2009 ML320 Bluetec Boost pump underpressure - Mercedes-Benz Forum

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post #1 of 4 (permalink) Old 08-20-2009, 07:21 AM Thread Starter
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Vehicle: 2006 E320 CDI, 2009 ML320 Bluetec, 2009 GL320 Bluetec
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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 12:50 PM.
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post #2 of 4 (permalink) Old 08-20-2009, 07:51 AM
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First I have heard of this in MB. My Dodge Diesel pickup had issues and recalls to resolve same problem.

1980 450sl traded in
1983 380sec sold
1989 300se traded in
2002 ML320 Gave to Family member
2008 ML320CDI /Full load (inc air susp) minus rear entertainment/ Pewter Silver Black leather
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post #3 of 4 (permalink) Old 08-20-2009, 02:20 PM
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Was discussed here ...

Fuel pump - MBWorld.org Forums

... where it appears a swift "kick" could be a temporary solution!

Kent Christensen
'07 GL320CDI
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post #4 of 4 (permalink) Old 12-25-2013, 09:11 AM
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I just bought my 2008 ML320 CDI and everything was great till two days ago I was driving and the car stalled, I had to put it in park in the middle of the street and finally got it to start but if I gave it more than a slow gas peddle it would stall. I finally made it home and would have to hold my foot on the peddle all the way open to get it to start. I tried to look up what it could be and everything showed a bad fuel filter or pump, so I first changed the fuel filter and it did the same thing stall if you push on the gas peddle How can I change the in tank Pump or should I check for more thing before I change the Pump. I hear the pump running that I never did before HELP!!!!!! I took it to the auto parts store and plugged it into the computer it reads P0087 Fuel Rail / System Pressure - Too Low
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