AO

I was originally going to post this as a PM to Bill Ball because I know he's BTDT, but then thought everyone might benefit from this.

I'm working on a friends 928 that will not run. I've verified that the FP works, LH works in my car, EZK works, etc. I tried a little starting fluid and it ran for 10 seconds and quit. Oh... and relays have been swapped/jumped etc.

I put a noid light on it last night and cranked the engine. It would flash a few times but then go dead. Sometimes it flashed one time, other times it flashed a few dozen times. I tried this in a number of injector connections and the result was the same.

Now, in some of Bill's previous experiences, he's said he's found a one or more connections shorting to ground which as we now know takes all the injectors down.

My question is this, where was the short located and how did you determine which injector connection it was? Is there a way to narrow the list of suspects via a multimeter?

AO

Sorry Sterling, but what values should I be checking for? And would I be checking between the two point on the injector or between one of the points and ground?

Vilhuer

Check both connection from LH cable connector to injector connectors and wires from injector connectors to ground.

AO

Thanks Erkka. That makes sense. I'll give that a shot tonight.

Vilhuer

No make that check both connection from LH cable connector to injector connectors and that injector connectos receive 12V. Its LH box that gives them ground IIRR.

AO

Actually I thought you meant the LH.

So it looks like Pin 18 on the LH connector. Is this correct? And what I'm looking for is infinite resistance between this and the injector... right? Aww man, my head is starting to hurt again.

FlyingDog

The injectors are powered with 12V whenever the fuel pump relay is on. With the fuel pump relay jumpered, you should have 12V on one (and only one) pin of each injector.

Unplug the LH, engine harness at CE panel, and injectors. Check for infinite resistance between the two injector wires. Then check for infinite resistance between each injector wire and ground.

Look for the short under each of the injector boots and make sure all the clamps on the harness are not too tight. I'm not sure about 32V engines, but on the S2 engines the harness goes around the cam tower at cylinder #4 where there is a clamp. I tightened mine too much and caused the injectors to short.

AO

Nice description, Matt. THanks.

Z

Since this is a '91, it would have the ignition monitoring relay that shuts down half the injectors if uneven exhaust gas temperaures are found between the two cylinder banks. I'd take a close look at that ignition monitoring relay and the connections for it.

AO

Z-

True, but no lights. But it's proabbly best to take it out of the equation. I'll jumper it to see if that makes a difference. I recall somewhere, someone posted how to jumper it. now I just need to search...

FlyingDog

I think the coding plug wiring diagrams are in the WSMs. If not, I think they're posted here.

AO

MAtt-
We're talking about the Ignition Monitoring Relay whach measures exhaust gas temperatures and then shuts down the cold of the two to prevent a cat fire.

Z's theory is that this could potentially cause both banks to fail.

FlyingDog

I don't have one of those newfangled cars with extraneous sensors, but I thought part of the coding plug had something to do with ignoring the exhaust temp sensors on Euro models.

If not, have fun with the wiring diagrams!

Bill Ball

I think Erkka and FlyingDog are right. In our case we just peeled back the plug boots and observed frayed and shorted wires on 1 or 2 injectors. Or course, the short could be elsewhere, but this is by far the most likely spot. Peeling the boots is destructive, so you have have replacement leads ready.

Don't blame the ignition montoring relay, although you can take it completely out of the equation by jumping the relay's plug pins 1-3-5. [EDIT: WRONG! It's 2-4-5]

FlyingDog

I forget whether it was Tony or somebody else who had an injector that shorted internally. The injectors themselves should be 13.4-14.6ohm. Bosch spec for high impedance injection systems is somewhere around 12(IIRC) to 15.2.