Rack damper bolt adjustment question and cold idle problem... - PeachParts Mercedes-Benz Forum

lietuviai · #1 12-20-2003, 02:45 PM

Rack damper bolt adjustment question...

The following is a thread I origionally posted in the diesel section with one reply and my follow up. I am still looking for more answers in regard to this but it seems that my origional thread has fallen victim to being in the back pages. I'm sorry that there is so much to read but any help from some techs will be really appreciated.
Thanks,
~DJ

I have a slight cold start problem. My 85 300D won't idle on its own when I just start it up in the morning. I have to keep my foot on the pedal until its warmed up a little. Glow plugs are new. I don't want to mess with the idle adjustment as it idles OK when warm. I do get a slight miss at idle before its fully warmed up with a slight variation in idle speed (it goes up and down). It was suggested to me that I adjust my rack damper bolt to fix the problem. I found it turned all the way in and I backed it out a little at a time to the point that it looked like it was almost all the way out but it made no noticable difference. What exactly does this bolt do and is it attached to anything? Do I need to change it and is it difficult to change?
Thanks in advance.
~DJ

psfred
Senior Member

The bolt pushes on a spring on the fuel control rack (the rack rotates the sleeves on the plungers for each cylinder, controls the abmount of fuel delivered per stroke). The pressure is to keep the rack from vibrating back and forth.

If adjusted too far in, you will have trouble starting from insufficient fuel delivery, although you will have nice smooth idle. Speed won't change until you screw it in so far you force the sleeves "closed".

Have you changed your fuel filters and check the tank screen and fuel lines? There are several things that will cause rough idle cold besides bad GP.

Peter

I haven't changed the can type fuel filter since I got the car about 9 mos ago nor have I checked the screen in the tank. The "see through" filter looks clean with no visible debris or discoloring. I'm assuming I have good fuel delivery since I feel a good pulse in the lines. One thing though I have a suspect injector since one of them makes a bit of a noticable tick. I've tried to isolate it by cracking the lines but it seems the tick goes away when I crack any of them but one seems make the tick go away more than the others. If I were to consider replacing it, should I just replace all of them? My thought on the tick is that there is probably a worn spring in one of the injectors. I don't think cleaning them may make any difference since I ran a couple of cans of pure diesel purge through the injectors directly from the cans.
Other than this the car runs great and has plenty of power when at operating temperature.

bjcsc · #2 12-20-2003, 03:21 PM

I am not a tech, but how is your compression? How many miles on your car? That would be the first thing I would check. Everything being OK when warm points to a compression issue IMHO...

lietuviai · #3 12-20-2003, 03:33 PM

Car has just over 220,500 miles on it now. Compression readings were good last time it was checked. Valve clearances are also within spec.

shane83SD · #4 12-20-2003, 03:47 PM

I would start from the least pain (cost) :

1. Adjust the rack damper for smooth "hot" idle. No more, no less.
May not fix it, but make sure it is properly done.

2. Pull the injectors and let shop check for spray pattern and pop pressure. I think there is a high correlation with the slight hunting symtom.

3. You have new glow plugs but would'nt hurt to double check.

Low compression and/or worn IP $$$$.

Good luck.

lietuviai · #5 12-20-2003, 03:54 PM

Quote:

Originally posted by shane83SD
I would start from the least pain (cost) :

1. Adjust the rack damper for smooth "hot" idle. No more, no less.
May not fix it, but make sure it is properly done.

I appreciate all the suggestions. How would you suggest to properly adjust the rack damper?
~DJ

haasman · #6 12-20-2003, 04:54 PM

You might want to also consider running Diesel Purge through the system.

When I owned diesels I did this about once a year and seemed to help with overall running, starting and fuel economy.

How do you find info on this? The SEARCH feature above reveals results such as this: Diesel Purge

Haasman

bjcsc · #7 12-20-2003, 04:55 PM

Hey, take a look at these threads. Maybe they'll help.

Rack Damper Bolt ID (Pic)

Rack Damper Pin Removal/Install

300SD shake - idle speed?

bjcsc · #8 12-20-2003, 04:57 PM

Quote:

Originally posted by lietuviai
I am still looking for more answers in regard to this but it seems that my origional thread has fallen victim to being in the back pages.

Oh yeah, whatever you do, don't post a "Where did my original thread go" in the Open Forum...

lietuviai · #9 12-20-2003, 05:31 PM

Quote:

Originally posted by haasman
You might want to also consider running Diesel Purge through the system.

When I owned diesels I did this about once a year and seemed to help with overall running, starting and fuel economy.

How do you find info on this? The SEARCH feature above reveals results such as this: Diesel Purge

Haasman

I did run a couple of cans of DP the right way and it didn't make any difference.

The exhaust smelled funny while I did it though.

mbshop · #10 12-20-2003, 06:11 PM

i have cured many diesels with cold stalling
problems by just adjusting the warm idle.
i find many cars with low idle.
you must take care of things that have already been
mentioned first though.

george

ILUVMILS · #11 12-20-2003, 06:27 PM

Adjust the valves when the engine is cold. Remove the valve cover and let the car sit overnight. Adjust the valves to the cold spec's. You'd be surprised what a difference this can make.

mbshop · #12 12-20-2003, 07:07 PM

adjusting the valves cold is a new one on me.
where and how did you get this info.?
mercedes likes it adjusted hot. this is where the
engine runs.

george

psfred · #13 12-20-2003, 07:24 PM

It's a lot nicer adjusting the valves cold, especially for us amateurs. Maybe not for a professional. The lash spec on the car plate specifies 20 degrees C as well, room temp.

Specific to the complaint, though -- have you checked the chain for stretch? If the chain is "long", both valve and injection timing will be late, and this will show up as excess smoke, lots of carbon in the engine, rattly injectors, and slow idle. Worth a look at 225,000 miles anyway.

Peter

lietuviai · #14 12-20-2003, 08:35 PM

Peter,

My last adjustment on my valves was on a cold engine a couple of months back. I don't think that they are to blame.
Now on the subject of chain stretch, what is the best way to check for it? I sort of checked it when I adjusted my valves but it was not the way I'm sure you're supposed to do it. As you suggest, it probably needs a look since I do have what seems like a noisy injector and there is some smoke at idle. I'd hate to think about doing a chain replacement when the car seems to run good otherwise. If there is an amount of stretch don't the tensioners take care of that?

~DJ

psfred · #15 12-20-2003, 10:44 PM

Tensioner just keeps the chain tight, it won't do anything else for "stretch" -- really wear on the pins and links on the chain. The length increases, so the cam and injection pump lag further and further behind the crank, reguardless of the tensioner.

Anyway, to check the stretch:

On the front cam tower at about 1:30 or 2:00 position, there is a little nub cast into the tower. The thrust washer behind the cam sprocket is keyed to the cam, and has a notch cut out of it. Line the notch up so that it is centered on the nub and read the crankshaft pulley. Anything less than 4 degrees past top dead center is fine. 4-8 degrees, chain is wearing some, you may want to adjust the injection timing. 8 or more degrees, time for a new chain.

You can get offset Woodruff keys to adjust the cam timing (a new chain usually gets you to about 2 degrees off, no closer), and the IP can be set to the correct time no matter what the chain stretch is.

You may want to try a couple times to make sure you are getting the notch lined up right.

Peter