I have a '79 300 S.D with 230,000 miles that I have had for a few months. When I start the car it runs very smoothly. After I run it for about 3 miles or so, or when I let it idle, it idles rough, but only after it is warmed up. No drive ablity problems. I put in rebulit Bosch injectors. The next thing I plan to do is to check the valves and check the timing chain. Any other ideas would be greatly appericated. Thank you!



Candy Verbeck

Greetings Candy,

You say it idles rough after the engine has warmed up? What is the RPM setting at while idling? Could be to low, tach should indicate around 750 to 850rpm. There could also be a problem with injection timing. Does is seem to blow black smoke while it sits there idling? You may have to put your hand at an angle to the tailpipe to realize it's doing this, not always visable just by looking at the exhausting gases puffing out the pipe. The next thing to check is engine temp while the car is at idle. Is it at 80 degrees C or close to it, or well below or above this temp? I've noticed that the engine on older 300 series diesels run better after warmed up because the thermostat has opened up and coolant pressure is no longer an issue in a somewhat back pressure coolant system. Post your observations and I'm sure we'll all try to get this figured out for you.

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

When you say rough what do you mean. Is it missing or does the engine shake? You may need to change therack dampener on the IP. Mine idled rough at first after is warmed up. After I changed the dampener it smoothed right out.

__________________
Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel

Thank you for the help.In the process of adjusting the valves, so far some of them seem tight.

For the rpm is around 800 rpm. The idling is not missing, I get 28 miles per gallon. Does the rack dampener control the rpm on the ip? If so, I played with the rpm and still the idling is a little rough. I have check the motor mounts, and I will let you know after I have got the valves ajusted what happnes. Thanks again, much appericated.

The rack dampener has nothing to do with the idle speed. It keeps the fuel rack from 'hunting' for the correct position. Try moving the stop lever right on the IP slowly to the stop position.Do not stop the engine just slow it down.Does the shacking stop?. If it does it is the rack dampener. You can try adjusting it but you will likely need a new one. Cheap and easy to replace.

__________________
Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel

Thank you very much for your help! Merry Christmas to all!

Mark,

I tried what you suggested about the rack dampner,and I even removed the spring loaded bolt, checked it for tension and the it is very stiff. Then I tried adjusting the rack dampner out, but the only way I could get the car to idle smoothly was around 1000 rpm. I also adjusted the valves and some of them were out about 5 to 6 thousandths on the tight side. Anything you suggest? Thank you and Merry Christmas!

Candy Verbeck

Candy:

Try screwing the bolt in. Did you try the stop lever experiment? Can you get it to idle smooth at any rpm. I would still suspect the rack dampener if it does smooth out at some point. Mine would not idle smooth until I changed the dampener. Unless you have a new one to compare to it is hard to tell by just pushing in the spring. It appears to be critical if the spring has gotten weak. Keep trying I doubt if it is serious.
Cheers and Merry Christmas.

__________________
Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel

Mark,

I did try the stop lever experiment, and it was still the same rough idle. When I screw down on the dampener bolt, the idling smooths out around 1000rpm. Do you think it is a dampener problem? If so, I will purchase one. Also the sticker says the car should be idling around 750 rpm. Thank you and have a Merry Christmas!



Candy Verbeck

Merry Christmas Candy,

I had a similar problem with a 123 series diesel, and ended up running some diesel purge through the system. I suppose I had either one or two injectors that were probably dirty, giving a bad spray pattern, because it fixed the rough idle. Cost from parts shop $10.

Have a Great Holiday,


Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Candy:

Charles may have good idea with the diesel purge. If the stop lever trick did not change anything then it is not likely the rack dampener. You did do the adjustment with the engine warmed up?? You may have one or two injectors that have a poor spray pattern and at idle they may even misfire. To test that theory loosen each injector line at the injector with the engine running and notice for any change in the sound of the engine. If you come to one that there is no change then you have the problem injector.
I hope this rambling makes sense. Have fun and let us all know how it goes.

Merry Christmas

__________________
Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel

Mark,

I started out with one bad injector and then I replaced all my injectors with rebulit Bosch, and that still didnt slove the warm rough idling. Then I crack the lines at the injectors when it was idling rough, and that still wasnt it. I dont think it a injector problem. When the car is cold it runs very smoothly. But when it warms up, that is where I get the rough idling. I am thinking about buying a rack dampener pin, and hopefully that will slove the problem. That seems to be the cheapest alternative for now. Thank you for all your help and have a wonderful holiday!



Candy Verbeck

Candy:

Uhmm. Well I don't know what to suggest. Replacing the rack dampener can't hurt and it might just do it. Let us all know how it turns out.

__________________
Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel

Greetings Candy,

If the dampner adjusting bolt doesn't do the trick then look at a few other items or tests to help you to determine the problem. I assume you changed the injector to prechamber metal sealing rings when you replaced the injectors? Right?
I'd also take a stab at removing the vacuum line off the injector shut off valve located on the back of the injector pump after the engine is warmed up and idling rough, just to ensure there isn't any vac being slowly applied to it. Other possible ideas, like mentioned, don't assume a rebuilt injector is running clean fuel. It could be any of the fuel filters causing a blockage once the fuel has sloshed around in the tank. The injection timing may be off a tad as well as the start of delivery of fuel to the injectors. Excessive timing chain wear could also play a part as well as chain tensioner once the oil is warm. It's a process of elimination one by one to solve your problem.

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan