Date registered: Mar 2006
Vehicle: 2006 E320 CDI, 2009 ML320 Bluetec, 2009 GL320 Bluetec
Location: Boise ID
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2009 ML320 Bluetec Boost pump underpressure
2009 ML320 Bluetec Prdouction date May 2009
The in tank boost pump appears to have a defect and not limited to one vehicle. On our recent trip from Chicago we had it drop off line.
What to look for:
-Greatly reduced power
-Missing, jerking stumbling at low rpms
-Stalling (at low rpms)
The reason is the boost pump in the tank provides head pressure to the high pressure pump. Without this pressure the high pressure pump is unable to suction feed the fuel from the tank thru the fuel filter and still maintain sufficient flow to pressurize the rails. The result is a loss of power regardless of throttle input, hesitation due to low rail pressure, restricted flow to the high pressure pump due to the systems filter and distance the fuel must travel from the tank.
NO CODES WILL BE STORED OR TRIGGERED WHEN THE PUMP DROPS OFF LINE! There will be no indications to the driver other than the drivability of the vehicle.
The vehicle may stall (and ours did twice) without notice.
The issue is intermittent, it will drop off line for a period of time and then operates normally and full power returns.
It appears that even when the pump is operating normally, the actual boost pressure to the high pressure pump is under-performing (below min specification) by about 20%.
My advice isthis, if you suspect you are having issues with the tank boost pump, keep the fuel level topped off. This will increase the flow rate to the engine and reduce the chances of drivability issues. Do not let the tank drop below 1/2 since the issues appeard at about 3/8 tank.
No drop in fuel economy was noted.
Last edited by drivbiwire; 08-20-2009 at 01:50 PM.