Bill Ball

Here's the relevant area of the 88MY (same as 87) wiring diagram. It's a little confusing initially because it shows what appear to be split power sources. However, wire junction points 1 and 4 are both fed 12V from the same LH relay output. I've shown those wires in red, but the relay is off-screen. Wire junction points 2 and 3 are fed 12V from pin 18 on the LH brain, with that feed path shown in blue. The LH takes this side to ground when it batch fires the injectors.

G Man

So what was the official diagnosis. I did not see the cause of the issue listed. Glad it is fixed.

FlyingDog

Post #29 on Tony's thread is pure genius. Bill Ball had another good thread working on somebody else's car.

G Man, post #22, injector connector for cylinder 5 was shorted.

Bill Ball

Actually, I don't think H'man has his diagnosed yet. His post saying "Done" I believe refers to him changing the thread title.

Dave H.

see post 22. that's H's car John Davis and I were working on last night...

dr bob

H--

What's the diagnosis?

Bill Ball

OK, I misunderstood. Post #22 is by Dave and I thought refered to a similar problem with his own car. If this was H'man's car, then they found the frayed, shorting wires and fixed them.

dr bob

OK, guilty of reqading the cache'd thread without the results. Glad it works!


Before we vote on the diagnostic post for any 'of the X' honors, be aware that I've never had the rail covers off on my car, have a good idea where the ignition monitoring relay lives, and would have to crack the manuals and a lot of posts to find out which pin is 18 once I figgered out which controller is the LH.

But I do have the WSM's with the wiring diagrams, plus I spent a week in a Holiday Inn Express earlier this month. The smarts are wearing off fast though.


Off to finalize a parade plan, hopefully followed by some dinner.

the flyin' scotsman

Thanks Bill............much appreciated.

One of these days I'll figure out how to colour a wiring diagram like that.........need special software?

Ninespub

Dr Bob: If the info you provided helps Andrew and the Detroit 928OC gang get my '91 running, Dinner for you and Andrew and the rest of the group is on me in Saginaw, Michigan's finest Steak House; which I and my bank happen to own (.....uh, actually I think the bank has the bigger half) HOWEVER, you spring for the airfare. Thanks in again for your efforts!

Paul Barrera - '91 $4 ........DOA in Andrew's driveway!

dr bob

Paul--

Let me know how it goes with your S4. The basic diagnostic is the same for your car as it is for H's (and all '89+ 928's). At least we now have some good numbers to look for on the two circuits, and should be able to at least halve the number of connectors we need to pull in the engine bay.

Need to spend some time with the injection harness on my car one of these days. After the parade though. Started at 6am today posting no-parking signs, just dropped of a busload of VIP guests after 10PM. A couple more days of this to go plus an all-nighter the 31st and into New Years Day. Have great game tickets but will probably sleep instead. I'll DVR the game for later I guess. I'm getting too old for this stuff...

heinrich

Bob I just want to thank you sincerely yet again. I was on speakerphone for a very long time with John and Dave yesterday as they worked on the car, and I read them all the posts in this thread. Later it was decided that they should go print it out for themselves. They followed your recommendations which led them to the exact injector with the fault. This was MOST helpful and saved an amazing amount of effort for us all. Thank you, I would like to buy you a very large beer Also, thanks to all my other friends who helped in this thread, and personally, including DaveH.
Heinrich

Dave H.

it was just as much John. someone had to plug in the injectors while i watched the meter...

Peter F

This is a great method for the newer cars posted by Dr Bob.
Seems to become a more and more common problem as our cars get older with shorts in the harnesses.
I tested all my injector connectors recently in the chase for an intermittent fault on my car and in the end found the problem in the MAF harness near the connector with frayed and sometime shorting cables.



/Peter

dr bob

The problem that Peter had with the MAF wiring can be diagnosed in a similar fashion from the LH plug. With the WSM diagnostics and John Speake's various instructions for testing, one should be able to use a meter to 'see' shorted MAF connector wiring without popping the bonnet.


I confess again, in front of my brothers and sisters here, that I am way lazy and always looking for the fastest/easiest/least invasive way to diagnose. We got lucky on H's car, mostly because the others had already decided what the prolem was. We were just confirming the previous diagnosis before ripping in to the belly of the beast.