CJ, just curious if you checked the rubber hoses that run in between the injectors. On my 240D, I could smell raw fuel as soon as my wife pulled in the driveway recently, but when I went to look for a leak the next day, I couldn't find one. So I temporarily sprayed a little cheapo paint on all of the fuel lines under the hood & drove the car around town for a while ... came back & I still couldn't find a leak. I drove it on the interstate ... came back & I had VERY small stream of fuel (& cheapo paint - which made the leak obvious) coming from the end of the hose on the #4 injector.

As far as the blue smoke, have you had a thermo recently? If your not burning any oil, then blue smoke is usually a sign of unburned /under-burned fuel ... which would also drop your MPG's. My guess would be the thermo since you don't have any other obvious symptoms.

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1980 Mercedes 240D
1982 Mercedes 300SD
1985 Mercedes 300D
1993 Dodge Cummins Turbo Diesel