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Old 11-05-2003, 09:30 AM
Michael Stoic Michael Stoic is offline
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Join Date: Apr 2003
Location: Boston, MA - USA
Posts: 17
Thank you, Deanyel and Cap'n

Today was a cold morning and the motor stumbled through the cold start. It caught in a lumpy sort-of way, in about 4-5 seconds of cranking, but evened out to the high warm up idle speed without problems.

Still, the lumpy cold start behaviour is a relatively new development, and now that I think about it, the car began to gradually develop that condition over the last few months. I originally thought: "plugs, cap, rotor."

I guess the progressively lumpier starts condition coincides with the progressively failing Fuel Pressure Regulator.

Aside from this, I am curious about one more thing - the vacuum line from the FPR and the diaphragm it controls: I've read posts where people say the vaccum line is merely a vent. From my limited knowledge of MB Fuel systems, I would have concluded that the vaccum line controls a diaphragm, under which a spring mounted valve of some sort operates inside the FPR.

One thing is clear - fuel should not make its way into that vaccum line, but if it does, the FPR is failing (or failed) and the fuel might end up in the crankcase.

Finally, I am wondering if a high Fuel Tank pressure (you know - a nice big pressure puff when the gas cap is removed) can cause or contribute to the failed diapragm in the FPR.
Michael Stoic

1979 450SLC
1989 300SE
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