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  #1  
Old 06-14-2003, 01:22 PM
TNM
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300SD shake - idle speed?

Hello All,
I ran two cans of Diesel Purge on Thursday and my car still shakes (which is rather anoying and I can't imagine did form the factory) at idle. I don't like shaking at stop lights. The engine mounts are new as well as shocks. The mechanic told me I probably had an injector not fireing properly at idle and suggested putting diesel purge in the tank. I was convinced that would be a waste of money so I ran it directly through the engine undiluted. Sometimes it seems to shake less but usually it is the same. It runs around 750 RPMs at idle and once the engine is up to 1000 it is totally smooth almost like a gas engine car. Should I just up the idle speed to 1000 RPMs and if I should how do I do it? Or is there some other likely cause of this shake?

Tom - who after unplugging and replugging things in the engine bay has cruise control for the first time since he's owned his SD

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  #2  
Old 06-14-2003, 03:31 PM
sixto's Avatar
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Do a search on 'rack damper' and 'rack damper pin'

Sixto
95 S420
91 300SE
87 300SDL
83 300SD
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  #3  
Old 06-14-2003, 06:45 PM
Holson Adi's Avatar
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Yeah check the rack damper or rack dampener or damper pin. It's basically a bolt with a spring in it that "damps" the pump's vibrations.

Is the idle rough or is it 'smooth' but lopes? As in, is the idle speed consistent or does it go up and down?

Mine used to shake and the idle speed was constant. So, I lowered the idle to a point where the shaking isn't as bad. It still shakes though but... it's part of the diesel thing

good luck,
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  #4  
Old 06-14-2003, 11:44 PM
TNM
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The idle is constant. I know Diesels aren't very refined but, For instance if the car is in neutral it is bearable - I put it into gear and it causes the cabin to shake - I don't believe anyone in 1983 would have paid nearly$40,000 for a car that does that at stop lights. I'm not sure what this rack damper thing is I'ver never heard of it. I'll have to see what it is about.
Thanks,
Tom
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  #5  
Old 06-16-2003, 10:22 AM
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I have an 83 300SD, and this is exactly what mine was doing several months ago. I took it in and had the compression checked. I have two cylinders that are about 100 PSI difference from the other three. Nothing can be done to repair that except to get the top end redone. (This car was severely abused prior to me picking it up. The valves were probably never adjusted.)

I also had the injectors cleaned, which made quite a bit of difference as far as power was concerned, but it still was bad at idle.

If adjusting the rack damper doesn't work, which it didn't for me, the only I could figure out to do was to bump up the idle. I ran mine up to 900 rpm, which is about 50 rpm over top recommended RPM, according to the manual.

It purrs like a kitten now at the stoplights.

I was worried that my tranny might not like it, but I run at freeway speed 99% of the time, so it probably isn't an issue.

83 300SD 174K
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  #6  
Old 06-16-2003, 10:28 AM
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TNM,

This is the classic sign of engine mounts failing. As they age, they become stiff and their natural frequency rises, and in some cases if it rises enough to coincide with forcing frequencies with the engine at idle, you get amplification instead of attenuation of the vibration. When you put the car in gear and the engine idle drops a little and the vibration in the cabin increases, the vibration frequency of the source drops to the point where the problem gets distressing. Take a careful look at your engine mounts and see if they are whole or worn out. Hope this helps. Jim
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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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  #7  
Old 06-16-2003, 10:40 AM
TNM
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as I put in the original post - the engine mounts are new - the mechanic said the shocks were okay - maybe I should replace them - I am having a hard time finding the rack screw everyone mentions ... .
Tom who has noted it is definatly worse when it is warm but, suddenly has been harder to start (since getting the new mounts)
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  #8  
Old 06-16-2003, 10:51 AM
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TNM,

Again, this is EXACTLY what mine was doing. Once warm, it was far worse than cold. It cost me $65 to get a compression check done.

As far as I'm concerned, it was worth it. Once done, I knew what was wrong, and the fact that I couldn't fix it without spending big dollars gave me peace of mind where I intend to go with the car. And that is, "Drive it 'til it dies." Once this gets so bad that I can't take it, I'm going to tear it down and rebuild the whole darn thing.
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  #9  
Old 06-16-2003, 10:59 AM
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The rack damper is behind the injection pump...

the one pointed by the red arrow.

You have to tighten it (clockwise into the pump) to reduce the vibrations.

Don't do it all at once though, do it in small increments otherwise your engine might not be able to idle. i.e, stalls

untighten the lock nut first and then screw in the rack damper bolt slowly.

BTW, there is a new style damper bolt that is supposedly stronger.

I think it's the part called Idler Adjuster Pin under Diesel Injection in fastlane.

also have you checked the engine's compression? what about timing chain stretch?

Good luck,
-Holson-
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300SD shake - idle speed?-pump.jpg  
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  #10  
Old 06-16-2003, 11:27 AM
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I've never seen a primer pump like that.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD
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  #11  
Old 06-16-2003, 01:30 PM
Old Deis
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It should be said again that the rack dampener bolt on the rear of the IP on most of these has been changed to a gold colored bolt by now. There are still some out there that are to old steel color and they should be replaced with the upgraded gold toned.
I have an 81 SD and had a similar shake with the car at one time. There is no magic bullet with most of these to get a smooth idle, but if you are persistant you can sort the problems out and get it to idle smoothly.
First thing is that rack dampener bolt. Pull it out and check the color. If is is plain steel color then order a new one and install it. To adjust the fuel rack dampener you should turn that bolt in incrementally with the engine fully warmed. As it turns in you may see the idle shake reduced. If turned in too far when you rev the engine it will stumble. If after setting it you notice the engine dies when yo bring it to a stop, then turn the bolt out a little. Takes a 14 mm and 12 mm wrench to get the bolt a lock nut tightened.
Next is the valve adjustment and timing chain. There are lots of threads on the best way to do the valves. I found the Haynes Mercedes Diesel manual has an excellent section on the valve settings
Check the timing chain stretch while you are in there. Again there has been some great threads on this. Search for them. I replaced the timing chain earlier this year and was rewarded with a smoother idle on my older 78 300D.
After that if you still have a peristantly rough idle, then it is time to check the start of delivery timing. Not a bad DIY job at all. You will need the drip tube, but it is not that expensive. The Haynes Mercedes manuel has some very good instructions for that also.
Lastly the injectors can need attention. I just took mine into a local diesel injector service and had them rebuilt. Some have had success here dismantling them and cleaning them.
While you are at it run a compression test on the engine. A difference in compression between the cylinders may cause a rough idle.
Good luck, and take your time. This can be a great learning experience.
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  #12  
Old 06-16-2003, 08:29 PM
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Quote:
Originally posted by sixto
I've never seen a primer pump like that.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD
me neither...I thought it was the updated pump but I bought one and it's not as big.

I bought the pump originally to replace mine but now it's a 25kg paperweight...
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  #13  
Old 06-17-2003, 03:16 AM
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at least your papers won't fly away in a hurricane or Tornado.


Plus it's useful to take pictures of to get a point across, always gotta look for the good.

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  #14  
Old 06-17-2003, 11:45 AM
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back to the shaking

Does the running of the air conditioner seem to make the shaking worse? Mine has recently started this...in the morning it's completely fine and drives like new (so I'm told) but after driving a while and then pulling up to a stop light BAM! we begin to vibrate. I'm also getting a clinking noise from the latch of the air filter hitting the valve cover...it annoys me like heck!!
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  #15  
Old 06-19-2003, 01:25 PM
TNM
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Well, I took out the Damper Screw and went to Crown Eurocars the local Benz dealer. generally I have bought parts form them rather cheaply - motor mounts and anything else I wanted. For that screw they wanted $76.14. (oddly they didn't have it in stock either) I told them I'd try to find it cheaper. Performance Products - who sold me my floor mats sells them for $26 plus whatever shipping will be. Is there going to be a diference in quality? I do think there is some noticable difference after replacing the pin (which is silver/old engine colored). But5 adjusting it in and out I really couldn't notice much difference in Idle speed or shake except at extreames of almost out compared to in. Will the one from Performance parts be the same quality as the one from MB? I don't mind paying more sometime even if I"m not really getting more but 3X as much is a bit rediculous.
Tom - who saw a 300SDL in for service there in wonderful shap Blue but with Gray interior instead of that (IMO ugly Blue Mercedes leather).

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