Porsche 928 84 no injection pulse Tech only please?

1984 928 sat for a while,spark ok,fuel pressure in specifications,no injection pulse,checked all grounds,replaced ecu and major realy,power to injection no flash at all,car will start with shot of H/c but stalls when
source quits..what am I missing ..
I have done my best to help volvo techs ? question
now I need a Porsche mind..
I am tech with 22 years but lost on this one..
it is my own car too,help save my face at the shop.
thanks no shots like did you attempt gas???

Check to see if you have a refference voltage at the injectors. Should be five volts min. If the voltage isn't there track back to where it picks up this voltage. The ECU supplies a ground on a pulse and width to the injectors, while refference voltage should be there constantly. Get some electronic cleaner from the parts store, and clean all connections that plug together, as well as the ECU. On the ECU disconnect the plugs, and look at them carefully for a bent pin, and clean the harness that hooks to it with the cleaner. Attach one lead of your meter to the signal pin for the injectors, and back probe the harness that plugs to the ECU. Use the High scale on your ohms meter. If you may be able to lay your hands on a book that shows the wiring chart for the system like a Haynes manual for this car or one like it, you may be able to tell which number of pin. If so you could just leave the meter in place while you shake rattle and roll the wires till you find the problem. I use needles, or paper clips to put into the pin holes. This way I can hook my meter to it with an allegator clip. you may want to have at the harness to the injectors a refference voltage wire, a ground wire, and a signal wire. though you do not get any flash on the noid light, you at least know the problem lies between the injectors and the ECU, "IF" the computer is good. You know there's generally a chance the computer is no good. If you back probe the wires and have good continuity up to the pins at the computer, it may be nothing else but a bad computer. Man.. I am happy it is you and not me, as some suff like this can make you pull your hair out. I hope I have at least pointed you in the right direction. Good Luck.

Certified Master Mechanic 35 40 years experience

Hello,

When you have grounds and supply for the injectors disconnect one of the injectors' connector and look if the injector is to get twelve V when the ignition is on, you may want to look if the LH Jetronic itself has a correct supply check relay of the L Jet .

Maybe this 928 '90 schematics may help you:

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Regards

i'll take a guess check to see if that car has reference and crank sensors. can not remember if they could control spark or injection signal. no reference signal to the ecu could because this.