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  #1  
Old 10-18-2005, 06:10 PM
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glow plugs = knocking??????

I have a 300sd (83) and trying to combat a knocking issue. I have read on here to check your glow plugs. Could someone explain what that has to do with it. I thought the glow plugs "heated up" for ignition? Then turn off after the engine has started. If one plug was bad would it cause that cyclinder to never ignite (that may be a stupid question)?

I pulled the plug out of the cyclinder that seems to be doing the knocking (opened the fuel line and it stopped), which switching the injector didn't seem to fix and after I replaced the glow plug the knocking stopped.....for a little while. The plug was pretty hard to get out....there was a ton of black gunk around it. I later read that there is a "reamer" tool used to clean the opening. If the opening is all gunked up....does it cause that plug to faulter?......And, then again it leads me back to my original question....even if that plug is bad....if the engine started....wouldn't that cylinder still fire up? Why does that have anything to do with knocking?

rshafferdc

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  #2  
Old 10-18-2005, 08:28 PM
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Quote:
Originally Posted by rshafferdc
I have a 300sd (83) and trying to combat a knocking issue. I have read on here to check your glow plugs. Could someone explain what that has to do with it. I thought the glow plugs "heated up" for ignition? Then turn off after the engine has started. If one plug was bad would it cause that cyclinder to never ignite (that may be a stupid question)?

I pulled the plug out of the cyclinder that seems to be doing the knocking (opened the fuel line and it stopped), which switching the injector didn't seem to fix and after I replaced the glow plug the knocking stopped.....for a little while. The plug was pretty hard to get out....there was a ton of black gunk around it. I later read that there is a "reamer" tool used to clean the opening. If the opening is all gunked up....does it cause that plug to faulter?......And, then again it leads me back to my original question....even if that plug is bad....if the engine started....wouldn't that cylinder still fire up? Why does that have anything to do with knocking?

rshafferdc

Yes if the engine started then the cyl will fire reguardless of GP working. The knocking could be the result of this black gunk. Do you have any smoke?
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  #3  
Old 10-18-2005, 08:45 PM
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Yes

Yeah, I have smoke on start up....light in color, but after the car warms up the smoke is gone. Actaully when the car gets heated up the knocking worsens and the smoke disappears. On start up the knock is pretty small.

I have a history on the car.

Bought it for $200 a month ago from a young couple who NEVER did a single thing for the car. All the fuel lines were cracked and leaking...filters years old. Car started, but shook badly on idle...went 10mph max blew TONs of white smoke, engine strained horribly.

I pulled the turbo to make sure it wasn't seized...it was good.

Read a bunch of stuff on here to help....changed all the fuel lines and filters. NO CHANGE. Thought...stupid bad previous owners....diesel.....GAS!!!!!! yeah the fuel was the issue. Ran "new" diesel through like diesel purge and it came back to life.

Ended up having just a little fuel left so I filled it up and put a bunch of diesel fuel treatment in (two tanks since then)....Right after I regained the power from the new fuel I took it driving on the highway to clear out things. Only about an hour drive and by the time I returned to city driving the knock was present. Since then I have diesel purged, injector swapped, valve adjustment (twice to make sure), cleared out all the goop in the alda banjo bolt (a lot like what was in the glow plug hole), checked the other banjo bolts with the fuel lines (that I could find).

I found another posting that sounded a lot like mine but the "reference posts" suggested are gone. The metalic sounding knock appears top front...worse after warmed up...increases rate with increased rpms. Loudest on take off from a start....masked/gone on the highway. Power feels fine, acceleration feels good.

Would any more info be helpful?
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  #4  
Old 10-18-2005, 08:52 PM
BusyBenz
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Glow plugs do not have anything to do with knocks, or nailing, after a diesel is started up and running many minutes, or up to temperature.

If your diesel engine is knocking, and or what we call "nailing" if this is all in the same, less "rod knock", which I would very highly doubt in any Benz, it is (injectors nailing) In this case, you may have worn injector nozzles, or out of balance injectors, to begin! Lets not get too deep, and assume the easiest befor.....

#1. Install new fuel filter.....#2. Run direct (by-pass tank) Red-Line, LubriMoly, or Power Services, diesel fuel additive.....it'll run solely on this stuff, trust me, and it will clean your fuel delivery all the way to the combustion chamber and is safe......

Try this and then report back.......BB
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  #5  
Old 10-18-2005, 09:06 PM
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more info

I have run 2 cans of lubro Ml. diesel purge..which quieted it down some. Ran red line diesel additive with just a little bit of "new" diesel in a pitcher (like diesel purge) through the system which did nothing. I have changed the fuel filters under the hood twice now.

Today I put a set of injectors in the car which I pulled from a "junked" car with approx 250k on it (just like mine). These injectors didn't look as clean as the ones I had in the car, but I wanted to see what it would do and I found a place in Austin which will check the injectors free and rebuild for $20/each (so I can take the original injectors to them).

Surprisingly, the different injectors didn't appear to change the knock in any way except it sounds louder now on idle and quieter on take off.
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  #6  
Old 10-18-2005, 09:22 PM
t walgamuth's Avatar
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this sounds

a lot like the problem larry bible had on his. i think it was larry. the timing on one cylinder was off at the pump. the place the metal fuel lines screw on the injection pump is a threaded fitting. minute adjustments on this will affect the timing on each cylinder. you need to mark your starting place carefully and then change the postition of it very minutely one direction, then lock it down and start the car and see if it is better or worse. if better turn the same direction til it gets worse then back it off to the sweet spot. if you initial turn makes it worse stop and go the other direction.

but before doing anything i would check with larry and see if he agrees that this fits your description.

tom w
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #7  
Old 10-18-2005, 09:28 PM
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was looking at that

I did read a little bit on this from the hanyes repair manual over the weekend....I will be REALLY honest about it though.....the manual really sucked on explaining this.

I think the problem is people like me don't always understand some of the terms used or "names" of some of the stuff (I don't mean things like fuel pump, but parts on the fuel pump for example). I understood about taking the lines off the pump and all, but NO clue on what do adjust on the pump and the manual talked about "tilting" the pump back or forth...I was REALLY lost at that point.

Should I PM Larry or what is the most polite way to ask someone like him on this site....I don't want to irritate him by any means.

Rick
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  #8  
Old 10-18-2005, 09:50 PM
t walgamuth's Avatar
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sure pm him

i doubt he will not like it. if he is busy he just wont answer right away.

tom w
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #9  
Old 10-19-2005, 10:09 AM
LarryBible
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Rick,

I doubt that the glow plugs have anything to do with the knock.

By swapping injectors you have eliminated what I would have expected to be the most likely cause OTHER than timing. Next time, though, don't replace the whole set. Simply swap the injector from the knocking cylinder with the injector from a different cylinder and see if the knock follows the injector or stays with the original hole.

You MUST set the start of delivery. I'm not sure why the Haynes procedure is not working for you. I learned how to do it from a Haynes manual about 15 years ago. If setting the start of delivery doesn't cure it, then it is either mechanical (inside the engine) or the IP.

Best of luck,
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  #10  
Old 10-19-2005, 01:32 PM
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Where to get the tool

Anyone in Austin have the "tool" used to set the drip timing? Anyone know a good place to get it?
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  #11  
Old 10-19-2005, 03:30 PM
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Samstag Sales, Performance Products

Mercedes dealer? Even Fastlane can get it with the part #.

Part# 636 589 02 23 00
$23@ Samstag
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  #12  
Old 10-19-2005, 07:39 PM
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I'm going to pipe up here and share an experience I recently had with one that was knocking ('83 300SD). First I have a question though. Do you hear the knock while starting the car prior to the engine "catching" and running on it's own?

The reason I ask is because I just recently had one over at the house that was knocking. I could loosen up the #1 injector and the knock would pretty much go away. My first thought was that the car needed a valve adjustment. Adjusted the valves and the car continued to knock. The car started very easy cold or hot and ran out real well with no excessive smoking or shaking. Anyway, while I was nosing around under the car (it was on the lift) I noticed that the oil pan had been somewhat smashed. In talking with the owner he said that he had records from the previous owner where they took the car in to an independent and they were unable to ascertain why the car was knocking. Anyway, I pulled the lower oil pan and there were some pretty good sized chunks of aluminum laying in it. Took a flashlight and looked up into the #1 cylinder and I could see where most of the piston skirt was gone. I can only surmise that when I loosened up the #1 injector then this "unloaded" the cylinder and made the knock go away. This type of knock is called piston slap. If yours does not knock while cranking with the starter prior to running then this is probably not the same issue.
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  #13  
Old 10-19-2005, 09:07 PM
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more info

The car smokes on start up (with little knocking) and stops when warmed up, thats when the knocking actaully become noticable. The idle does shake a little here and there, but much better since the "bad fuel" is gone.

I can not hear any knocking on start up. As I wrote before...the knocking only started after I took a long drive to "clean out" the rest of the bad fuel.

When I "crack" the metal valve lines to release their pressure....all the injector lines except number two actaully cause the idle to stagger.....when I open line 2 the knocking stops.

The car never lost oil or its pressure....who knows how long it had been since it had been changed though. There does appear to be a lot of "old" gummed up oil in lots of places though (glow plug holes...alda line) and I think I mentioned before the car sat for quite a while before I got it.
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  #14  
Old 10-19-2005, 09:44 PM
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Quote:
all the injector lines except number two actaully cause the idle to stagger.....when I open line 2 the knocking stops.
I don't think that is a good sign.
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  #15  
Old 10-20-2005, 12:54 AM
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why?

Jim:

You definately know that I appreciate all your help and advise, but why would you write, "I don't think that is a good sigh"?

Without your reasoning of why you feel this way, how am I suppose to understand or learn anything about my problem?

I don't think I have read anything on here that says anything other than opening up the lines will either cause the knock to go away or not. And, why does it not make sense that if you open up a "good" line it would cause pressure to drop on all the lines? Especially if it were for just a brief second, then it stabalize. Are each of the lines coming off the injector pump all part of the same presurization system or do each of the lines act completely independantly of each other?

Are you thinking the IP is going bad???? Do you still think a rod is bad?

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