checking grounds 82 928
 

Hi Everyone
Still working on the 82 928. Got fuel ,spark & good AFC relay starts & dies starts & dies will run for about 2 to3 seconds if I spray carb cleaner in the intake it will stay running checked all fuses in the fuse box. Green wire from distributor to ignition box, is good 14 pin connector has no frayed or damaged wires. load tested grounds@ the processor pins 5, 16,17&35 all prove out. I have B+ on both sides of the connectors that goes to injectors. Processor not grounding to fire the injectors. causing no injector pulse. do not believe it is a bad processor rather still a wiring problem. Like most Porsches & VW's I have worked on ground are a problematic issue As far as the grounds. I know about the ground under the air diverter valve on the right side valve cover will cause this problem. Is this ground tied directly to the processor or to somewhere else on the vehicle
is there any other grounds that I need to confirm that are good that would cause no injector pulse. also one other thing that I do not think is right either pins 10& 29 on the processor that power up the AFC relay load test good with key off but when you turn the key on to start pin 10 goes dim (which makes think it is a ground issue& pin 29 goes out that powers up th AFC relay Ignition switch issue?
Don’t want to throw parts at the car Just believe I am missing on link in the chain to make the car run What does to processor need to see to ground the circuit to fire the injectors?
would greatly appreciate any suggestions or info to resolve my issue with no injector pulse
thanks
KC Steve

Do you have a noid light to check that your injectors are firing? I would bet that they are not and you are running for those few seconds on the cold start injector until the fuel from that runs out. Check the grounds for your injector harness ( one is on the passenger cam cover).
Also, have you checked your fuel injection relay?(XVI, top row and 4th from the right) You can remove the relay and make a jumper that connects terminal 30 to the 2 terminal 87's (i.e. a three pronged jumper) that will allow you to determine if your fuel injection relay is working properly. If, with the jumper, you car starts and runs, just buy a new relay (928.615.119.00)and install it.

checking grounds 82 928
 

Hi John
thank you for your help& suggestions. My bad. forgot to mention I did check the injectors with noid light. & the three wire jumper for the relay. I have a 100% good relay. I did by chance I meet a Porsche mechanic yesterday he has been doing it for 40+ years. Very knowledgeable on 928s
He is saying like you the ground under the air diverter valve under the cam cover. go for it 1st also there is about 8 to10 grounds up by the right front headlamp which I found & inside near the processor. In the right kick panel. . The problem on 928's is the is so much aluminum the vehicle there is constant electrolysis going on causing ground issues. all over the car He recommended to me to ground to something steel on the engine when ever possible I am going for the grounds today . All along I felt it is just a ground problem. will keep you posted on how it goes
KC Steve

Mine would only run on spray when I first got it. I did all the grounds, relays and wiring checks. It turned out to be a big vacuum leak at the side of the throttle body where there is a plastic plug that over time gets very brittle. To check for a vacuum issue put a long piece of fuel hose down the flapper to keep it open. If it runs then start to look for big vacuum leaks.

Upon direction from stepson, I located the ground on the front top of the cam cover held in place w/ 10mm bolt. I was unable to turn the bolt head and it did break releasing the ground lug. The lug was heavily tarnished. Once polished and reattached the noid light did flash: dim. Upon a discussion w/ a BMW tech he confirmed a dim light is OK.

Just ground that wire somewhere else more accessible.

10/4 There is a ground at the #4 injector hold-down 10mm bolt. I was planning to use the 10mm at #1 injector for the cam cover ground replacement.