240D Linkage question - PeachParts Mercedes-Benz Forum

zenuff · #1 06-19-2010, 12:45 PM

Hello. I would like to know what the linkage that crosses over the top of the valve cover on my 79' 240D does. I have three pieces one goes to the injection pump and the one crosses over the top and hooks to a long rod that goes down on the air intake side of the engine. I assume it is controlling air in take while the one on the injection side is controlling fuel.

Is there a balance to these? Like on a gasoline car, air fuel mix.

Stevo · #2 06-19-2010, 02:37 PM

If I remember right, after the rod goes down behind the air filter it pivots and connects to a horizontal rod that connects to the bell crank on the fire wall then to your accelerator pedal.

toomany MBZ · #3 06-19-2010, 02:45 PM

I also think it's an accelerator pedal linkage.
Do you have an automatic or manual transmission?
Diesels do have an air fuel mix, it may not be adjustable on non turbos.
The pics may help.

JEBalles · #4 06-19-2010, 03:07 PM

Quote:

Originally Posted by toomany MBZ

I also think it's an accelerator pedal linkage.
Do you have an automatic or manual transmission?
Diesels do have an air fuel mix, it may not be adjustable on non turbos.
The pics may help.

The accelerator pedal linkage that controls the injection pump does not go over the valve cover. There is another linkage attached to that linkage that goes the the black box and, on my 4-speed manual, went to a linkage that controlled a butterfly valve inside the intake. Every linkage on the manifold side of the engine has to do with emissions control, which someone must have, ahem, stolen off of my engine.

And diesels do not have an air-fuel mixture outside of the combustion chamber like most gasoline engines do.

JimSmith · #5 06-19-2010, 04:56 PM

The intake butterfly valve is an idle control feature. Once you are off idle the butterfly valve is open. As far as I know the only emissions related feature on those cars is the exhaust gas recirculation line, which I believe is controlled by vacuum - applied to the black box on top of the valve cover and through that device applied as needed to the valve controlling amount of exhaust gasses that get recirculated. Jim

zenuff · #6 06-20-2010, 01:59 PM

I was trying to figure out the best way to adjust this top linkage back to were it's supposed to be, it was loose when I got the car. I figure if one side is controlling fuel and one side is doing the air then their must be a balance between them for optimum burning of the mix.
But I may still be drawing parralells with gasoline engines.

soothappens · #7 06-20-2010, 02:11 PM

My 78' goes over the valve cover but it goes to a bell crank as Stevo said.
Manual 4 spd.

JEBalles · #8 06-20-2010, 03:34 PM

Quote:

Originally Posted by zenuff

I was trying to figure out the best way to adjust this top linkage back to were it's supposed to be, it was loose when I got the car. I figure if one side is controlling fuel and one side is doing the air then their must be a balance between them for optimum burning of the mix.
But I may still be drawing parralells with gasoline engines.

You still are. Diesels burn lean, you do not get more power from a stoichiometric mix like you do with spark-ignition engines. The injection pump is limited so that at max setting, it is injecting a stoichiometric amount of fuel to react with the oxygen in the air at whatever elevation you're at.

Jim has clearly been doing this for much longer than I have, put I'm thinking theoretically here: how would restricting the air passage help control idle? I'm nearly positive that diesels are only controlled by the amount of fuel injected.

JimSmith · #9 06-20-2010, 04:19 PM

One of the manuals has a chapter on setting the butterfly valve. Basically it is intended only to come into play during idle. Check the linkages - they have slots and slop in them to allow the air flow through the butterfly valve to keep it open wide if the throttle is off the idle position. At the idle position the linkage closes the valve - which is not closed all the way (there is a stop to adjust the valve's "closed" position).

I believe the intent is to provide a safe and repeatable idle for hundreds of thousands of miles of use. I do not believe the idea is to control mixture to achieve an ideal air and fuel mixture. If you notice when you step on the throttle, there is a bit of resistance and lack of response, and then the response is more of what you experience when driving. The butterfly valve is not open until you stop feeling that resistance or lack of response.

The no load demand for fuel is very low for a Diesel. Since engine oil and blow by products are fuels to a Diesel, the idle speed is tough to actually control as the amount of fuel needed is very small and over the life of the machine the degree to which other sources of "fuel" are added outside the throttle system increases. So, by limiting the air flow to that necessary to support the idle speed regardless of the fuel source you get a well controlled idle for the life of the car.

Hope this helps.

Jim

toomany MBZ · #10 06-20-2010, 05:20 PM

http://www.peachparts.com/shopforum/showthread.php?t=277670

There's a pic of the intake minus the butterfly valve in the above thread, a manual transmission, what is in your car?
No, there isn't a mixture there, sorry to mislead. To obtain an explosion you need air and fuel to mix in the presence of high enough temperature, compression provides the heat.
If you can get a FSM, the procedure to adjust the linkage should be in it.

JEBalles · #11 06-20-2010, 09:47 PM

Quote:

Originally Posted by JimSmith

One of the manuals has a chapter on setting the butterfly valve. Basically it is intended only to come into play during idle. Check the linkages - they have slots and slop in them to allow the air flow through the butterfly valve to keep it open wide if the throttle is off the idle position. At the idle position the linkage closes the valve - which is not closed all the way (there is a stop to adjust the valve's "closed" position).

I believe the intent is to provide a safe and repeatable idle for hundreds of thousands of miles of use. I do not believe the idea is to control mixture to achieve an ideal air and fuel mixture. If you notice when you step on the throttle, there is a bit of resistance and lack of response, and then the response is more of what you experience when driving. The butterfly valve is not open until you stop feeling that resistance or lack of response.

The no load demand for fuel is very low for a Diesel. Since engine oil and blow by products are fuels to a Diesel, the idle speed is tough to actually control as the amount of fuel needed is very small and over the life of the machine the degree to which other sources of "fuel" are added outside the throttle system increases. So, by limiting the air flow to that necessary to support the idle speed regardless of the fuel source you get a well controlled idle for the life of the car.

Hope this helps.

Jim

Yep, thought I could be wrong. Although, can you explain why (if I recall correctly) the euros don't have any linkage that goes over the valve cover. Maybe they just don't have black box, I can't really remember.

Anyhoo, I removed the linkage and valve and I haven't noticed a difference.

JimSmith · #12 06-20-2010, 10:30 PM

Euros have no emissions system meaning no EGR valve. The black box has a vacuum line to control the EGR valve, and gets some kind of input from the throttle. So, the linkage over the top of the valve cover is simpler, or, in some instances it may not go over the top (I don't recall the W114/115 arrangement off the top of my head, for example).

So, no butterfly valve sounds a bit risky to me - I get the impression it is a safety (mostly machine, but could be for life and limb in some instances) feature/system.

Jim

aaa · #13 06-20-2010, 10:46 PM

I don't remember other nonturbos (300d) having it. The other purpose it has is for the EGR, close the flap a little to generate a small vacuum and suck in exhaust gas for EGR.

zenuff · #14 06-21-2010, 12:22 AM

I don't see a black box on top of my valve cover just the two bolts holding the levers for the linkage and it's were the cruise control cable and throttle speed cable hook up. I lengthen the rod a little and seems to shift smoother and more in the appropriate rpm range. Maybe giving more vaccum if the trans hookes up to the manifold. This is my theory at the moment as I'm still doing research.
Btw my car is a auto.

I'm wondering if this car is a euro model because of the missing black black box.

Thanks for all the input.

JimSmith · #15 06-21-2010, 12:56 AM

The emissions regulations for 1979 models was likely not the same as applied to 1982 and 1983 model 240Ds. I have had both of the latter years and a 1975. I don't recall the 1975 having any EGR hardware at all. Before that I had a 1971 220D. It was also without the "benefit" of an EGR system. So, it is possible the stock US model in 1979 had either no EGR valve or just a different actuator.

Both the 1971 and 1975 model Diesels had an intake butterfly valve, but the actuation mechanism was different than the 1982 and 1983 240Ds.

Jim