I consider myself a fair DIY mechanic, but I wish someone would explain to me how a 617 IP throttles. I understand that the IP is basically a small version of the engine with cyllinders and pistons to push fuel into injection lines, thus past the injectors. How does the IP change fuel volumes to the injectors to increase or decrease power? Does the piston stroke remain the same? Does it change? How can the fuel volume change if the piston displacement does not change? I have a spare IP to tinker with.
Thanks

It is hard to describe how it is done in words. If you had the parts in your hand it would be easier to understand.
Also not all Fuel Injection Pumps use the same means to change the Injected Fuel quantity. So, I will try to describe the Mercedes IP.

First picture a solid Plunger in side of a Cylinder (Mercedes calls this an Element I am used to calling it a Plunger and Barrel). At the open end of the Cylinder is a spring loaded Valve (I call it the Delivery Valve). Somewhere below the top of the Cylinder is a hole to allow the Fuel to come in (Fuel Feed Hole).

So the Plunger comes down and exposes the Fuel Feed Hole and the Fuel goes inside (due to the Fuel Supply/Lift Pump providing the pressure and volume). The Deliver Valve has enough spring tension to keep it from opening.
The IP Camshaft pushes the Plunger up closing the Fuel Feed Hole and pushes the Fuel past the Delivery Valve into the Fuel Injector Hard Lines and when the pressure is high enough to over come the Opening/Pop Pressure of the Injectors the Fuel is Injected into the Engine.
The plunger always has a constant stroke (also the Barrel always remains stationary).
So now we have a constant amout of Fuel being Injected and no way to shut the Fuel Off.
So we cut a Vertical Slot partially along the upper portion of the Plunger. Now if we rotate the Plunger so that the Slot is in alinment with the Fuel Feed Hole as the plunger goes up and down it just pushes the Fuel In and out. So now we have a way to shut off the IP by rotating the Plunger.
So now comes the part that is hard to describe. Now we are going to make another cut in the Plunger. We are going to start with that Slot we made to shut off the IP except that we are going to move down the slot a little before we start the cut.
So we move down the Slot a little and we start a cut at lets say a 35 degree angle going down and at the same time partially around the plunger. This angled cut is called a Helix. See Attached pic. Green Arrow points to the Shutoff Slot and the 2nd Red Arrows points to the Helix. (There is no Fuel Feed Hole shown in the pic.)

So now when the plunger is going up and down and we rotate the Plunger past the Shutoff Slot a portion of the Plunger will cover the Fuel Feed Hole until it reaches the Bottom of the Helix; at that point the Fuel Feed Hole is exposed to the empty space under the Helix that is connected to the Shut Off Slot and Fuel Stops being Injected.

In pic 2 if the Fuel Feed Hole is exposed to any area inside of the Green outlined areas there will be no fuel Injected.
If the Plunger is rotated and Feed Hole is covered by the Red Arrowed Area that would be your idle Fuel quantity.
If the Plunger is rotated more and the Feed Hole is covered by the area with the Light Brown Arrow that would be approximately the Maximum Fuel that could be Injected.

Attached Thumbnails

   

__________________
84 300D, 82 Volvo 244Gl Diesel

The 2nd part of how the Fuel is controled is that the bottom of the Plunger is connected to a Gear. The Gear is connected to a toothed Rack, like Rack and Pinion Steering except that in this case the Rack turns the Pinion/Gear. This is what rotates the Plunger into the various positions to give different amounts of fuel.

The Rack is hooked to the Governor. In general while the Gvernor is spinning the Governor weights want to move the Rack to shutt off the Fuel. But, there is a Governor Spring there.
(This is a simple generic explination of how the Governors in genral works. There is a detailed exlpination of how the Merceded Governor works in the Service Manual.)

What you do when you step on the Accelerator Pedal is you are compressing the Governor spring. Compressing the Governor Spring pushes the Rack in the more Fuel direction. As the Engine speed increases the Governor Weights swing out increasing their counter force on the Governor Spring and if you foot is held in one position they balance with Spring Compression and your Engine will not accelerate any more.

The Vaccum Shutooff pushes the Rack into the Shutoof position.

__________________
84 300D, 82 Volvo 244Gl Diesel

Diesel911- thanks so much for the explanation- now it makes more sense to me. I took the delivery valves and some of the plungers out of my "tinkering" IP to try and make sense of it. Now I'll go back for a closer look. So, when a shop tears down and rebuilds a pump, I suppose all those plungers must line up on some mark to deliver equal amounts of fuel as they rotate with throttle changes- in essence kind of a static timing?

Diesel911 has done a great job once again at a very difficult topic.

The purpose of the fuel injection pump is to deliver an exact metered amount of fuel, under high pressure, at the right time to the injector. An inline pump has one plunger for each cylinder. It is the reciprocating up/down motion of the plunger that performs the high pressure pumping, while the rotation by the rack is responsible for the metering to each cylinder.

The rack is connected at the same angular rotational position on each plunger. Thus the metered amount of fuel delivered from each of the elements to each cylinder is identical since each plunger is machined the same. It is in this way that by moving the rack one effectively changes the point in the helix when the spill port opens. This type of pump is classified as an 'In-Line, Constant Stroke, Variable Volume Injection Pump'.

Some more terms.
Start of Delivery: When the fuel Feed Port is closed by the rising plunger. This is when the fuel begins to become compressed and pressure begins to build.

End of Delivery: When the Spill Port is exposed by the rising helix channel. This is when the pressure falls back to zero and the Delivery Valve will close.

If you wind up with a disassembled pump or a spare pump (working or not)and you are about to throw it out.....please do not. I will pay you to ship it to me and I will make a photolog (new word??) of how to tear down and reassemble an IP for this great forum. It will include how to evaluate what needs replacement and where to find the rebuild parts. I do not have a scrap pump however so I am unable to do it now.

__________________
Dionysius

Bravo!!

This was a bad idea unless the IP was no good. If it was an IP like mine and uses the Plunger And Barrel/Element like the first Pic. and you did not mark the exactly where they were positioned you may not get them back in the right position to where the put out the amout of fuel the were set at.

On the other style of pump in the 2nd picture item #23 is the Plunger and Barrel/Element. On that one there is an alinement pin inside of the bore it goes into in the IP housing and a Slot on the side of the Barrel that the pin fits into.

On both of the Plunger and Barrels it is possible to get the Plunger rotated 180 degree out of position.

After an IP is rebuilt it goes on the test stand. One of the things you do in the test stand is you set the Fuel quanitiy at Idle and at Full Load. You adjust each Element individually. There is no line that you line up and get the Fuel quanity that you are supposed to get. This is why just about no one recommends removing the Elements. Especially on the one like in the first pic.

Attached Thumbnails

   

__________________
84 300D, 82 Volvo 244Gl Diesel

The IP I took apart is one destined for the pump shop- so I felt pretty safe turning it into my learning tool. Thanks for all the excellent posts. My knowledge just increased significantly, though my experience still lags.

Correction- I took out some of the barrels instead of the plungers. The plungers were fixed in place. I think I just realized something... I noticed the barrels are adjustable- in other words, they could be rotated a slight bit. I suppose this adjustment is used when the injection shop dials in the proper volumes to balance the pump.

Adumars: Since these are precision machined items all matched parts have to be kept together and the orientations maintained to preserve all wear patterns. Any obvious scratches on these faces should call for replacement of those mating items. I am at a loss to understand what you mean by 'the barrels are adjustable'. Perhaps you can explain this more to me.

__________________
Dionysius

I'm thinking I'm using the correct nomenclature and this is in reference to a 617 pump only- The delivery valve threads onto the barrel. The barrel slides down into the pump body over the plunger and is attached via a flange with slotted holes that slides onto studs. It appears that the slots allow for some rotational adjustment, which would allow rotation of the barrel (and the fuel feed hole), thus affecting its orientation to the helical port on the plunger.

Diesel911 and you have given an excellent description of how an injection pump throttles, which was the original question. So, the last post was posing an additional question "does rotation of the barrels" allow the pump shop to dial in the proper fuel volumes to balance the pump output.
Excellent discussion- thank you both for the education.

very VERY usefull info, thanks guys!!!

__________________
93 b2200 EFI turbo, reg cab/short box, F2t swap build thread here
92 B2600i Cab plus getting a 82 3.0L 5cyl 617 mercedes Turbo Diesel build thread here
96 GMC 1500 z71 4x4 6.5L turbo diesel
Diesel all the way!!!

If the Barrel looks like the first picture in my post #7 you are correct the barrel is rotated to adjust the Fuel. The Shim/s that are under the Barrel ajust the timing of the barrel to the IP Camshaft.

The Barrel in the 2nd pic (item #23 Element) remains stationary in the IP housing at all times and the fuel is adjusted by Rotating the plunger.
The T shaped bottompart of the Plunger fits into item #26.
The tab on item #26 fits into a channel that is attached to a Square rod (the Rack). In order to adjust the Fuel quantity for each Element you loosen the locking screw on the Channel and slide in down the Rack and tighten the locking screw. This Rotates the Plunger.

Other types that use Item #23 type Elements have a item #26 that has no tab but has a Gear Toothed Ring with a locking screw that goes around #26 and the Rack itself has teeth. In order to adjust the fuel you loosen the locking ring and rotate the Gear Toothed Ring.

The exasparating part is that moving those adjusting parts a little bit cause a big change in the Fuel Quanity. Just like the Injectors all the Elements are supposed to be balanced as to the Fuel Quantity they put out.

__________________
84 300D, 82 Volvo 244Gl Diesel

Diesel911 this is sounding very familiar .

Ask me how I know. I've had so many runaways that my nerves are shot now. No wonder the folks that know how these things work never say anything.

BenzDiesel