I've been trying to narrow down the cause of my sluggish 606. I wanted to eliminate a clogged fuel supply as a source so I filled a 2 quart container with fresh diesel and put the supply hose deep in it. I plugged the hard line coming from the tank so I wouldn't get diesel all over the place. I did not put the return line in the 2 quart container. I went for a spin and got about three blocks. Car died. I looked and the fuel supply was empty! Is there really that much fuel sent through the pump that quickly? I'm guessing that I would have been okay if I would have put the return line in the 2 quart container, but I'm not sure. that's a lot of fuel in a few blocks. I wasn't gunning it either.

Finally I switched supply and return hoses where the fuel lines enter the engine compartment and went for a spin. No difference.

__________________
2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900

Yeah, the pump moves a lot of fuel through it and only a portion is actually diverted to the engine to burn. I think it's about a half a teaspoon every cycle of the lift pump.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

That is correct, the return hose is just as critical as the supply hose in a Diesel engine. The returned fuel is used to cool the injector tips and provide lubrication to the pump. If you have ever grabbed a return line on a just shut down engine you will understand, that fuel is quite warm.

__________________
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