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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

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  • 1
    try watching voltage at the pump when this happens.
    – Ben
    Aug 5, 2016 at 19:27
  • when this happens ECU also send constantly signal to open/close fuel pressure and volume regulator on the pump.
    – ArnyPP
    Aug 5, 2016 at 21:38

2 Answers 2

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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.

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  • Once again thanks all for help. Idle seems to be ok, single small shakes approximately in every 4-5 seconds , but when I hold 1100-1200 rpm car have much more shakes/vibrations. There are some air bubbles in the fuel line from time to time. It happens also when I go to small downhill from steady ride and car needs to drop speed, feels like fuel pump drops pressure stepwise with jerks.
    – ArnyPP
    Aug 6, 2016 at 9:34
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    It is not normal to have air in the fuel line. How did you found out about the air? A classical candidate for the air would be a leaking seal at the fuel filter (assuming a self priming high pressure pump)
    – Martin
    Aug 6, 2016 at 12:14
  • there is a clear pvc pipe between high pressure pump and filter housing. no leaks at all. filter housing has new sealing ring. if there was some crack, fuel should flow back to tank then engine stops?
    – ArnyPP
    Aug 6, 2016 at 14:29
  • Do you mean the (if present ) feed-back line? In what direction do the bubbles go? Please post the exact model of the car
    – Martin
    Aug 6, 2016 at 19:52
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    Does this happened after a recent fuel-filter change? If yes: Bleed the system by disconnecting the green connector (this is the return line, near the fuel filter) and use a vacuum pump to pump out diesel until the diesel has no more air bubbles. The next time use the plugs from the fuel filter kit to close the fuel lines while changing the filter. Also fill the filter housing to the top with fresh diesel. If no: There must be a leak/crack in the hose/filter housing or the filter housing is not perfectly closed
    – Martin
    Aug 7, 2016 at 21:32
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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.

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  • already new filter. hmm maybe I should try to clean the fuel tube (between the tank and pump) by air pressure one more time...
    – ArnyPP
    Aug 5, 2016 at 21:40

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