tubing and clamps per that thread, and have had no fuel leaks since. That tubing is rated for a wide range of temps, and a wide range of chemicals. About 1000 miles on new return lines now.

The thread was from a different forum. Here's the link if the moderators will allow it: http://www.benzworld.org/forums/w211-e-class/2036961-e320-cdi-return-fuel-line-replacement.html

Josh8loop · #5 05-20-2016, 08:42 PM

Quote:

Originally Posted by spark3542

Update,
Yet again a new piece of return line came off the injector hose barb. I did several miles of test driving with fuel pressure gauge connected inline with return line. I never saw the pressure go above 7. (Some of this test driving was during the SBC brakes red-dash-of-death issue...see my other thread on that).

I found another thread about replacing return lines with PFA Teflon tubing. I procured all the tubing and clamps per that thread, and have had no fuel leaks since. That tubing is rated for a wide range of temps, and a wide range of chemicals. About 1000 miles on new return lines now.

The thread was from a different forum. Here's the link if the moderators will allow it: E320 CDI return fuel line replacement with Teflon Tubing - Mercedes-Benz Forum

How cool, someone took the plunge and followed my lead. My Teflon return tubes have been working flawlessly for quite a while now. Really I need to get some more of that tubing and replace all of it that goes from the #6 injector down to the banjo fitting. That way at least that would be sorted out too. Glad to see it worked out for you also. In addition, your return fuel pressure question...I have tested my return fuel pressure and have measured 15 psi with a calibrated gage. I wonder if mine is a bit on the high side then?

spark3542 · #6 05-23-2016, 09:37 AM

Josh8loop,
Thanks for your original post. I have 272k now and the return lines still look great!

I haven't measured return line pressure since my issue, Mine never went above about 7 during that time.