4

Now its my turn..

Volvo 2.0 diesel Siemens VDO

When car gets warm, in 4th - 6th gear, the car starts shaking between 1800 - 2200 rpm, no warning lights. Diagnostics show that the fuel pressure drops and goes up again all time. It happens only at stable ride, when you accelerate harder or release the gas pedal, the condition disappears.

I checked the;

  • injectors, works good
  • replaced fuel pressure regulator, still nothing.

From 1st to 3rd gear, no shakes.

Should I replace the fuel volume regulator or even the fuel pump?

Could it be air in the fuel line?

Could it be a DPF filter regeneration bug?

I have no idea....thanks in advance

DucatiKiller
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ArnyPP
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2 Answers2

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The volume regulator at the high pressure pump would surely be a good candidate for the mentioned symptoms. Normally the volume regulator seems normal when accelerating (because he is mostly open, so there is a buffer on pressure incase of a sudden load increase), when releasing the gas pedal you also wont feel it since the thrust of the car keep the engine in motion. Mostly on stable riding any eventually problems regarding the regulation speed will arise.

How does the car behave while idling?

The background on the volume regulator : A high pressure pump must provide enough throughput with matching pressure while the engine is under 100% load. That demands a high amount of energy. When the engine is not under full load most of the pressurised fuel will get feed back to the low pressure part through the pressure regulator. However this is a waste of energy so it is a good idea to regulate the throughput of the pump while the engine is at lower load. That happens with the volume regulator that cuts back the amount of fuel getting in the high pressure part of the pump.

This is my replaced volume regulator, please note the slight fretting marks on the part in the center.enter image description here Those marks where enough to cause a disturbed idling and engine stopping when accelerating after longer descents.

Martin
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maybe there is some gunk in one of the diesel strainers/filters between the tank and the injection pump. (on my car, there are three such devices.) One of them being obstructed, even if intermittently, could negatively affect fuel pressure.

Aaron Brick
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