MrShaw

It saddens me to post here again, after scouring the forums for a solution I am once again, stuck.
We finally had the 928 running, after months of painful diagnosing and many replacement parts. Long story short, we found the vehicle would run under it's own fuel pressure with the MAF sensor disconnected.
Using our oscilloscope, we used the voltage generator function to compensate for the voltage the MAF wasn't adding, finally, she ran buttery smooth, purposefully not for long as the cooling system wasn't assembled fully.
Leaving work on a high, I came back the next day and continued to tidy up the car, I should have checked it still started before touching anything. I put the alternator belt on, cooling fans and hoses on. I re-routed the starter motor wires so they were tidy. I knew the car would run with the MAF unplugged so decided to try again.
Dead, she wouldn't start. It wouldn't even run on starting fluid like it used to before the seized fuel pump was replaced. I checked for spark, no spark all of a sudden. We couldn't hijack the MAF again as it didn't seem to be getting power. I have checked all the grounds, again, for the third time, by continuity testing them. There is 0.5V at all the usual relay terminals 87 for the fuel pump etc, not 12v like there should be, even with key in ignition posistion. Little bit of history, this car essentially always cranked and had spark (after replacing CPS and fixing wiring) but never started without starting fluid, we found the kickdown relay was preventing injector pulse so took that out. We had injector pulse but it still didnt run, unplugged the MAF and she started but wouldn't rev, that's when we hijacked it with the scope and got it running perfect.
I am honestly stuck, I do not understand why there is now no power where there should be. Any help would be greatly appreciated. There is a much bigger history to this car so I am more than happy to clarify and answer questions, thank you guys so much, you've all been legends. The plan was to sell the car, as I am out of money and my life circumstances have changed, I just wanted to prove to the prospective buyer the car did run, even if the MAF needs re calibrating.

Mrmerlin

put your computer LH into a known good car and see if they work

MrShaw

I live in New Zealand so 928's aren't very common here. Is there any possibility that me touching the starter wires and moving the alternator around has done something? It seems like a funny coincidence. I have 12v at the jump posts, but not at the relay terminals for the fuel pump, EZK, LH etc.

FredR

You should see 12 volts at terminal 30 on all three relays at all times- the feed comes directly from the battery.

One of our Rennlist friends in NZ lives about 200km or so from Canterbury as I recall and he is very knowledgeable regarding the S4.

MrShaw

Ok, I definitely don't have that, I'm going to try a new battery and will just recheck the 12v wires (alternator and starter) that I touched last weekend.

Kevin in Atlanta

If you have 12 volts at the jump post the starter and alternator wiring is fine and you don't need a new battery.

But, you really need to check the red wires at the battery. Are they tight? They are a direct feed to the CE panel and computers, etc.

See if you have 12 volts at the red wires on top of the CE panel. If not then you found your problem.

MrShaw

One thing I forgot to mention is, when cranking, the Tach needle doesnt bounce, it shoots to 4000rpm and stays there for the duration of cranking, does that give you any clues?