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ML350 Idle Misfire Cyl. 6

Old 01-11-2019, 03:47 PM
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W163 ML350 2004
ML350 Idle Misfire Cyl. 6

Hello all, I am new here and my English is not very good.
I bought a ML350 W163 MY2004 with the following problem.
When I start the car it starts good, and stays like that for few seconds as long as the RPM is above 1000.
After that the RPM drops and the car start to misfire and the Idle becomes rough.
I have an OBD2 Adapter and the only error code is P0306.
The car has a LPG system and it misfires on Idle in Gas and/or Petrol Mode.
After some time the ECU turns off the 6th cylinder.
When I start the car and drive immediately I get no misfire until I stop (Traffic Light or so) and the RPM drops.
The parts/ Tests I already changed or made:
-Spark Plug (Swap).
-Coil Wire (Swap).
-Coil (Swap).
-Petrol Injector (Swap).
-Mass Air Flow Sensor (Original New).
-Cylinder 6 Compression Test (Dry): 150 psi and is in the same range as other cylinders.
-Cylinder 6 Leak Down Test: about 10%.
-Spark Signal Test with Multimeter and Oscilloscope: Signal is good and is equal to the other cylinders.
-ECU Visual inspection and ECU spark Transistor (FETs) test and they are all OK with the same values and there are no breaks in the board.
-Left side Cat loosening: made no difference.
Now can someone help me to pinpoint the problem?
I have doubts about the Exhaust Valve in the Cylinder 6.. Could be there any other possibilities or tests that I should do? Is there any test to make sure that the problem cause is the Cylinder 6 Exhaust Valve?
Thanks in advance.

Last edited by abodah; 01-11-2019 at 04:19 PM.
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Old 01-11-2019, 04:17 PM
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W163 ML350 2004
Things I forgot to mention.
-Removal of valve cover and the valve spring is not broken.
-When I turn off the car I see and hear air bubbles up the reservoir but the car does not over heat nor lose coolant.
-Battery voltage is 14.3 when idling. But the lights flicker with the misfire (Cluster, Dome, and Headlights).

Last edited by abodah; 01-11-2019 at 05:08 PM.
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Old 01-11-2019, 07:03 PM
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2002 ML 320 & 2006 ML500
When there are bubbles in the coolant it is a strong indication that there is combustion leak, hence cyl. #6 head gasket. This product will let you know.

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