I wanted to make this a separate thread from the long one about my fixing Brian Ach's rust-contaminated tii to make it easier for other folks to find the pertinent information without having to look through pages and pages.
Pursuant to the other thread, I was trying to nail down a rough running problem in a tii. It eventually turned out to be four rusty injectors, one of which was internally broken, but before I knew that, I convinced myself that rust in the fuel had created a "stuck piston" inside the Kugelfischer injection pump, without really even fully understanding what that meant. There are a few threads that describe the phenomenon, and one that says "it's not really that big of a deal to pull the head off." So I did.
I learned so much. Let me try to boil it down and serve it up.
Read the Tii Manual, But the Cutaway Photos are Misleading
If you have a tii and haven't read "The BMW 2002 tii Fuel Injection System" by BMW of North America (http://www.2002tii.org/pump/pump_guide_v1.pdf) cover to cover, just stop right now and do it. It's an excellent resource. However, it relies, perhaps overly, on those funny cutaway diagrams. The manual essentially says "there are no user serviceable parts inside the pump," so they don't say a word about unbolting the head. Because of this, the manual shows you no photographs whatsoever of the stand-alone head or the pump with the head off, and yet it shows you these odd cutaway views that are a little misleading because, obviously, when you open it up, it doesn't look like that.
So here's two pics of the pump with the head off, first with the pushrods exposed (this will be explained more below):
and then with the pushrods partially obscured:
And here's a pic of the top of just the bare head. The four holes down the middle are where the four suction valves and the Allen key caps on top of them normally go. The two sets of two offset holes outside these are where the delivery valves normally go. The injection lines screw onto the tops of the delivery valves.
and the underside, where you can clearly see the bores (cylinders) that the plungers (pistons) run in:
The Kugelfischer Pump Is and Is Not Like a Little Engine (engines don't have pistons IN THE HEAD!)
The manual says "The injection pump is Kugelfischer Model PL 0 Mini Pump. Its interior is very much like a small engine." Well, it is and it isn't, and we'll get into that.
The description in the manual of the basics of fuel delivery is quite concise:
"There is a camshaft which drives tappets. These, in turn, drive plungers which are pushed back down by springs. When these plungers move down, suction valves are pulled open and gas is sucked into the cylinders of the pump. Pressure created by the upward stroke of the plungers forces the suction valves closed and the delivery valves open. Fuel is pushed out into the delivery lines and through the injectors. The pressure generated by the injection pump is quite high -- 35 to 38 bar."
And that is really all that you need to know about fuel delivery, which is all I was concerned about. The rest of the action that goes on in the bottom part of the pump has to do with enriching, fuel timing, warmup, and other things.
But here's what it doesn't say, and what you only learn when you pull the head off:
--There's some truth to the analogy that the pump is "very much like a small engine" because the description talks about a "camshaft" and "tappets" and "cylinders" and "plungers" (note it doesn't say "pistons"), and it does have those pieces.
--However, the analogy falls flat because there isn't really a block, the "camshaft" and "tappets" are in the bottom part of the pump, and the cylinders are in the head, which is all topsy-turvy from the "little engine" image.
How Fuel Delivery Works (the head is pretty dumb, and they're spring-loaded plungers, not pistons)
--The manual refers to plungers, but many people refer to them as pistons. And since they run in the little cylinders, people think of them as pistons. But they're not rigidly connected to the camshaft. There aren't little connecting rods and wrist pins or anything. The little pushrods ("tappets") shown in those first two photos of the bottom end of the pump go up and down, and push on the bottoms of the spring-loaded plungers. The tops of the spring-loaded plungers go into the cylinders on the undersides of the head. The springs cause the plungers to retract from the underside of the head.
Here are the little spring-loaded plungers. Each is about half the length of my pinkie:
And here are the plungers sitting in the head (the whole assembly is, obviously, sitting upside down):
--Other than the plungers going up and down, the head is really quite dumb. It's really just passageways.
--The suction valves sit on top of the plungers under those little Allen key caps. You can undo the caps and pull the suction valves out with fine tweezers (NEVER USE A MAGNET) and see the tops of the plungers. You can then push down on the tops of the plungers with something non-marring and the plungers will just bounce on their springs. Again, they're not rigidly attached.
Here's a photo looking down into the holes where the suction valves sit. They've been removed, so you can clearly see the tops of the plungers. The delivery valves are out as well so you can look into their little threaded chambers, but unfortunately you can't see the passageways.
--Fuel enters the head at the banjo bolt at the front (not shown above; not installed) and leaves at the pressure regulating valve at the back (shown above on the back -- right -- side of the head). In between, it's just a straight shot. Except, as the description says, if a plunger is drawing downward, the suction valve allows fuel to be drawn into that cylinder.
--As the plunger goes upward, the fuel is put under pressure, and is squirted out a passageway in the side of the cylinder wall. That's right -- fuel comes in at the top but is squirted out the side. Rather unlike a little engine, huh? The passageway goes to the small threaded chamber that the delivery valve for that cylinder is screwed into.
--If you do what I did (and, seriously, don't do this) and remove one of the delivery valves and run the fuel pump just to make sure the passageway is clear, fuel will shoot quite spectacularly (clear across the garage, in fact) out of the passage in the threaded delivery valve chamber at about a 45 degree angle..
Why Rusty Fuel Can't Contaminate the Rest of the Pump
--Again, the bottom end is where the mechanical smarts are. The head is really kind of dumb, just passageways. Fuel comes in the front, some of is squirted out the delivery valves, but most of it flows out the back of the head at the pressure regulator valve.
--As per the other long thread about Brian's car, I can't comment on how rusty gas got into the injectors, because I don't know. I also can't say for sure whether, if rusty gas inundates the pump head, if it should be expected to pass through the suction valves, the passageways in the head, the delivery valves, and train-wreck at the injectors. But I can say that rust or other contaminants in gas really have no way I can see to get into the bottom Swiss watch part of the pump.
--And it is very straightforward to pull off the pump head and just blow the passageways out with carb cleaner and compressed air just to be certain they're clean (which is what I did when I had it off).
The Fallacy of the Stuck Plunger
--I honestly thought I had a stuck plunger because I followed the procedure in the manual to trouble-shoot rough running in one cylinder that seemed to be fuel-related. I determined INCORRECTLY that it wasn't due to the injector (it turned out it was), which led me to rule out the suction valve and the delivery valve and determine INCORRECTLY that it was the plunger.
--Reading further and talking with other folks, stuck plungers may be associated with tiis that have sat for years, but are highly unlikely to be associated with well-running cars. That is, the piston can stick from disuse, but it is unlikely to start sticking in a running car that's humming on down the road.
--I now know that, if a stuck plunger is suspected, the pump head does not have to come off. You can simply pull out the suction valves, which exposes the tops of the pistons, and use a thin non-marring wood dowel or plastic probe to push on the tops of the plungers, which, as per the photo above, are right there. You're not even sticking anything down a cylinder. This was described in another thread, but I didn't understand how it was possible until I saw that the plungers are not pistons. They're not fixed. They ride on springs. That's why you can just push them down.
--You also can pull the belt off the injection pump, rotate the pump pulley by hand, and verify that the tops of the plungers go up and down. They don't move by much -- maybe 1/16" to 1/8" -- but they do visibly move. If you see this, nothing is stuck.
So, that should largely prevent you from doing what I did. But...
If You're Thinking of Pulling the Head Off a KFish Pump, Remember:
--If you have to take the top of the pump off, when you unscrew the four Allen bolts holding it on, the springs on the plungers push the head up. When you lift the head up and out, the plungers will slide out of their cylinders. If you're lucky, they and the springs will drop down into the bottom of the pump. It's not that hard to fish them out. But if you're unlucky, they'll go over the side of the pump and fall down in the engine compartment. Not good.
--I don't know enough to know if the plungers and springs are matched for individual cylinders (or matched for delivery and suction valves), but when they fall out, you lose the correspondence of which plunger went into which cylinder, so it's really best not to let it happen in the first place.
--When you reassemble the pump and put the head back on, you can try putting a dab of Vaseline or some other gas-soluble grease in each of the cylinders to hold the pushrods in. Or you can curl four fingers around the right side of the pump head and put each finger at the bottom of a plunger, essentially holding the plungers in place while you manuever the head into position. I had to do it a few times so I got pretty good at it. It actually works pretty well.
--Knowing this, with practice, when you pull the head off, you could probably undo the bolts, let it rise up from the pressure from the springs, reach around the right side with your fingers, and get them in there and hold the plungers in place.
Like I said, I learned a lot...