My head is SPINNING
 

I have a 1983 Mercedes 240D with a 4spd, (manual). My engine has 24,000 original miles on it. It was purchased as a factory crate motor from MBNA and came complete with everything including the injection pump, etc...

Recently I have begun to notice that after my engine warms up, it idles poorly. Slightly revving the engine makes it worse. It shakes and misses terribly. However, above 1,400 RPM it runs smooth as silk.

I adjusted the valves to factory spec and replaced the fuel filters. No difference. The engine has plenty of power with no smoke. At highway speeds, engine appears to run perfectly.

One other observation, which happened by accident when a friend gave a 5 gallon jug of veggi oil to try in my benz, is that if I run thicker fuel, like vegetable oil, the problem completely goes away. but if I go back to diesel, the poor performace at low RPM comes back.

My conclusion is that my poor idle is the result of timing chain stretch which caused a slight change in IP timing, something I would have expected since the most chain stretch occurs within the first 20 to 30 thousand miles of an engine's life. I am guessing that the thicker fuel (vegetable oil) ignites more slowly than the diesel and my timing being off is compensated by the delayed ignition of the thicker fuel, (veggi oil).

So what I would like to do is test and adjust my injection pump timing. I did a search on IP pump timing and came up with all sorts of buzz words like "drip method", "well method", "milli volt", "RIV", "woodruff key", "RD bolt" and even "give the IP a slight bump toward the block"

What I would like to know is:

1. What is the best way to test my injection pump timing, (assuming I need to do this)
and
2. How do I go about adjusting the IP timing so it runs better on diesel? Is there a way to adjust the IP timing while the engine is running so I can get a feel for where my engine idles best? Can I do this, or is not advisable?

I really appreciate your help and advice. You guys are great! Thanks!

Have you considered the possibility of an air leak into the fuel system? Does it run any better on an alternative fuel source such as is used during a purge?

You should have ZERO chain stretch at 24,000 miles.

Have you done a diesel purge yet? Also, have you checked for an air leak? Fuel lines will still dry rot over the years.

My car has about 4 degrees of chainstretch at 237,000 miles. I'll be replacing the chain at 250,000 instead of using a woodruff key.

Kerry Edwards,

If I had an air leak, I would assume I would see air bubbles or a low fuel level in the pre filter, (my pre filter is clear), but I do not. It is full with diesel - no air and no air bubbles.

When you say a purge fuel, do you mean something like diesel kleen or some other fuel injector cleaner? No I have not. Do you think my problem is caused by dirty injectors? If so, wouldn't a dirty injector perform worse on a thicker fuel like veggi oil?

I was referring to the procedure used when purging, which involves putting fuel in a bottle and attaching it to the primary filter, and putting the return line into the bottle also, thereby bypassing the fuel tank and fuel hoses upstream of the filter. Using this system would rule out any fuel delivery problems from the primary filter back to the tank.

rrgrassi,

I was told that the majority of chain stretch occurs in the first 20 to 30K miles. Is that incorrect?

To the best of my knowledge my fuel lines are original, but they appear good.

Everyone seems to recommend a diesel purge. I drive my 240D to work every day and it's a 90 mile round trip. Most of these miles are a constant 80+MPH, which in a 240D is about 4,000RPM, so I assumed my injectors and conmustion chambers are pretty clean.

kerry edwards,

When I "purge" in this method, do I use a special fuel, or just plain diesel?

Also, assuming I wanted to experiment with my IP timing, how do I do this? Is there a good thread someone could suggest?

People use diesel purge to clean their injectors with this method but all you need is some kind of fuel, diesel is fine. I wouldn't be considering timing issues or chain stretch until other things are ruled out. It's unlikely that the timing has changed or the chain stretched so I'd put those hypotheses way down on the 'to test' list.
Have you replaced the air filter?

It sounds to me like you have an injector problem. With your engine idling crack each of the injector lines one at a time. Each one should change the idle the same amount. If one changes/decreases the idle less than the others that injector isn't working right. There are multiple options for repairing... the easiest is to take it to a Bosch shop to get the injector tested and repaired.

The Diesel Purge is an actual product name. Its made by LubroMoly (I think thats the correct spelling). You put about two cans in a jar and disconnect the fuel supply and return lines. Put both of them in the can and run off of straight diesel purge. This is supposed to clean the injectors, but it doesn't work for everyone (myself included). For some people it works wonders though!

The 'proper' method of timing your injection pump is to use the drip method. If you have a Factory Service Manual CD (if you don't they're $20 and are very much worth every penny!) you can find the procedure there. Should also be able to find it on the forum somewhere too. It does require a $20 dollar tool or you can make one yourself.

Hope that helps! :)

Tymbrymi,

I will pick up a couple of cans this Diesel Purge this weekend and see if that helps.

I assume the idea is to run the engine on straight "diesel purge" until all of it is used up and then reconnect the hoses back to the stock fuel system? I assume it will take a while to burn up 2 cans of this stuff.

One question still lingers though....if the miss at low RPM were caused by a dirty injector(s), why does it run fine on a thicker oil but runs worse on a thinner oil? Wouldn't a thinner fuel spray better from the injector? Also, this problem only occurs when the engine warms up. When the engine is cold, it idles fine. :confused:

not to highjack the thread but by curiosity:

How much money did you pay for a crate OM616 ?

I am watching this one closely. Mine starts up smooth as silk. 10 seconds it starts to stumble. Runs great on the road. shacks like crazy at the ligth after a highway run.

You got it! :cool: One thing that helps is to change the RPMs a bunch while you're doing it. Helps the fuel go faster and helps clean the injectors more. Hope it works out for you!

The thickness of the oil has nothing to do with it. WVO has slightly different combustion characteristics. I think it combusts slower than diesel... Either way it is known for quieting and smoothing out diesels.

Not sure on the hot/cold thing... hopefully others will chime in!

You have a 617 turbo? Do a search on 'rack damper bolt' or similar. If it literally rocks the car it is probably that... that bolt is designed to dampen an oscillation in the IP, and has been replaced with a newer bolt that has a stiffer spring in it. If you're lucky you could still have some adjustment left in the one you have now. :)

That I have not heard. I do know they would stretch a little, but 4 degrees seems like a lot for only 24,000 miles.

How long has the car sat before you got a hold of it? Did you check the tank strainer? A diesel purge using the lubro moly stuff, or some sea foam helps to clean out any build up or deposits left by the fuel that sat so long before you got the car. Also check the tank venting. A vacuum in the tank can also cause poor fuel delivery after a few minutes of running. Diesels really need to be driven, and your 90 mile round trip is actually good for that.