1983 928s
Car starts and runs with cold start valve energized (12V supplied by jumper).
Stalls as soon as cold start valve turned off.
No electrical pulses to injectors.
Suspected AFC relay. Relay jumped still no change (yes, 3 wire jumper)
Getting 12V with key on to 30 and jumped 87 and 87a at relay but no voltage to pin 10 and 29 at 35 pin connector.
Questions are, does any fuse protect AFC computer (seems as though car should run with all fuses except fuel pump fuse disconnected?
How to trace path from 87 and 87a to pins 10 and 29. Something to do with the lower 25 A to X connectors? Have shop manual but wiring diagram
difficult to trace.
Appreciate any suggestions.

 

I would suggest that you have a good Bosch green wire.
NOTE some of the URO brand wires were defective.
Then make sure you have a fresh fuel pump relay ,
and fuel injector relay installed.
dont try jumping the relay positions on this year.

 

Thanks Mrmerlin,
But car runs with only cold start valve energized and getting good spark.
Both connectors of green wire fine.
Getting good fuel pressure and flow so not fuel relay.
Question is why no voltage at pins 29 and 10 with AFC relay jumped (and with good spare AFC relay).

 

did you clean the grounds on the right cam tower. then above the CE panel,
then do a CE panel refresh.?

 

There are two discrete ground points on that passenger side cam cover. The one buried beneath the air pump emissions valve requires that item to be removed in order to properly clean.

Go to google search, type "rennlist 928 forum Ljet pinout". That will yield a 2004 post by rich928 in which he provides a pinout for 35 pin connector. Both rich928 and porken have posted about ljet wiring over the years. There are a few good posts on the subject.

Forgive my inability to post the links from my archaic phone. I can do screenshots though.



The Ljet computer has, in my experience, become the primary root cause of stumble non start in mid year cars in these later years. Now when troubleshooting I'm suspecting that early, and swapping boxes to reduce suffering.. BTDT, was mislead by the previous wisdom that the ljet computer is unlikely to fail.

That said, you got to do certain basic checks first. Checking greenwire integrity, cleaning fuse contacts, etc. Frayed wires at afm and injector connectors...

Yes, power to computer is unfused. But the process of removing CE forces the reseating of the various wiring terminals distributing engine control signals, in lower right set of plugs esp. Plus enables cleanup of other basic problems throughout. Most cars i work on sat a long time and need it. So, do the cleaning of CE and ensure good grounds at that cover. Verify green wire, pull covers to check timing gears vs crank pointer vs rotor alignment on mark on distributor. Chances are the culprit is ljet box at passenger footwell.


From rich928s 2004 post

 

Thanks for the replies.

Remember, engine starts and continues to run with just cold start valve energized.

I have already found the problem. It is a poor connection between AFC relay and 35 pin connector.
No power to computer, thus no signal to injectors.
I was really looking for the path from 87 and 87A from AFC relay to 10 and 29 of 35 pin connectors.
Does 87 and 87A go to one of the A to X connectors at the bottom of the CE panel? I yes then I could isolate the problem.
I'll try studying the wiring diagrams again.

Without that information, looks like I will have to remove CE panel and clean all contacts.
I already have print out of 35 pin connector and all test good except #29 and #10 (including ground connections, which I cleaned again anyway).

Thanks again for your help.