put the old coil back in.
NOTE did you buy a Porsche green wire, IE the more expensive one ,
Remove the non fitting part.

After more investigation I also suggest that you get this relay.

XVII Fuel Pump relay 928 615 113 01
After you fit a proper green wire replace the Fp relay and try to start the engine,

 

Stan , fuel injection relay ? it's a CIS car ...

 

Thanks sorry using a a diagram for US car

 

My gut says the voltage reading at coil 15 terminal is way low. I expect to see 9 or so in other cars. I don't have an early 928 to check. Anybody?

 

indeed dr bob.... that was my first thought too checking my ignition... till i read the WSM. Strange to see there max 5V !!! ....due the ignition module.

 

Yes Wsm quotes min 3v

 

Well I've done some more testing . The voltages seem within spec. Following the wsm it suggests the sensor is faulty inside the distributor. Not sure how or why they fail . I'm going to have to swap it out with a known good distributor I guess . Still a stab in the dark as I've not heard of this failing before ?

quick question : what should I expect the resistance to be from the central carbon brush inside the dist cap and the outer connector that the coil lead plugs into on the outside of the top of the cap ?

 

Before you replace any parts or take the distribution apart replace the green wire with a Bosch green wire

 

Waiting for my replacement green wire . Put the old one which looks fine back in temporary.

i have discovered that I'm not getting any extra voltage at the starter motor connection at the ballast resistors when I crank .

Checking on on the starter motor post I'm not getting any output when I crank the engine over .

Could this be significant ?

 

It definitely is significant.

There's a thread in the last year or two, related to a member fitting one of the IHI aftermarket starters and having slow or no start. In that case, a small relay was fitted to duplicate the function of the aux 51 contact in the starter solenoid during cranking. Look at this thread https://rennlist.com/forums/928-foru...i-starter.html which describes the issue and solution.


For those playing along at home, the starter solenoid plunger connects to the linkage to extend the Bendix over-running clutch drive at one end, while the other has a copper disk that connects the business end of the posts that connect to the start motor and the battery cable. There's an additional contact for that aux terminal, so it receives battery voltage at the same time that the starter motor is connected. The copper disk is not rigidly connected to the solenoid plunger, and has a spring pushing back to release everything when the solenoid coil is de-energized. The spring tends to slightly rotate the copper disk with each use of the starter, distributing the contact points around the face of that copper disk over its life. A well-used disk will have a ring of arc damage on the contact face. hat damage will prevent current from flowing through the aux circuit. During "rebuilding" or "reconditioning", the money-saving method is to flip the copper disk over. Since the contacts in the end of the casing from the motor, battery terminal and aux 51 are hard to get to and service after they were molded into the end of the solenoid case, they seldom see any clean-up. Further, it's too easy to set that copper disk back more rigidly on the end of the plunger so it doesn't flex to hit all three contact points. Early cars with the ballast resistors need that extra ignition voltage while cranking, and will be harder to start even with a new battery, and may not start at all if the battery is aged or otherwise discharged. Later cars 928, especially with EZx ignitions, no longer rely on that contact or ballast resistors to help compensate for voltage drop during starter cranking.

 

did you check Page 192 point 8 ?

 

Would adding 12v to that starter connection at ballast resistor and at the time of cranking eliminate this from the mix ?

 

Thanks belgianbarry Page 192 point eight result shows open circuit . I think these connections lead through the connector on the fender into the green wire and connected to distributor coil pick up .

Following on , testing the green wires old and new show near zero resistance end to end confirming that the wire is physically ok as far as can be told with a resistance test . It's a bit fiddly trying to test the connectors inside the distributor in situ so I reconnected the known good green wire and tested the resistance at the other end of the green cable and that showed open circuit .

IF I'm right in my thinking that the coil pick up should have a resistance reading of 485 -700 ohms which of I course I have open circuit .

Surely this must mean my distrubitor is kaputt ??? Or have I totally misunderstood the testing procedure ?

 

Yes -- that's exactly what the proscribed added relay does in the thread I linked. The key is that you need to get the 12V from the battery cable connection at the starter, before the losses on the way to the ignition switch. Adding the SPST mini relay by the starter solenoid is what makes this modification work. Clean the connections at the 14-pin under the hood too, as the 51 wire from the solenoid to the resistors is part of that front-of-engine harness that passes through that connector. The rest of the wiring is pretty crispy and deteriorated in original harnesses, so part of your recovery effort might include replacing that harness with a new one. There are several who make replacement harnesses, using modern fine-strand tinned marine-grade cable, correct color codes, and modern insulation and heat sheathing. They aren't cheap, but having new wire and connections in that harness seems to solve a slew of sniggly electrical ghosts all at once.

 

Correct... your sensor coil in the distributor must be broken.