Before you go any further be sure that it is not the pipe connection that is leaking.



On the Bosch MW pump fitted to your model there are only two other possible sources of a leak.

1) The copper washer between the delivery valve and the metering element.
2) The lapped faces that “wring” together between the del. valve body and the pipe conn./spring housing.
Both of these must seal a pressure of <1800psi.

Sometimes you can be lucky if you do not disturb the del. valve body and it will not leak but if it does as in your case then the copper washer must be replaced and thoroughly cleaned out.

The del. valve body is best lifted out with a magnet, you can also use a thin wire and hook it out from under – Keep away from the chamfer where it seals, new D valves are expensive!

You will have to get a new copper washer from a Bosch agent – 15mm x 10mm x 0.5mm thick, don’t use a substitute.

The faces of the del. valve and the pipe conn. can be cleaned using a piece plain paper on plate glass with silver polish. Don’t even THINK about using abrasive paper!

To re-assemble: Tighten to 30Nm and release. Again to 30Nm and release then finally to 48Nm. The purpose of this is to ensure the lapped faces are seated squarely and wrung together before final tightening. Always use two wrenches when tightening inj. pipe nut.

BTW - The thread is parallel not tapered and there are no “O’ rings in the MW pump del. valve assy.


__________________
Beagle

The leak is at the base of the pipe where it screws into the metering element. I had previously thought that the pipe had to seal with the metering element, but from what you have said (if I understand), the high pressure fuel is sealed in the stack of parts in this order: injector pump body, copper seal, pressure valve carrier, pipe connection. There should be no fuel running around this stack and no need for a high pressure seal on the threads of the pipe. The only two places it could be leaking are the copper seal or the lapped faces of the pipe and the pressure valve carrier. Do I have it right?




I'll try my local Benz dealer for the copper seals. Anybody know a Bosch shop in south Atlanta or the best mail-order Bosch shop? Thanks.

This IP came with a factory rebuilt engine and has 100,000 miles on it. No dirt on it inside or out. Since the leak, it's running rough and nailing on number 1, so I guess it's not getting high enough pressure to actuate the injector properly.