I just finished a head gasket repair 2 weeks ago and found out today I have a fuel leak. I took the plastic cover off and found that the number 1 injector cavity and #6 injector cavity were full of diesel and the fuel was wicking down the return line which was how I originally found the leak. I cleaned up the fuel, snugged up the fuel line fitting at the top of the injectors and and put it back together without the cover. After running the engine a short time the cavity is filling up with diesel and in both #1 and #6 the fuel is bubbling in the bottom of the cavity. It looks to me like the leak is coming from the bottom of the injector, like air is bubbling up. Could it be coming from the heat seal? I checked the close out photos I took during re-assembly and it shows the heat seal installed correctly. Does that make sense? Do those heat seal leak when installed correctly? One more interesting thing I noticed the fuel intake line coming from the heater and going into the fuel filter is not fully primed, you can clearly see a pocket of air in it. Car starts up just fine.

Most likely places for fuel leaks are the fuel return lines or the mating surface for the 2 injector halves.

__________________
CENSORED due to not family friendly words

Fuel return lines don't like to be reused. Trim 1" and try again. #6 is supposed to have a 1" hose with a plug next to the firewall.

The short line from the fuel thermo to the pre-filter drains back at shutdown, does not mean you have a leaky oring.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

If it turns out the Injector is leaking between the lower and upper halves try pulling the injector and torquing the Nut to the highest limit of the Torque.

On the Older Injectors the little Nipples are pressed into the Injector and a circular crimp is applied over them. Once in a while they leak out fo the crimp.
You either repalce the upper Injector Body with a good one (you need to re-set the opening pressure) or cut the leaking Nipple off and weld over to seak it and transfer that Injector to the end where the Injector with the Plugged line goes.

If you cut the old Fuel Return Lines off it is possible to have nicked the Nipple and that is know to cause leaks and if the wrong Socket is used it can bend the Nipples and make it hard to get the Hose on properly and I guess could also knick them.

__________________
84 300D, 82 Volvo 244Gl Diesel

I had that problem on mine, turned out to be a stress crack in the hard line at the fitting.

The root cause was improper support of the hard lines.

Weepy return lines could be the problem too. Try some weed wacker hose as a temporary fix.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The injectors were pop tested and the tech said they were fine and to not do anything to them.

I used new fuel return lines but will trim the ends and and try again.

When I found the problem, the end return cap/piece of rubber on the #6 injector had blown off the end of the injector and was in the cavity. I re-installed it before the last test and still have diesel leaking with it installed.

Can anybody explain why the bubbling of the diesel in the bottom of the cavity? Would that happen if the leak was at the return line

I was busy today but hope to work on again tomorrow or Tue.

Pop-testing is too short a test to test for the tiny seeping leaks between the upper and lower halves of the Injector and cannot test if the return Fuel Nipples are leaking at all.

If new Heatshields were insalled and they were insalled properly any little leaks should fill in with Carbon after a few 100 miles and seal. In general when there is a good combustion leak in that area any liquid would spray out.

If you get the Fuel Leaking issue solved dry everthing off (you need to reduce this to smaler portions) and spray a mix of 1 gallon of Water to 1 cup of Dawn Dish Soap. That makes a mix that will form bubbles.
Spray that down there and if you have a leak it is going to blow bubbles just like a Kid blowing Bubbles would. But, it needs to be entirly dry when you start and the Engine needs to be cold when you start.

__________________
84 300D, 82 Volvo 244Gl Diesel