FuelFlow Questions for OM606 and Starter/Battery Saver Tips

[anghrist]

Okay folks. I've been thinking about this for a while and it's really bugging me. The OM606 fuel flow pattern is as one person put it "absurd". From a flow dynamics standpoint, a fluid pump will always push better than it pulls. This would indicate that the W210 chassis diesel would have benefited greatly from a fuel pump either in or under the fuel tank; however the geniuses in charge of the design of the fuel system on this car saw fit to install a mechanical "lift" pump on the engine instead... 1960s GM Tech anyone?

Sorry, I'm just getting gripey after chasing more air leaks in the lines. My real point is this. The lift pump is basically siphoning fuel from the tank. Any air leaks in between the tank and the lift pump can show up in the clear plastic lines (we all should know this by now). However there is another effect that I hope to make a recording of this weekend. What can not be observed with the OM606 engine is that, given the right conditions, there will be a bubble that remains in the prefilter. I, tried replacing the stock prefilter setup with a clear 1977 style prefilter to show that this is the case. This bubble does not dissappear, and will remain in the prefilter. This is where the "shutdown" bubble comes from in the prefilter/thermostat/fuel heater line.

This bubble is common in a siphon environment. Anyone who has conducted a diesel purge using clear tubing can see the effect readily. When this bubble exists and throttle is applied the lift pump can generate enough suction to pull this bubble down trough the prefilter and into the rest of the system. Typically this would not be a problem, the air would be purged in short time and there would no longer be a bubble in the prefilter right?

So why would the bubble come back at shutdown. Answer: there's always a bubble in there (leaks or no). The only way to totally eliminate the bubble would be to positively pressurize the line from the fuel tank. I'm looking into a fix for this that will properly work with the Mercedes system.

Sorry folks, I'm just thinking and typing about this to see if anyone else has any ideas. Now on to the tips

**Starter/Battery Saver tip**

After performing any maintenance on the fuel system in which fuel lines had to be removed follow the following steps:

1) Open hood and make sure all lines are connected correctly (obviously)

2) Remove line from top of prefilter.

3) Turn key to preglow position (opens shut-off valve)

4) Using a can of Diesel Purge, and a turkey baster prime system (fill baster and squeeze diesel purge into the prefilter, make sure you shove the baster in there tightly otherwise this will get messy)

5) Prime until Diesel Purge tries to spray out of prefilter (it will)

6) Replace line to top of prefilter and bolt in place.

7) Re-glow and start.

Gosh that's much nicer than grinding on the starter for minutes at a time.