928 at last

Any thoughts on how to fix? Been tapped..no luck.
Thanks!

928 at last

Should add that these are reconditioned and matched...so I'm not anticipating there's a mechanical issue with the injector, and the noid light shows good signal. Connection has been checked. What voltage do these normally run at? (Can it be jumpered to check operation)?

davek9

You can hook up a 9v Transistor radio battery (remember those) and it should click.
May want to run some brake clean through it, what make you think it is not working?

928 at last

Long story short, isolated why injector circuit #1 was going out. Stethescope indictates number 4 injector not firing which is causing the circuit to shut down under load.

davek9

Under load and or heat are hard faults to isolate for sure.
You could swap it to the other Injector circuit and see if the same problem follows your theory else just swap it out with another known good one.
What does that cylinders spark plug look like?

928 at last

Spark is nice and strong - fresh plugs and good wires. Seems like a couple of the others were a little sticky at first but fine now. This one just won't co-operate. I'll try and coax it with the 9V battery before I take out the rail again.

Hilton

I've used a 12v supply with a push button in the circuit to avoid cooking the inductive coil in the injector. Just tap the push button a few times to unstick.

928 at last

I've used brake cleaner and multiple 9V pulses and no luck so far.....
12V is next. I'm beginning to think the coil is defective.

Rich9928p

The fuel injectors are all wired in parallel. Battery voltage is provided when the ignition is turned on (1987 and newer) or when the fuel pump runs (1984 Euro though 1986 Euro/US). In all cases the LH provides the switch to ground (via a power transistor) with a good size capacitor there to handle the voltage spike.

Have you checked the resistance of the fuel injector? It should be in the 14 ohm range. As you might imagine, with only 14 ohms a good amount current flows with 12V across it - so don't leave it connected to a battery for any long amount of time or you can cook the coil windings. If it doesn't open, it is dead.

Tails

+1 to Hilton's and Rich's suggestions.

Measure resistance and if OK the try the 12 volt battery via a push button in the circuit.

Tails 1990 928S4 Auto

Imo000

Ahhhh you finally found the problem. Glad to hear it.
If a 9V won't open it, then 12 probably won't either but worth a try. As a last resort, swap it out with the old one untill you get a replacement.

928 at last

Yes, took some doing, and a drive up to Princess for the noid light kit, but finally was able to figure out that #4 wasn't firing.

Giving up now, it's been flushed with cleaner and pulsed with 12V with no response.

All old ones are clacking happily with the 9V, but for the sake of a couple days, I'm going to wait on the replacement and then button it up. Should be operational by the weekend. (Which would give me an excuse to criuse over to your place and be a nuisance)!

Soon,

BIMMERMIKE

operational by the weekend. (Which would give me an excuse to criuse over to your place and be a nuisance)!

Make it a Friday afternoon and I can join you and Imre....

928 at last

But this coming Friday is a definite possibility if all goes as planned.....
I'll keep you posted......pun intended.

Imo000

Mine is still in storage but you guys can come over and have a look at Marc's '89 S4. I'll be working away on it, putting the TT back in.