Wow, I was leaking diesel fuel from one of the injector bypass hoses last week so I replaced them all. I can't believe what a difference it made. The car idles smooth as glass now, even with the AC on... WOO HOO! I guess it makes sense, leaks equal a loss of fuel pressure.
It only costs about $10.00 for enough good woven Mercedes hose to do all of them so it is definitely worth the effort!

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1982 300D Turbo "Helga"
380,000 miles

BWatson,

Hard to believe. Engine should run the same without those hoses on at all. Are you sure it isn't "sugar pill syndrome"?

There is no fuel pressure on that side of the fuel system. Its just a return of overflow to the fuel tank. My overflow line from the injectors was inadvertantly disconnected when I replace a GP. The 300SD engine ran normal, it just sprayed fuel all over the place.

Any explanations, Anyone?

P E H

Marlene always runs better right after she's been stroked with some new trinket...or at least it seems that way to me. Lately, she's been particularly fond of new Hazet tools...a kinky German broad, isn't she?

Seems to me the only thing those overflows would make a definitive repair on would be crappy fuel mileage.

R

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Never a dull moment at Berry Hill Farm.

It is possible that it's the "sugar pill" syndrome, but it really is idling nice. I'm as suprised as you are but hey...these cars have souls so maybe when they are happy, they let us know. That's why we like them.
My best guess is that it has something to do with equalizing the fuel pressure at low rpms. I noticed that when it was leaking, it would stop when I revved up the motor. All I can figure is that with even the slightest leak, it compromises the fuel distribution. Even a small drop in pressure could account for some rough idling, but here again it still ran fine and smoothed right out at higher rpms. So...The 123 gods are happy today!!!

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1982 300D Turbo "Helga"
380,000 miles

The pressure on that side of the fuel system is whatever pressure is needed to cause the fuel to flow through the lines back to the tank. If the fuel level in the tank is at a lower elevation than the injectors that pressure might actually be a vacuum.

Maybe the leaking lines allow air to get into the injectors. (?)

dculkin,

Ok there is a miniscule amount of pressure in the return fuel lines to overide the friction in the flowing fuel, but air getting into the injectors when there is ~1500 PSI on one side and atmospheric pressure on the other side is impossible. Think about it logiclally.

P E H

P E H,

How about when the engine is off? Could air get sucked in through the injectors? I kind of doubt it unless there is some where for the fuel to flow back through the injection pump and I am guessing that there is a check valve (or something) somewhere to prevent that from happening.

DSC