I have included a drawing of an injector I took apart. Could someone help me figure out how these things work. I see a oval hole in the body that is in line with a smaller hole that runs lengthwise thru the (1 ) body (5) spacer, then into the (7) nozzle. I assume that this is the fuel delivery port? Is it that pressure is built up in this port and that is what trips, or opens the spring loaded plunger in the nozzle. When I hear of someone referring to "pop" testing the nozzles is this related to the (3) spring and the (2) washer or spacer? I am guessing that there are different thicknesses of the spacer on top of the spring. What is the function of the straight hole in the spring chamber in the side of the body right above the oval port? Is it just so the chamber can vent, or does this aid in returning fuel that escapes the pressure side?

I must say that after taking this apart, I would not hesitate to put in a set of replacement nozzles.
Thanks in advance for any help with my questions.
Terry

 

The hole might be for fuel return into the cylinder head.

 

Anybody else have any thoughts on the operation of these things. This is not a statement of operation, as much as is it a series of little questions. If i I am right in my decscription of these things, please tell me so. I would just like to know what makes them "tick" so to speak.
Thanks

 

The injector is operated by the pressure of the fuel- due to the design the full pressure of the fuel is acting only on the lower side of the needle (plunger),

You can see the way this is done on this pic:


This injector type has the high pressure fuel entering from the top (not from the side into the bigger of the 2 holes like ours) Number 16 is the pressure channel where the high pressure fuel goes from the connector to the tip. The space above the plunger (number 7) is filled with the leak oil (non-pressurized diesel) that then goes into the return line. (The smaller of the 2 holes in your number 1 part- this one vents into the return barrel in the cylinder head )
The pop pressure is determined by the sectional area of the plunger and the spring preload. The preload is adjusted with the shim (Number 15). (You can't change the other variables)

Your description is incorrect in the point that you assume that the whole injector is under pressure- the trick is that there is a pressure difference between the tip of the plunger that rests in the nozzle and the other end of the plunger.

HTH

AlpineRAM

 

AlpineRAM thanks so much for your reply. I am guessing due to the pressure on the spring that the nozzle is only open for a very small time. Just enough to give a small shot. How does "tapping the wire on the VP" change this. The pressure must be intensified for a longer period to keep the spring open?

 

By the way, much better pic than mine.

 

I must admit that I "stole" the pic by linking to http://www.kfztech.de/kfztechnik/mot...sen/duesen.htm (A German site for vehicle techs)

The amount of time the plunger is lifted is very short. (only some degrees of crankshaft rotation)

The injector itself is only one part of the puzzle. In the IP there is a plunger that travels in a cylinder and displaces the fuel in there- the fuel will want to go somewhere (through the distributor, DV, inj. line to the injector) Since the injector is closed the pressure will rise (and the inj. lines will "balloon" ) until pop presure is reached. The injector is open and fuel flows as long as the plunger travels on- and the solenoit Teed in the line (within the pump) remains closed. Then the solenoid opens and the fuel can decide to go through the injector against the backpressure or just escaping through th solenoid- much easier. So the opening of the solenoid determines the end of the injection event. (The solenoid is closed with voltage to it) Since the computer on the VP44 will not keep the solenoid closed for the full stroke of the plunger there are wire tapping boxes that will supply electricity to the solenoid after the VP 44 comp would have shut off - longer injection meaning more fuel.

AlpineRAM

 

It is. The operation of the injector is as you described. High pressure fuel from the VP enters the large hole, goes down the injector and when enough pressure is built up to overcome the spring tension, it "pops" open and injects fuel.

When the VP's delivered pressure drops too low, the injector closes and the residual pressure is bled off into the return.

As far as I know, anyway.

h

 

That's not really correct. The residual pressure remains in the line (the closing pressure that is a bit lower than the pop pressure) - only the diesel that leaks past number7 in the pic is going to the return line. A new injector will have minimal leakage. On some injectors for the distributor style pumps there is a dedicated leak channel or a rather lose fitting between number 7 and number 6 that allows air to go through to the low pressure side rather quickly to faciliate the bleeding in case of air bubbles. (VW Rabbit diesel engines for example)
In injectors that do not have this bypass the injector will need longer to start injecting when it gets worn out, generating a later injection event with a lower pop pressure that in turn increases droplet size and therefore a much later effective timing of the burn. This leads to high EGTs (as known from old style extrude honed injectors without a timing box)

AlpineRAM

 

Thanks for those postings, Alpine!

 

Cool, now I'm getting a better understanding. Now I can see why there are recommended injector periods too. It would seem just like my ever so popular VP44, my injectors are only lubed with fuel also and there are more moving parts inside than I would have thought. The noise of the diesel engine is more understandable too, since there are a lot of hard metal objects all smacking against on another for every piston stroke.