In my pursuit of thrift, I sought to use an old set of RX7 680cc injectors instead of buying new ones. Unfortunately one of the four ended up leaking up around the cap. I was told it could not be repaired. I wanted to find out why so I cut it apart and dug around in its guts. I thought I'd share the results with all of you.
First I had to remove the plastic cap to get into the real guts of the injector. That is reason one they can't be repaired by just anyone. I haven't tried just heating it up the cap and yanking it, since I had just one bad injector. But that doesn't matter much anyway once you get under that plastic cap.
The reason for that is the injector casing is compressed around the cap and has to be cut open to get to anything deeper inside. The metal is very hard and inflexible so I had to make mine into swiss cheese. Once you open it up you find surprisingly few pieces. The entire injector appears to be made of steel aside from the plastic cap, electromagnet, and the rubber o-rings. I believe the o-rings decide the fuel compatability of injectors with things like ethanol or alcohol. Those o-rings are also what appeared to be causing the leak inside of my injector. The cap seems to take care of some of the seal once those o-rings fail, otherwise the o-rings seal the fuel inside the electromagnet.
For those who are really curious how the injector works, it is amazingly simple. The large brown ring is an electromagnet that lifts the pintle up to release fuel past the tip. When the electromagnet isn't triggered the fuel pressure forces the pintle shut again. That's it, one moving part. Clean, simple engineering at its best.
The spacer indicated in the photos is the stop for the pintle and slips around the middle like a horseshoe. It also functions as a spacer for the injector tip. I used to think it set the opening distance but looking at it more closely the little lip poking out of the pintle does that when it hits the spacer.
I had thought adjusting the thinkness of the spacer would effect how much the injector opened, thus increasing the injector size, but to make that change you would need to add a washer in between the tip and the spacer or thin the stop on the pintle or machine the tip of the pintle. I have no idea how feasible doing any of that at home would be since the injector casing is also pressed around the tip. Not to mention you would have to be so precise it is just impractical.
On my 680 the movement of the pintle inside the assembled injector is almost unnoticeable. I'd estimate the movement to be less than 1mm. That tiny opening atomizes the fuel and makes the reaction time very fast.
Thanks for reading this. I always appreciate questions or corrections as well as thank you's if you'd care to write me.
Injector Disection: Why leaks can't be fixed.
