Interesting link:

Info on Injectors

Got a couple of private responses to this issue I'd like to share, and add further info to. Thanks to Greg Nichols and Rory Hart for their responses and hope you guys don't mind me sharing your thoughts with the list.
From Greg:
I had my injectors rebuilt by Marren Motorsport back in June.  In talking with the owner, he mentioned that my year 928 used special O rings that he can not get from Bosch.  He must buy them from Porsche.  He told me something like, "If your car uses the thicker, orange O-rings, those are the special ones from Porsche."

Our cars are different model years, and I know for sure that they use different injectors, but hopefully this will be of some help to you.
'87 S4
From Rory:

Similar probs here.  I'm sending my injectors in this weeks for calibration etc.  A fellow lister help with the R/R and noted that while he intended to do what you are up to, he ended up throwing in the towel and sending them in to be done, because he was having a fitting prob.  When the injector shop got the them, they immediately called him to ask where the %&#@ did he get the fitting for the injectors.

So, what did my fellow lister tell me to beware of:  apparently there are a lot of places (including 928 shops) that will give you generic Bosch parts for your injector.  Hence, if the o-ring is loose, it isn't right.  I've been told it should actually be a very snug fit. Just my $.02.
Roy Hart
My additional thoughts/questions/info

Ironically, the original support rings are orange, but the new rings (gray) are, in fact, thicker at 3.415mm as opposed to 1.98mm for the original orange ones. Other than that, the rebuild seems to be fairly straight forward; Replace the rubber o-rings (3 ea), the plastic/composite support ring, and the plastic protective sleeve (tip). In examining the injectors, it is evident that (unless damaged) the support rings can be reused and that the components critical to rebuild are the rubber o-rings and the plastic protective sleeve/tip. With that in mind, if I cannot source the proper size
support rings, I'll simply reuse the originals as they are in excellent shape. As some additional info for anyone that might be able to point me to the source for the proper sized support rings. My injectors part No. 280150706 Bosch kit No. 1 287 101 704 Part No. of incorrect support ring in question 1 280 320 052 Again, I thank Greg and Rory for their replies, and anyone else that may shed some light on this problem.

1985 S Auto
Proud Member Of:
Rennlist & 928 OC
928 GB List ?!?!
Ross Racing In 2000 Keep The Faith

Injector cleaners?

Techron by Chevron I believe is the way to go. I think it's even Porsche recommended.

 Sta-bil fuel stabilizer instead. An off-road racing enthusiast turned me on to this stuff as a way to get the gunk out of my racing moto carbs.
He suggested I use it rather than any of the other stuff that doesn't seem to make much difference and he was very right on. Used it in my Honda Hawk with great results. My Jetta-motored VW was having some throttle hesitation issues. Traced it to the fuel system, so before I took it to the shop for a full on F.I. checkup, I added a 10oz bottle of Sta-bil and drove it through a tank of gas.. Problem gone!
I must have bought 25 bottles of Techtron (or it's equivalent) and never felt much improvement after using it. This fuel stabilizer, however, had worked for me twice in two tries...Your local TrueValue hardware store, in the chainsaw department. Or perhaps the garden shop and the Lawn mower section..
Don Hanson

Checking Fuel Injectors

If engine can be operated, pull off plugs on injectors separately. If fuel injectors are okay, engine speed should drop each time.
If engine cannot be operated, measure voltage on one plug of injectors against ground.
One of both terminals should have battery voltage.
Measure coil resistance of fuel injectors.
Specification: 15 - 17.5 ohms  (+15C...30C / +59F...86F).
While starting it is easy to hear the injectors activate (clicks). It helps using a long screwdriver as sort of a stethoscope.
Monitor the injection pulses with a oscilloscope.

Some think injectors fire individually on a 928. That is not true. All 8 injectors fire simultaneously, spraying fuel mist into the intake cavity that gets sucked in via the inlet valves of the cylinders.

Theo Jenniskens

1992 928GTS midnight blue