Unclear on how to check for distributer pulse

[timmy2]

You are measuring the coil value in the distributor.

[thefaculty]

Originally Posted by JSV798

Your meter looks to be showing 575 K Ohms, so that's quite a high value (575,000 ohms). So cable would appear to be good. How exactly do you check for pulse between 7 and ground? What do you see on your meter?

Oh this is good news! Thank you - I assumed the .575 k - mean fivehundredseventyfive, another learning curve! Thank you.

So for the voltage test I setup previously as the pic shows below (DMM set to VDC, DMM negative to ground by coil, DMM positive to terminal 7 in pin, then crank) but right now I don't have a helper to crank the engine for me. I'll have to wait for the Mrs to get home and grab her as she walks in.

[JSV798]

Hang on! I didn't see the decimal point so think you are right with 575 Ohms. Perhaps Dennis can confirm that this is a good value for the coil at the distributor end where the cables connect. Still suggests cable is good. I'm looking at the wiring diagram on page 280-9 of Bentley.
What value did you get on the meter for the pulse?

Roy

[thefaculty]

Originally Posted by timmy2

You are measuring the coil value in the distributor.

Thanks Dennis - and does this look correct/good to you? We are getting 575 Ohms through 7 & 31D. We can't find a reference to what this should be.

[thefaculty]

I managed to grab the Mrs to help - this is what we got. Looks like a 1volt pulse which, if I have read threads and Bentley correctly, is good.... right?

[timmy2]

I can’t remember the value for the reluctor coil, but it is likely fine as they rarely fail.

[JSV798]

Definitely something happening but notice you have meter set to AC in video but to DC? in earlier snapshot. Do you get the same result if meter set to DC voltage?
Still odd that you don't get a pulse between 7 and 31d but did you have meter set on DC volts?

I know that you don't want to remove the distributor but to remove the wire at the distributor end it's pretty much essential as there's so little room. There is no need to lose the timing if you mark where it is clamped and set it to TDC on number 1 before removal it should be possible to replace it in the same spot. Once you can get at both ends of the cable you can check the cable out. On my faulty cable I was getting almost no resistance between any pair of contacts with the cable off the car.
Maybe you should wait for your new coil to arrive before going any further.

[thefaculty]

Originally Posted by JSV798

Definitely something happening but notice you have meter set to AC in video but to DC? in earlier snapshot. Do you get the same result if meter set to DC voltage?
Still odd that you don't get a pulse between 7 and 31d but did you have meter set on DC volts?

I know that you don't want to remove the distributor but to remove the wire at the distributor end it's pretty much essential as there's so little room. There is no need to lose the timing if you mark where it is clamped and set it to TDC on number 1 before removal it should be possible to replace it in the same spot. Once you can get at both ends of the cable you can check the cable out. On my faulty cable I was getting almost no resistance between any pair of contacts with the cable off the car.
Maybe you should wait for your new coil to arrive before going any further.

Yes earlier snapshot was incorrect (you have good eyes!!). I double checked Bentley and verified that reading should be done VAC. I actually did test it on DC first - just to be sure, and didn't get a reading that made any kind of sense. Bentley 280-9 instructs:

• With engine cranking test for voltage (VAC) between terminals 7 and 31d.
• If meter shows a voltage pulse, CDI control unit or coil are suspect.

...and I agree, I think so far it feels like I am ok on the Green Wire. Perhaps we are wrong but once the new coil gets here (which is taking it's sweet time) we'll know 100% and can go from there. Thanks for all your help so far Roy! You've been fantastic!

[thefaculty]

FULL END-TO-END GREEN WIRE SUPPLIER FOUND!!!

No update as yet on the non-start but this exploration has shown me that finding a solution for the Green Wire is hard to find as a simple plug'n'play option. The one provided by our host and most their suppliers is too short and need to be spliced in to the original cable and removing/bypassing the older, cooked section.

I hunted everywhere for a solution and ended up reaching out to the guys at Kroon Wire who make pretty much every kind of wire/engine harness you can imagine for all our cars. The can provide the CDI harness as a full replacement which includes the original Bosch Distributer Wire:

• https://www.kroonwireharnesses.com/index.php?route=product/product&product_id=711&search=6+pole

It is expensive but very well made and a great replaceent preserving the original wiring specs of our cars. However, after emailing them they are very aware of this issue and while it is not advertised on their site that explained the following"

• "We could also deliver a green wire at the right length with terminals that you can "click" in to the 6 pole connector. Please note that the distributor connector is not available as a single part (unfortunately) so will need to mount a 2 pole Bosch connector at the other end of the cable and that will connect to the famous short Bosch green distributor wire. (male to female). The price for this will be EUR85,- ex shipping ( the original Bosch wire is included)"

So thought I should share this here because it looks like a great option for anyone who needs to replace their Green Wire (perhaps me in a few days... we shall see)

[thefaculty]

I cannot tell you how happy I am to report back that the new coil arrived today, it went in and she started faster than ever before!!!

I cannot thank you guys all enough for your help, experience, wisdom and patience with me! For most of you this is simple stuff but for a newbie like me it's a milestone. Taking a car from a non-starter to a nice clean start without taking her to a shop is a big deal for me and I couldn't have done it without this forum!

THANK YOU EVERYONE!!!! And now enjoy the sweet sound of success!!

[JSV798]

Congratulations on fixing the fault. As a matter of interest I measured the resistance between 7 and 31d on my '78SC and it was 560 Ohms so pretty close to your value and confirmed that your green wire was OK. I bought my new green wire from my local Porsche dealer. Bit pricey but did the job. Originally bought the URO product but it failed after a month. Turned out it was a poor fit electrically and they did refund me.

[UROParts]

Originally Posted by JSV798

Turned out it was a poor fit electrically and they did refund me.

Unfortunately true for our first production run. Once we heard of the issue, we modified the inventory at the time to tighten the connection, though it's certainly possible there are still some wires with with the original loose connectors out there in the wild.

We updated the connectors for the next run, and they have a nice secure electrical connection and no complaints so far. If anyone has one of the early wires, please PM us with your purchase details and we'll be happy to send you the new wire at no charge. Or we can provide instructions on how to tighten the connector with a small nail or icepick, takes only seconds.