I just aquired a 1983 240D with 189,xxx miles. It has no power and what I would call a signifigant engine knock. Max speed I can get it up to is 35 on level ground. It is my goal to get this car back to good shape. I would like this to be my daily driver. When I bought it I knew it would be a project and I am willing to put the time and money into it. A group of my friends and I are looking forward to working on it. We all have some mechanical experience but this is our first diesel project!

This is what we have done so far (I know its kinda lame but we had to start somewhere) Changed oil, oil filter, air filter, spin-on fuel filter, and in-line fuel filter.

We are planning to do valve adjustment and diesel purge Saturday.

I need to know what I need to look for and what to inspect to diagnose the engine knock. Is there anything I can do while I have the valve cover off.

I plan on replacing the timing chain, transmission filter and fluid, power steering filter and fluid, and replacing the injector nozzles with bosio nozzles. I want to do all this but I want to get the engine knock fixed before all of this. If I have to do a total overhaul I am looking at some serious time and money so these will have to be later. I would also like to do the work myself if at all possible. I can also take any pictures that you would like me to throughout the entire process. Thanks!

what about the in tank screen. that could be pretty clogged.

I plan on changing the fuel tank screen when I replace all of the fuel lines. This is on my to-do list but I am afraid that all of the maintence repairs are back burner issues until I can get the major engine issue solved. I think I will be able to rule out the tank screen as the major power issue when I run the purge. I can run diesel through the "mini tank" and see if the power increases.

The first thing I would do in your situation is clean the tank screen and blow out your fuel lines.

Tank Screen Removal - Pictorial

Blockage in your fuel delivery is probably why the car is going so slow.

Good luck.

Scott

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Scott
1982 Mercedes 240D, 4 speed, 275,000
1988 Porsche 944 Turbo S (70,000)
1987 Porsche 911 Coupe 109,000 (sold)
1998 Mercedes E300 TurboDiesel 147,000 (sold)
1985 Mercedes 300D 227,000 (totaled by inattentive driver with no insurance!)
1997 Mercedes E300 Diesel 236,000 (sold)
1995 Ducati 900SS (sold)
1987 VW Jetta GLI 157,000 (sold)
1986 Camaro 125,000 (sold - P.O.S.)
1977 Corvette L82 125,000 (sold)
1965 Pontiac GTO 15,000 restored (sold)

Knocking or nailing?? Stethoscope works well for isolating either to one or more cylinders, precomb chambers (nailing)..... wristpins or conrods at lower end (knocking). The only reason the crank conrod bearings or wristpins should fail is if the engine was run out of oil.

And since this is your first diesel project then resist the temptation of diagnosing a dead/dying engine too soon...... 189k miles is nothing for the 240D.

These cars experience problems with the pump linkage quite often. Have someone push the pedal to the metal and see if the pump arm is fully advanced. If not examine the linkage for the fault. Sometimes the rubbers are missing from the linkage as well. I suppose they rot and fall off with time. As for the knock. Loosen the injector lines at the injectors one at a time. Once you have found the cylinder that is knocking swap injectors to see if it goes away. I would tend to concentrate on the knock as well.

Barry, thats precombustion chamber nailing you're talkin about that follows suspect injector from one cyl to another. Gotta keep our terminology straight.

Diesel dog, you are probably right. What I was thinking was it might be a defective injector starting to unload fuel earlier than it should because of a weak internal spring causing a combustion knock. Or an injector just leaking fuel. Fuel is introduced earlier than it should be either way. Allow that I am tired this evening. Another thought was for some strange reason the 240d loves to develop a #1 bad rod bearing in far too high a percentage of cases to be random. If his knock goes away with the number one injector line loose this is probably not going to turn out very well. .

I am pretty sure (99.9%) the knocking I am describing is not precombustion nailing. If it is nailing it should decrease with a valve adjustment or injector nozzle replacement. As for the wristpins or conrods I am not sure about that. Without using a stethoscope, just my ear it sounds like it is only one cylinder that is knocking. I can not guarantee that this was not run on low oil at some point in time. Ouch!! I know! The oil cap has a small slow leak and I have new metal one on order. There was a fair amount of oil on the valve cover but that could all be from the cap. When I changed the oil after I bought it the oil level was fine on the dipstick and I drained what I would estimate as 6.5 quarts so the oil level was fine when I bought it. One of my buddies said it sounded like a bearing to him but since this is our first diesel we didn't know what bearings to look at. Also from the sound it seems to be on the top (closer to the valve cover) than below, but that is just guessing once again. I want to learn as much as I can and become comfortable with working on this engine but I think this whole diesel engine thing will take us a bit to get used to.

Ok I am now crossing my fingers for nailing. I guess maybe I have never heard bad nailing so I am hoping that is all it is. Ok worst case scenario if it is a bad rod bearing what am I dealing with here. Is it something I can fix or would that fall into the major overhaul category?

Actually we rarely overhaul these engines, we just find another and swap it in. Rebuilding these engines is rather costly compared to the value of the car. We can usually find a wrecked one, one that rusted out, bad tranny, etc.....
Good luck with your diagnosis. You have received good advice above.

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

It is probably not a bad rod bearing. It just could be. Rather than being concerned right now about possibilities just try to localise what it may be. Start first by loosening those injector lines off one at a time and listening for a knock reduction. If and when you get any indication of a reduction do the next logical step. There are lots of good refferences to knocking in the archives to look at as well.

You should definitely do what Barry suggested in cracking open
each lnjector line while the engine is running. Once
you cracked the injector, it will not have enough
pressure to open and spray. This will create a dead
cylinder and no combustion pressure in that cylinder.
You can tell if you have a bad wrist pin or bearing on that cylinder because the sound will go away when there is no combustion pressure. Or to find out if it is a bad injector, replace it with one from another cylinder… you may have to repeat it again with another injector to be sure.

As far as replacing that particular bad
rod/bearing/pin, your going to have to take motor out and head off. You can get away with replacing only one piston if that cylinder wall specs out to its service limits and the crank journals are good condition.

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1983 123.133 California
- GreaseCar Veg System

As occasionally happens a later thought or two comes to mind. Since I am not present and all knocks do not sound the same it is a bit of a crapshoot to suggest things. Another thing that came to mind though was a loose damper pulley on the crank. I have not had one on these 123 diesels but quite a few have. If I recall correctly a few of those people described it as a knock. Again this is something it probably is not but so easy to eliminate in a minute or two as a source. Another source could be the vaccum pump again a little obscure but still a remote possibility. Listening on a screwdriver handle as a stethscope would isolate it fast. Again the two items mentioned are long shots but possible.
Right now you are learning a lot about diesel charactaristics first hand. That is a good thing. They do get easier with time. I hope you continue to post as you go along with this car. It not only helps others but allows further helpful comments to be made by many site participants much smarter and with greater abilities than myself. I have never found any evidence of members not trying to help out to the full extent of their individual ability and experience. We if fact learn from each other in a continious fashion from our ongoing experiences. I estimate that over 98 percent get enough guidance to either localise or repair the problems posted. Did you have a quick look or examine if the pump linkage was the fault causing the low speed yet?

Ok we worked on the 240D this morning. Not a lot of progress but checking things off and eliminating things as we go. Here is what we did this morning:

We examined the pump linkage. Seems to be it great working shape. The pump is wide open when the accelerator is at the floor. We cleaned and regreased all the ball and socket joints since we were looking closer there. They all had plenty of grease and all popped out very smoothly and went back in just as smooth.

We adjusted the valves and replace the valve cover gasket. They valve weren't as far off as I had expected. It seemed that all of the intake valves were pretty close. 2 or three of the exhaust valves were tight though.

Elminated the fuel tank screen. We made a mini tank (like used in the diesel purge) filled it with fresh fuel from a good source and took it for a spin. Still now power.

Disconectted each injector line while running. The knock never decreased, eliminated, or changed.

Ok so after all of that work this morning we still have no power what so ever. It shifts through the gears fine while driving at what sounds like the proper RPM. The engine knock is still very present. My diesel purge did not arrive today so I was unable to perform that today, however I am not sure how much that is going to help any of my problems. I will check the vacuum pump and all pulleys. Just a little more on the knock. It is very rythmic, and it increases in speed and volume as the engine increases RPMS.

Ok next steps, anymore suggestions?