IP running full open on 74 240d - PeachParts Mercedes-Benz Forum

wildhorsemfg · #1 10-20-2012, 03:42 PM

after looking through the IP help link posts i cant seem to find this problem ..
I have a 74 240D w115-114 w/ 4 speed manual , currently removing the engine to rebuild it . because it has ultra low compression . like 140lbs

But when it was running it would blow horrible white smoke ,
and it seems the IP is running full open all the time .
the throttle plate seems to be limiting the cars RPMs , like in a gas engine .
but i disconnected the control rod to the ip and pulling it up and down make no difference how the engine runs
...
does anyone know what is causing this or and advise on how to take apart that back 1/2 of the Ip ?

as stated i am doing a full rebuild so it will be all apart this week .. but Ips are kinda something i dont know much about the internals .

Diesel911 · #2 10-20-2012, 04:53 PM

It is not the only possible cause of the problem but you could be dealing with a 38 year old Governor Diaphragm that I have been told is made of oiled Goatskin.

Since when the Throttle Valve is closed there is a high intake Vacuum and that is at idle the Governor must reduce the Fuel in the presense of a High Vacuum.
With the Throttle Valve open there is a low Vacuum and the Fuel Injection Pump gives more Fuel.

To Me that suggests that there is a hole or rip in the Governor Diaphragm or the Diaphragm has become stiff and is not reponding to the Vacuum.

There is also other parts of the Governor Housing that can leak Vacuum when worn and there is an area of the IP that is esposed to Atmospheric pressure; I believe by way of the Oil Fill Cap.
If that Cap is plugged with dirt it would trap or restrict the Air on one side of the Diaphragm and the Diaphragm is not going to work properly.

I don't know much about these pumps but I think there is a Fuel enrichment position for starting. If that part of the pump is stuck you will get too much Fuel.

The manual has a proceedrue for replacing the Diaphragm. However, in the Center of the Diaphragm there is a tube with a Hole in it that a Pin in the IP passes through. When you remove the Diaphragm from that pin you need to be cautious because there is a spring and Shims in side.
Those parts need to go back into the same place on the new Diaphragm.

Govert · #3 10-20-2012, 06:14 PM

The governor doesn't work on the intake manifold vacuum, but on the vacuum created by means of a venturi below the air valve. The air valve determines the air flowing through the venturi.

The rod doesn't control the IP, but only the poppet cam of the auxiliary mechanical governor.

My guess is that you have disconnected the air hose, but the diaphragm might be torn too. The control rod inside the IP can be stuck too.

Below is a recent write-up I did in a similar topic on Benzworld about the pneumatic governor, which might give you insight in how it works. Do read the more elaborate topic and the FSM if you want to know more. If you are going to overhaul the governor, you have to follow all the steps in the FSM.

The fuel enrichment is only done by means of the starter knob, when you pull the knob during starting, it pulls the control rod of the IP in the starting position, i.e. even more than full load.

{quote}
the injection pump has a so-called pneumatic governor. The governor is responsible for the amount of diesel injected into the engine, that determines (together with the load on the engine) the speed of the engine. It is very easy for diesel engines to overspeed, that is why there is a governor. The governor makes it possible for the engine to idle at a constant low speed and not to overspeed (more than 4400-5400 rpm).

The pneumatic governor works by means of a vacuum created by a venturi in the intake manifold. A butterfly air valve (see picture below) determines the amount of air flowing through the venturi, i.e. more of less vacuum. The valve is controlled by your foot pressing on the accelerator pedal. The vacuum is "transfered" to the vacuum chamber of governor by means of an air hose. That is why there is an air hose running from the intake manifold to your IP.

Butterfly air valve in the intake manifold with venturi at the bottom.

The amount of diesel injected into the engine (and therefore the speed of the engine) is controlled by the control rod. The control rod is connected to a diaphragm. A spring pushes against the diaphragm, so that the control rod is pushed into the maximum position. The vacuum works on the diaphragm, so that it is pulled back against the spring pressure (in fact the air pressure on the other side of the diaphragm pushes against the diaphragm). So the variable vacuum created by the venturi in the intake manifold determines the amount of diesel injected.

This system works for the higher speeds of the engine, but at lower speeds and at idle the engine will fluctuate in speed ("sawing" of the engine). Therefore an auxilliary mechanical governor is installed, so that the control rod rests against a spring stop. That mechanical governor is brought into action by a rod, running from the intake manifold, over the valve cover and to the side of the IP. The rod turns a poppet cam into position. When the accelerator pedal is pressed deep enough, the poppet cam moves away and the governor purely works on vacuum.

Picture of a IP, red dot is the poppet cam axle, blue dot the air hose, green dot where the diaphragm is (on the inside)

Diagram of the governor

8 = control rod
10 = diaphragm
13 = spring
15a 15b = poppet cam

If there is an air leakage, for instance a loose air hose, torn diaphragm, leaking axle of the poppet cam, the idle will be high, because there will not be enough vacuum to pull back the diaphragm, and because the air valve will be closed, there will not be enough air to burn all the diesel, so that the engine smokes.

So you must determine where the air leak is. If you read this topic:
White Smoke 220D - Benzworld.org - Mercedes-Benz Discussion Forum
you can find out how the system works and how to diagnose it. After that you only have to find the parts...
{end quote}

Source: 1973 220D W115 Injection Pump Gasket - Benzworld.org - Mercedes-Benz Discussion Forum

Here you can see the diaphragm (on a slightly older MB diesel engine) when the rest of the governor is removed:

The spring presses against the middle part, the leathery part can tear.

Diesel911 · #4 10-20-2012, 07:55 PM

Thanks, Govert.

I think I remember reading of at least 3 Members changing out the Governor Daphragm. There may be some threads below.
Also at least 2 persons have said the Diaphragm is cheaper from the Dealer then if you buy it from a Bosch Fuel Injection Shop. But, see if you can locate who said that in the threads.

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wildhorsemfg · #5 10-21-2012, 12:21 AM

thanks . i will post some pics once it is taken apart .
So can the back half of the Ip be swapped with a newer one that doesn't use that intake line ?
or is the whole Ip different ?
i would prefer to do away with the whole butterfly vale and use newer (79) manifolds

Robert Williams · #6 10-21-2012, 12:53 AM

I wonder if there might be some connection between the low compression and the appearance that the IP is faulty somehow?

Might it be that the low compression is a piston ring issue (if the engine had sat for a long time and the rings have seized in the lands as they are known to do) that also might contribute to the engine sucking crankcase oil up past the seized rings ala` a "run away" engine? That is why the air valve can be used to effectively throttle the engine, it might explain the massive smoke issue also.

Might be worth holding off delving into the IP and first try to get a look at if there is some other factor that could contribute to or even precipitate this set of symptoms, if you're diving into the engine anyway it should be pretty clear what's going on with the compression and that might have a bearing on the broader situation.

Govert · #7 10-21-2012, 03:43 AM

Quote:

Originally Posted by wildhorsemfg

thanks . i will post some pics once it is taken apart .
So can the back half of the Ip be swapped with a newer one that doesn't use that intake line ?
or is the whole Ip different ?
i would prefer to do away with the whole butterfly vale and use newer (79) manifolds

I suppose it is possible in theory to put a mechanical governor on the back of your IP, but it would require recalibration by a diesel workshop. And you have to find a mechanical governor that fits, not easy either.

You could install a later IP which has a mechanical governor, but oil supply might be a problem. Your present IP has its own oil supply, later ones were included in the engine oil circuit. The later MW-style IP had the oil supplied via a seperate oil line, the MRSF-style pump had the oil supplied via the camshaft. The intermediate shaft inside the engine was also different to give oil to the IP. So a MW pump can possibly work.

But if you overhaul the pneumatic governor, it will be good for twenty years or so.

wildhorsemfg · #8 10-21-2012, 10:57 AM

yes the engine has sat for a long time , last plated in 98 , so not sure if started after then .