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I recently had the timing belt and water pump changed on my Volvo s40 (2006 2.0D diesel). The mechanic also cleaned and adjusted the injectors. After the service I noticed that att some rpms the engine started to "self-oscillate" at a low frequency, maybe 2-3 Hz, enough to get the whole car shaking. It appeared mainly in gears 3 - 5 and between 1800 - 2200 rpms. I have tried to pinpoint the rpms where this occurs while running in neutral, but it seems to mostly appear when the engine is under load.

The second effect was that the fuel consumption started increasing. For years it has been around 7.4 liters per 100 km, and now it is at 9.3, so a 25% increase.

I went back to the mechanic and he looked through the timing belt and water pump change, but could not find anything wrong. After some more investigation he found that one of the glow plugs needed changing, so he did that. This had no effect on the main problem of the "self-oscillating" phenomenon and the increased fuel consumption.

I am no mechanic (obviously), and I am wondering what could be the cause of this problem. It is sort of subtle since the car has to be driven for it to appear, which makes it harder to explain to the mechanic without sounding like I am imagining things. Could it be an error in the injector adjustment? When the engine is under load I guess more fuel is needed for a certain rpm so maybe that could explain why it is hard to reproduce in neutral?

I am not sure what to say to the mechanic to get this problem fixed. Any insight would be very helpful.

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  • It sounds to me like the timing is off but I could be very wrong. Does it only do it in gear?
    – method
    Mar 9, 2017 at 7:00
  • I'm not sure. It is at least harder to reproduce when not in gear.
    – FeatureCreep
    Mar 10, 2017 at 5:06
  • I got same problem with my 2010 C30 2.0d. Have you solved the problem and if yes can you explain how? Regards
    – Fabrizio
    Mar 18, 2019 at 18:15

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Please state the exact engine code, it would be also nice to know the exact work that he did there.

Just some informations on injector maintenance:

Injector maintenance is a very complicated thing, also adjustment on common rail injectors (I suppose that's the case with your engine) IMHO is extremely complicated perhaps even not possible for certain types. Normally the injectors get measured in the factory and receive a special code designating their flow characteristics, the code then get programmed in the ECU. Should the injector flow characteristics deviate from the specific values an overhaul/replacement is needed. Injector overhaul is a work for real specialists, requiring special training and expensive equipment.

I think that it is quite important to solve this issue ASAP: A defect injector could either:

  • produce a constantly burning flame, damaging the piston/cylinder wall
  • run too lean, thereby overheating the combustion chamber
  • produce an asymmetric jet, thereby concentrating the heat on regions that are not designed for it

My personal strategy on this problem

I would ask the mechanic for a flow measurement, albeit he should have offered that to you after you mentioned the problems. If you would have a bad gut feeling I would search sadly another mechanic.

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  • Translated from swedish, so let me know if something looks odd. The work spec says that they changed four injector gaskets, so that would be related to that adjustment. Other things: water pump, coolant, fuel filter, brake fluid, washer fluid, oil filter, motor oil, air filter, varying parts related to the timing belt change (don't know the exact translation). Not sure about the engine number, but it is a 2006 volvo S40 2nd gen with a 2.0 D diesel engine (Peugeot I think).
    – FeatureCreep
    Mar 19, 2017 at 8:19
  • The injector gaskets indicate that the injectors where removed. It seems that the mechanic either suspected the injector gaskets to be defect or he wanted to clean the injectors. You could take a look if there is fuel leaking out from between the injectors and the engine. Then I would talk to the mechanic and tell him of a vibration/strange sound of the engine under high load. My theory: Either the gasket seat is dirty / was not re-milled or something went wrong when cleaning/removing the injectors
    – Martin
    Mar 19, 2017 at 10:40

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