Diesel engine knocking at low revs c250td

P_biggy

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I have a distinct knocking sound coming from a cylinder at idle. The car is a C250TD P Reg. I have just replaced the injectors and glow plugs and the car starts and runs well; the knocking seems to disappear when the revs increase but reappear at idle. The knocking was there before I changed the injectors but not as noticeable as now.

I listened to the noise by putting my ear to a screwdriver on top of the injector and heard a distinct "ting ting ting" from number 2 cyclinder and a faint ting in number 1. All the rest had the usual wooshing sort of noise and seem to function fine.

Is this a timing issue?

Thanks

Phil
 

and11

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Diesel Knock??

Isn't this actually called ' diesel knock ' An adjustment to fuel pump i'm told will cure mine but i found adding rapeseed done the trick. Bearing in mind my old merc is 1989 3 litre straight six non turbo:D I'm sure a clear explanation will be posted very soon.
 

Xtractorfan

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Just to be sure it aint a duff injector try changing it with one of the others and see if the noise moves with it. I'm not a diesel mechanic, but I do know that many modern day injectors have to be coded or set up ; and I have heard some scary noises caused by out of sync injectors...
 

Paid2getdirty

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1983 200D showing 68000 kms
Hi Phil

Been a while since I did any work on one of these but if the timing was out it would affect all the cylinders not individual ones as you suggest. How come you had to change the injectors and glow plugs? was it to try and solve the knocking problem or because of something else? I think these types of injectors are purely mechanical ones. The only electrical aspect to them may be that one of them has a sensor in it to tell an ECU of needle lift postion. I cannot recall if this engine uses an electronically enhanced timing mechanism on the pump. If its not too much aggro as Xtractorfan suggests try swapping them about, its the cost of some washers and the time but it'll tell you if it's the injectors or not.

Gareth
 
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P_biggy

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I changed them all as it hadn't been done for 170k so thought I would give the car a bit of a refresh especially as I had been having some starting (fuel valve solenoid in the end). It certainly runs better although it has accentuated the knocking at idle hence the question.

I did swap out the injector on cyclinder 2 but it made no difference to the knocking at idle speeds. There are no electronics on these injectors purely mechanical; they also don't appear to be coded although there is a purple spot on one side (not sure what this indicates).
 

Xtractorfan

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Right your car has an injection pump so i would get that checked no2 is maybe slightly impotent and lacking.. check the simple options first, noises that go away with revving and faster engine speeds are generally caused by external means like fuel supply etc . more serious matters would get noisier and increase in tone with engine speed ..tho low oil pressure at tickover could be a factor.
 

mister_cee333

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Assuming your particular engine has hydraulic tappets then this could be your fault if they've not been changed in 170k. I once had a similar fault on a petrol 190e.
 

wireman

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nice 201 2.5D 1993 & very nice 129 SL500 1994
Over advanced injection timing has similar effects. This could be as little as 1/2deg and could be wear associated.
 

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