Let’s talk injectors

Ok, so since I’m married, with two kids, and getting older and fatter and balder all the time. The only thing I have to do on a Friday night is disassemble one of my old injectors. I wanted to see for myself what exactly goes on inside of one of these things so I dove in for a look.

With the thing apart, I spent some time blowing through all the holes, and shining a led flashlight through others to see how it works. The attached pic is my best understanding of how some fuel gets into the cylinder, and some gets returned. (After clicking the thumb-nail, be sure to click the pic enlarge button so you can see and read the whole thing.)

So I thought I would start this thread to see if I got the ‘how it works’ part right, and open the discussion on different code injectors, and which would flow more fuel.

Based on the picture below, wouldn’t it suggest that the later style injectors with higher pop-off pressures, would flow more fuel? It would seem to me that a heavier spring would cause more fuel to go into the motor, and less to be returned. :Sly

What do you guys think?

Incase there are folks that aren’t aware of this. When you open a picture on here, sometimes your web browser doesn’t blow the picture out to its full size. After you click on the thumbnail, if you hold your mouse over the picture the expand button will appear. Click on that and the image will be blown out to full size.

Looks like this:

Hm... interesting picture there. So when the fuel gets into the red area and builds pressure, how does the plunger work. How does it hold the fuel back until 1800 PSI?

When the spring gets squished enough does does that just mean the fuel that gets by goes to the return line?

The plunger seals at the top and the bottom, with a much bigger hole at the top. But the plunger can only move up. So, when you apply enough pressure, the plunger moves up a little, and allows fuel to spray out, and flow out the return path. So my thinking is, the spring acts as a pressure regulator. When the IP is sending fuel to the injector, the spring causes the pressure to be at around 1800, if it starts to go above this, the plunger opens more and more fuel is returned to maintian 1800 psi. this is all just my theory though.

Yep it's a regulator all right. Now in most cases you can shove more material through at a higher pressure but this is only true until you reach a point where no matter how hard you shove only so much will fit through a given size hole. I don't know the math behind it but I know the theroy. What would be best is to enlarge the hole in the seat some but then you would have enlarge the plunger to compensate for this.

I've never had one of these nozzles apart,when you disassembled that nozzle,did it have some shims in there?
if so those shims are how you adjust the opening pressure.
i've overhauled nozzles before,we have a nozzle tester in the shop and a pump shop just up the road from the store.they arent hard to do,just a PITA to get shimmed right.

yes, it was full of shims..

Rob, you should have been at the rally when I took 2 misfiring injectors apart and made one good one for EZ at the rally. You would have been proud of me as I did the rebuild on a tree stump but it worked.

Nice work Jim!

Ya, I should-a been there. Still kicking myself for missing that one...