Hello, working on a 1996 E300 W210 606.912

Have had a problem with the car for a couple of months now that started with it shutting down after long trips. I posted about it when I was traveling and was stuck out of town and saw bubbles in the lines. I installed an electric pump in-line at the firewall and it drove great for the 6 hour trip home.

Since then all of the clear lines have been replaced and the shut-off o-ring and the banjo bolt o-ring and crush washers, but still a stream of small bubbles from the banjo bolt return line from the right side of the IP and from the return line from the shut off valve. Have replaced the o-ring and crush washers there 3 times and then suddenly yesterday a leak appeared from the gasket on the back of the IP and it is a bad one, very steady flow while just running the electric pump to prime before starting the engine.

What can be leaking from internal Injection Pump?

Notice the drip of fuel just above the paper towel at the gasket at the rear end of the IP.

Thanks for reading.

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I'd be inclined to think the shaft seal on the lift pump is roached (easy fix). It's about the only thing other than a catastrophic failure internal to the pump that's going to leak fuel into the oil side of the pump. Fix this ASAP since you're dumping diesel into your crankcase oil and diluting it. You'll wreck your engine if you keep dumping fuel in the crankcase.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

So its this then. Bubbles are coming from there and it leaks down as well.

I see that some rebuild and some think that its not worth the risk of rebuilding a $150 part.

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The shaft seal is easy to replace on these pumps. A few cents at a hardware store for a new one. The 606 is an evolution of the 601/2/3 design. See the picture below for an exploded diagram:

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

now we will be on the road and have a project

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Replaced lift pump.

The leak that I thought was from the gasket at the back of the pump was in fact from a pinhole in the fuel line, from the banjo bolt to the filter housing, that was spraying onto the IP and dripping down the back side.

So I re-replaced the line and the two crush washers and o-ring.
Also replaced the banjo bolt on the return line to the filter housing ($50).
The new banjo bolt made it all go back together just right the first time.

The car runs good and idles smooth but when given throttle air can be seen in the line from the left of lift pump to the bottom of the shut off valve and the line from aft (right side) of the shut off valve to the fuel filter housing.

Chasing bubbles for weeks now and am about ready to re assemble the engine and live with the small amount of air that is in the lines but at the same time after all of this time it should be right.

How much air is acceptable?

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