Engine Knock Woes

Right, where to start. Engine started knocking about 2 months ago. Replaced the fuel filter and all 4 injectors. General service done with all filters and oil change. HP pump replaced.

It is still knocking exactly the same. I really don't know where to look next. It isn't throwing up any fault codes.

Does anyone have any ideas?

Ta,

Gary

Can you describe the knock or better still, record it.

What engine?

freelance said:

What engine?

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BMW M47 engine.

The knock is a real tinny rattle when I accelerate (like a tin can being kicked down the road). Mechanic is 99% certain it a fueling problem.

Try a better fuel, or additive, do you think it could be something loose, baffle in exhaust or turbo wastegate.

Running it on BP Ultimate and had diesel rhino through it many times, no difference.

Look at the crank pulley / damper. Is there shiny metal particles are the area of the pulley? Check the pulley for wobble with the engine running and by hand (engine off). Any looseness of the pulley would point to damper failure. It's reasonably common on the TD4.

nodge68 said:

look at the crank pulley / damper. Is there shiny metal particles are the area of the pulley? Check the pulley for wobble with the engine running and by hand (engine off). Any looseness of the pulley would point to damper failure. It's reasonably common on the td4.

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+1

Nodge68 said:

Look at the crank pulley / damper. Is there shiny metal particles are the area of the pulley? Check the pulley for wobble with the engine running and by hand (engine off). Any looseness of the pulley would point to damper failure. It's reasonably common on the TD4.

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Would this cause a puff of black smoke at the exact same time as the knock?

Nodge68 said:

Look at the crank pulley / damper. Is there shiny metal particles are the area of the pulley? Check the pulley for wobble with the engine running and by hand (engine off). Any looseness of the pulley would point to damper failure. It's reasonably common on the TD4.

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GMC85 said:

Would this cause a puff of black smoke at the exact same time as the knock?

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No it wouldn't, sounds to me like you have an over fueling problem, a decent scan should highlight the fault.

Engine started knocking about 2 months ago. Replaced the fuel filter and all 4 injectors. General service done with all filters and oil change. HP pump replaced.

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so low pressure pump is ok ?

sounds to me like you have an over fueling problem

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if it's over fuelling maybe check the maf sensor ..
and air-intake-temp. sensor .. if a separate one is fitted ..

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IF it's def. diesel knock ( and not something like loose exhaust baffles )
maybe check:
the fuel-rail-sensor plug and socket for corrosion on the pins / dirt / grime on same
or if the plug-socket are tight fitting ..
the maf sensor ..
the turbo map sensor ..
that the injector wiring plugs are all clean and free of corrosion ..

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common-rail design got rid most of the old diesel type knock ..
by .. amongst other things .. having multiple fuel injections per piston power stroke
( unlike the single injection on older designs )
the "knock" being a shockwave from the combustion process

i'd be inclined to check the fuel rail pressure sensor wiring connection first ..
cause it can evidently cause all sorts of weird symptoms ..
and it's a main factor in controling the fueling

then i'd check the maf sensor ..
and the air-intake temp sensor if it's got a separate one
( earlier models use the maf sensor for that )
then the turbo map sensor

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i used to have a bit of diesel knock when using regular shell diesel ..
the slight tinkly knock was on partial go-pedal .. lower rpm
( i tried their premium stuff but got worse mpg
( and felt like i'd lost some torque as well ..
so i stopped using shell products ..
( could have been just from the one station i used to fill up at )

after that .. ( and with continuos use of diesel rhino 'n a splash of 2stroke oil )
the knocking slowly vanished ..
would only happen in hot weather .. and didn't notice any smoke ..

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hope the service includes draining the sedimenter ..
( easy to do if the service staff forgot )
usually done once a year .. best just before winter ..
( to make sure there's no water getting into the fuel )