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Old 12-13-2013, 12:24 PM
psaboic's Avatar
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Join Date: Jun 2004
Posts: 1,250
Knocking sound

Hi all,

Just noticed an issue starting on my 83 300D, and I would like some advice. I have noticed a knocking/moderate hammering sound when the car is started and the motor is cold. It does not knock at idle, but only if you lightly rev it a bit or put it under load when it is cold. Also, it does not knock if you rev it more aggressively. When driving if you put it under moderate load from about 1200-1500 RPM, you can hear it knocking a bit unless you either back off on the accelerator or accelerate more aggressively. Above 1500 RPM it seems to go away.
Once the car warms up the sound pretty much goes away. On occasion you can make it knock a bit if you rev it moderately off idle, but the sound is much softer when the engine is warm. On the highway it runs fine, with no knocking, but I have noticed a tad rougher idle if you are sitting at a red light.
Oil pressure is fine at both idle and on the road, oil level is fine, and it runs and drives normally. I have noticed that the exhaust has more black smoke than it used to, especially in the cold weather. The injectors as far as I know are original and have about 270K on them. I plan to have them done in the near future. It is also due for a valve adjustment and oil change in about 1500 miles.
So…What do you think, injector knock due to worn injectors, or something more sinister.
I have described it as best as I can, and I am not able to post a sound clip or video right now as I am on the road for work for the next couple days.
Thanks in advance for any advice/help

Glenn
__________________
2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)
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