I know next to nothing about diesels so bare with me please. The engine has a rather loud knock at startup -- on a gas engine this would be a real warning sign to me. After the engine is warm it sounds like a bus (normal diesel to me) and seems to run fine. There seems to be very slow acceleration on take off until the turbo kicks in and then its plenty strong -- I have not driven these before but seems about right for what i'd expect from a diesel. Very little outgas when driving and once hot hardly any gas from exhaust. Under the hood the rear most injector was wet on the outside. I am guessing it is leaking and may be stuck/sticky and that cylinder doesn't fire initially until the engine is hot. Would I be about right on my guesstimate? Is it bad to have one cylinder slapping about like that w/o firing? Could I be wrong and it be something else. The car is for sale , has about 170,000 miles and rebuilt or junkyard transmission (not sure which but trans was replaced recently) AC operable asking price is 2k USD what do you guys think? seems to run fine after being hot but when cold the knock is quite noticeable

ps: the odometer seems to be working but the car was owned by a mechanic before the present owner bought it 4 years ago so I am unsure if this is actual 170,000 miles on the engine but the present owner says it is correct

1983 300SD not 1985, was given bad info.sorry

People may have been reluctant to post as it could be a rod bearing. Loosen one injector line at a time till the knock stops. Switch injectors with one close by. Do the line test again on those two cylinders. If the knock does not trasnsfer to the new cylinder proving an injector problem it might be a rod bearing. Not an unknown defect with these engines. A remote chance exists of an injection pump deficiency as well. Just not a strong possibility.

Check things like the vacuum pump with a hose to your ear as well. Might localise the sound.

Could be something else but what? Maybe this post will get your thread going.

I have used a metal rod that I place on different parts of the engine, place it to my ear. works like a stehascope sort of.

maybe you can localize the point of the knock.

the last injector leak could be the return line or the side close to the firewall has a plug in a short piece of return line.
the plug can be reused, pull it off and slice the side of the hose. push it into a new piece of hose. be careful of the 2 nipples of either side of the injector the hose fits on. don`t want to ding them.

charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

thanks barry and chuck...


i will see if the owner will let me get to the car to try the switch on fuel lines

question : if the knock disappears when its hot would that help to rule out a rod bearing? engine is the normal tiny sounding diesel sound after its fully warmed up

i asked the owner (speaks spanish so translated) and he said that one of the injectors is dirty but they don't cost much to buy

am i correct that if the sound goes away when fully hot that its unlikely a rod bearing?

please forgive my ignorance ---- i know much on gas engines but a total newbie on diesel

i really appreciate your help!!!!!

if worse case and the engine needed an overhaul...any idea what that runs on average for these?

Simply put if there is money involved here eliminate or prove the faulty injector problem. Could be the difficulty. Rebuilding one of these engines is really expensive. A good used engine is usually the route taken instead when it is required.
You would think that as the oil thins as engine warms up. Rod bearing would get noisier. That is not an absolute certainty on these engines perhaps. Do some tests with the injectors. Or pull them and have them checked out.

If it is not a real rhythmic sound it is likely injector nailing. My 240D is starting to do this now, I need to rebuild the injectors. You may have luck running a "diesel purge" through it. Use this as a bargaining chip to lower the price, but it is probably not a big issue. Plan on $500 to have the injectors rebuilt.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

i found injectors http://www.*********.com/catalog/1983/mercedes/300sd/diesel_injection/diesel_injector.html 42$ i am surprised a rebuild of them is 500$! wouldn't it be more prudent to replace them? i may be wrong so just let me know

My local shop quoted me $60 for a nozzle plus $25/injector to rebuild = $425 for a set of 5. Not quite $500 I guess.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Since you're a newbie to diesels, you may be just experiencing normal diesel clatter. Post an audio recording to see if we can hear anything out of the ordinary. Without verification, for all we know, you may have no prob at all.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

If it is NOT one of the above problems then drop the lower pan and see if the oil pump relief valve is still screwed into the back where it should be... consider replacing it if still in place with the " C " variety as listed in the FSM. It has a different relief pressure and different shape vents. Long shot but is listed as possibility in the FSM for what you may be hearing... check the other stuff first though... since we are only going on your description of the noise. If it just fell out you can use sealant to keep it in place.. like red locktite.

yes I'm a total newbie on diesels

is it possible they just knock at startup and then sounds more even/normal after up to operating temperature?
i have had others tell me they ALL knock at startup
does this sound right?

i am going to try to see the car again soon and i'll take a recording

thanks again

If it is not the injector, it could be a piston slap, in which case, when the engine is cold, the "slap" mimics a bearing knock, and would be the loudest . As the engine warms up, it will slowly go away. A piston slap can be described as a piston rocking back and forth in the cylinder walls due to excessive wear and too much clearance. The other thing you might want to check out would be the glow plugs. If one or two are not working, the engine will sound like crap until is warms up....good luck..

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96 E300d