Normally I can work through these things but the logic of this pump and subsequent adjustments has me baffled. I need some help...

Background. My 240 blows clouds of smoke at 3200 feet and up. At sea level there is none. My conclusion is that the IP is delivering too much fuel at higher altitudes. (Sounds right I think)

So here we go.
There are three pics in this post. First is the IP diaphragm which is mounted on the back of the pump just in front of the throttle shaft and within this housing is a fitting which leads tot he banjo bolt on the intake manifold. Again logic tells me that this diaphragm in some sense measures the amount of vacuum created through the manifold, and compensates for the throttle position and in some small way altitude to pull on the rack within the IP to adjust the fuel flow.
If I pull this hose off the back of the pump the motor takes off! So this makes some sense to me...

The second picture is where the diaphragm attaches to the rack inside the pump. There is a minor adjustment to the compensating path here using spacers between the diaphragm and the attachment point to the rack... The adjustment on this is only 1.1 mm so I really don't know if this being off by say .01 mm would affect much but bear with me. On the left side of this photo is the attachment point for the bowden cable that shuts off the car. Now based on simple bowden cable theory it actually pushes on the lever which in relative terms pushes the rack to the back of the IP (picture view) to shutoff the flow of fuel hence killing the motor. I think I'm on this corrrectly... However the throttle as described below increases as it allows the rack to move backwards? I may have the shutoff theory backwards... Help...

The third picture in the series is the throttle housing which attaches to the back of the pump sandwiching the diaphragm between the main pump body and the throttle body. The throttle when engaged actually allows the rack to move towards the back of the pump as it is not directly connected but rather has a rotating point that is in contact with the center of the diaphragm and pushes it forward as the throttle is released or allows it to draw back as the throttle is depressed. What draws it back I have no clue. Vacuum? if so then why would the engine accelerate upon disconnecting the vacuum line? Wouldn't this in hteory allow the rack to move forward with no vacuum pulling on it? Now, in the third pic is a spring sticking up that has 5 shims under it within the throttle body and this spring mounts up against the diaphragm pushing on it constantly from teh back of the pump.

Okay, obviously I am totally confused on this subject. I believe that based on the smoking I need to reduce fuel at this altitude. But I cannot for the life of me figure out which adjustment I would make. Is it the shims under the spring (add or remove). Also I cannot seem to get the diaphragm to hold vacuum, partial yes but not "hold". I'm now beginning to think that it won't no matter since it is a leather like material.

I am open to a phone call at my expense if someone can help me figure this out...
Thanks, the perpetually baffled Fisherman

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Here is the diaphragm with a bolt inserted where it attaches to the rack.

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__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Here is the backend of the pump where the diaphragm attaches. there are no gaskets of any kind between the main body and the thortle body where the diaphragm is sandwiched. metal to metal is not real conducive to a tight fit that will hold vacuum.

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__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Note the spring sticking up. It pushes against the back of the diaphragm and has 5 shims of varying thickness under it within the throttle body so it pushes harder with the shims in place.

The rubber hose is the attachment point heading to the intake manifold and allows for a vacuum to be created within the throttle body essentailly pulling on the diaphragm (as far as I can figure out). remember earlier, removing this hose allows the motor to really rev immediately...

The throttle lever on the side of this assembly seems to allow the rack to move backwards (toward teh rear of the IP) during acceleration.

Attached Thumbnails

 

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

First you need a rearrangement of concept. The lever that is attached to the rear housing has nothing to do with fuel correction while driving. It is a dampener to deminish the rump, rump, rump at idle by touching on the rack somewhat.

Manifold vacuum is what balances the rack position against the spring tention all of which is shimmed in a couple ways. So when you open the vacuum line you do two things. First you add a huge source of air and second you send the mixture rich. The combination results in engine speed increase and a lot of smoke.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve, I missed that... how does he fix it ?

You don't. At full "throttle" that IP is mechanically forced open, I think, and it's gonna smoke because you are overfuelling it. No smoke if you let the vacuum governor do it's job, but no power, either.

Make sure the diaphram is in good condition (it probably is, because the engine speeds up when the vac is released, and try to avoid absolute full throttle use.

You can adjust it to not smoke at altitude, but it will then have low power at sea level. This can be done with the max fuel delivery adjustment, but I don't know where it is on this IP.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

ok,,, is your car a 115 body style ?

By 1977 they show an injection pump with automatic altitude correction... maybe you could put one of those on ... (?)
It also says that "accurate regulation and adjustment of injection pump is possible on an injection pump test bench only".
I hate those kinds of pronouncements.... but they say if you have that kind of bench the necessary data is available...

Do you have the 615 or 616 engine ?

I'm assuming this car doesn't have the infamous ALDA, but the vacuum line runs directly from the governor to the throttle body. Sometimes the "big picture" helps. Sorry about the terrible scan job. Remember that pushing the rack in (to front of car) increases the rate of fuel delivery, and that the spring and diaphragm are fighting for control. The spring/diaphragm assembly is the governor. Governors work on speed and load, and the mixing box/venturi control unit/throttle body downstream of the air cleaner decides which is more important. Your foot throttle moves the butterfly valve. The amount of vacuum created depends on the butterfly valve position and the speed of the air going through the air duct. High air speed and low load means the engine doesn't need much fuel. Another way to think of it is more vacuum created and the diaphragm wins the battle. At the other end of the spectrum is low engine speed and high load, which means low vacuum and the spring wins the battle and enriches the mixture. That's the theory.

There could be several reasons for the smoking:
1. Leaking diaphragm. I was surprised to see that my parts book indicated no gasket, so I'm now not entirely sure if the governor should be leak free, although my instinct tells me it should be. The acid test is power, smoking, and fuel mileage on the coast, providing the car lived its previous life at low altitude. Engine oil consumption may also be masking the issue.
2. Either a leaking or partially plugged vacuum line or fittings which may be inhibiting the maximum vacuum the governor sees and/or the governor's response speed.
3. Lugging the engine. I don't know if the car spends all of its time east of the Cascades or if you go back and forth. If back and forth and you're lugging on the big hills then it will take a bit of time for the carbon to be burned out.
4. Engine is not set up for high altitudes. This means those shims. Here you have to decide, based on where you drive. If it's all east of the Cascades then play with the shims so that the spring loses. It's a tough call if you go back and forth as a lean mixture at low altitude may result in a burnt piston.

My opinion: change the diaphragm as long as you have it apart. Doesn't make sense to me that it wouldn't hold vacuum, although I may be wrong here. Make sure you tighten the four mounting bolts in a decent pattern (think cylinder head). Then make sure you have no other leaks or obstructions in the line or fittings. Then try it. Remember you change the idle mixture at the throttle body, the running mixture with those shims. If it still smokes then decide whether or not to play with the shims. Just make sure you get the diphragm mounted to the rack properly. If that falls apart then the engine will run away.

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daBenz - 1970 220D

DaBenz:

That's the M type pump all right, but you left off the mechanical connection between the IP and the acelerator pedal. It mechanically forces the fuel rack to the full position, also, through some internal linkages.

Make sure the diaphram holds vac. It may or may not seal perfectly with the main body of the IP, but that isn't important unless fuel collects in the non-vac side of the chamber. It must seal with the cover, though.

Excess fuel in the main pump side can cause a number of problems, excess smoke is one of them. Also hard starts and poor governor control.

A quick and dirty way to reduce the smoke is to adjust for a lower no-load max speed as this will limit the linkage travel. It's the "wide open" screw on the venturi. Otherwise, you will need to reduce the maximum fuel rate on the IP itself. I will try to find the location over the next couple of days when thing quiet down a bit (company, family Xmas stuff, etc.).

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

OK, I'll state it again. The mechanical rod from the linkage to the pump has ABSOLUTELY NOTHING to do with the running down the road. ALL mixture is determined by the vacuum governor as in the picture.

The link running from the throttle linkage to the back of the pump is a dampener arrangement to stabilize the idle. IT DOES NOT need to be in place to run properly. If adjusted wrong it can only impare runnning.

These pumps had no ALDA altitude compensation as the vacuum governor should accomplish the same thing. You sound like you might be too rich overall which can be changed with shimming. Also be sure that the on/off lever is totally free of loading when in the "run" position. The cable end has an oval slot for the fuel lever. This is to allow enough movement in shut-off but no tention in run.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve, Can he put one of the later auto altitude compensating IP's on his car ?

Well that explains it. Been trying to see what the rod did to smoking also, all I could figure was it boost the rpms when set to drop down further at idle, and it turns out that's all it does. On mine the spring that pushes the lever back down was broken which would let the linkage and the lever align just right to lock at full rpms

How about we try to make sure we're all on the same page? This forum is here for us to help each other. I apologize for not using the correct MB language, as I learned this engine before I got the manuals.

First item of business is that gorilla knob. Cable from the knob to that oval "slot" connector. Push the gorilla knob all the way in means pushing the slot against the pin and shutting down the fuel or shutting down the engine. Pull the gorilla knob all the way out and the starter engages. The slot also pulls and holds the pin, which means the engine gets a little extra shot of fuel for starting. Release the gorilla knob and the pin floats in the slot. The adjustment here is to make sure all three events happen, meaning the pin gets pushed, pulled, and floats. If you can't get all three events to happen through normal adjustment then the cable is stretched and should be replaced.

Second item is the foot throttle/accelerator pedal. Pedal rotates the rod running along the firewall, the rod opens and closes the butterfly valve in the throttlebody/mixing box. A spring, external to the mixing box, closes the butterfly valve and lifts the foot throttle. There are no connections between the foot throttle and the IP, in this sense. Two adjusting screws at the throttle body. The first adjusting screw limits how far the butterfly valve can close (this also adjusts the amount of vacuum the governor sees). This is the low idle mixture screw. We perceive this as changing the low idle speed, but it's the mixture that dominates. The second screw is the no-load high rpm limit. Adjusting this will not appreciably change the mixture due to the high speed of the air in the air duct at high rpms. In other words, 200rpm change at 4000rpm isn't going to change the mixture enough to make a difference. I'm assuming here we're not abusing the engine in normal driving.

Third is that linkage running from the throttle body, over the top of the valve cover, then down and between the IP and the engine. This is the idle damper. Remember, at low idle the engine compression is just barely losing the battle with the crankshaft momentum created by combustion. If the idle mixture is set too rich then the engine will run without the idle damper. If the idle mixture is set too lean and the idle damper is taken away then the engine will sound like a Harley and die. This is because the rack wants to float at low idle, due to the rapidly changing vacuum in the throttle body, or pulsing. The air speed in the duct simply isn't fast enough to overcome the effects of the cylinder compression/expansion events at low idle. The idle damper prevents the extremes of the rack float. The adjustment is to set the low idle mixture too rich, disconnect the idle damper, lean out the low idle mixture until the engine stumbles, then turn up the low idle mixture a smidgen and reconnect the damper. Then road test to make sure the car can take off in low gear. daBenz is set up so that I can slowly let out the clutch in first gear and the engine doesn't stumble.

Fourth is the high idle knob. Fisherman's may be integral with the gorilla knob, daBenz has a separate knob. At any rate, what it does is override the low idle mixture screw by pretending it's the foot throttle. And nothing more. Adjust the cable to where you want, making sure it doesn't affect anything at low idle. I like a little slack at low idle, just to make sure.

Hope this helps. To me, this is the simplest engine control I've ever seen. After a lot of thinking and tinkering, that is. I fully understand Fisherman's confusion/frustration, and I admire his courage to dive into it.

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daBenz - 1970 220D

Just saw that I made a boo-boo in my first post. Should be: if you stay east of the Cascades then adjust the shims so that the spring loses. More vacuum effect at the governor means leaning the engine out. Sorry, I didn't mean to add to the confusion.

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daBenz - 1970 220D