The car sat for two years with the hard metal lines removed. The system primed easily enough, but line #3 has a terrible amount of air coming through it even after the engine has run for a good while. When the fitting is cracked open there's an enormous quantity of foam spewing from the line. None of the other cylinders exhibit this behavior. It seems this would be an internal issue with the pump. Any suggestions?

If it was sitting exposed, my guess is that element is toast. Either rebuild or good used pump.

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

The delivery valve could be held open by a chunk of dirt, allowing fuel to push/pull instead of just pushing out. I'd take it apart and have a look. Might be as simple as cleaning it up and putting it back together with a fresh o-ring and crush washer.

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- Greg -
1973 220D, The Prodigal Benz
1974 240D

I was hoping that was a good possibility. I'll check that out tomorrow. I'm glad I have a few extra o-rings and new washers around. 👍🏻

I'm hoping that it's not that drastic. I sure hope not, but that's a real possibility.

Probably dirt or rust inside

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

If it sat open and exposed to the air for years then I'd suspect the delivery valve as the most likely culprit. Probably dried out and formed a ring of rust and/or sediment that's preventing it from seating. Pull the #3 DV holder and pull the DV and take a look. If that's all it is, you can probably just polish the seating faces and be back in business.

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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!)

I removed the DV holder to inspect and found there were two crush washers installed at some point. I cleaned the barrel and pintle. I couldn’t really see anything wrong with them. I installed a new washer and O-ring then put it all back together. I fired it up and still had the same air foamed fuel spewing from the line when cracked. I’ll investigate further when I have more time tomorrow. I do believe that it’s a rust/debris issue. I also plan to speak with the local Bosch repair shop and see what light they can shed on the subject. Thanks for the replies and suggestions.

It appears that I solved the issue...just by chance. I decided to hook up my auxiliary tank I use when doing a purge. I filled it with diesel and hooked up the supply and return hoses that are attached to my auxiliary tank and the issue went away. Apparently the supply hose on the car was pulling air. I pulled it off the car and inspected it closely. Sure enough, it was full of hairline cracks. I installed a brand new supply hose and now she’s nice and quiet.