No spark when cranking, but tries to fire briefly when I release the key?
 

1986 930-
Just performed under dash and fuse panel replacement and car won't start. I don't have spark when cranking. However, after cranking over for several rotations, when I release the key (from crank position to the run position) the car sputters and some exhaust smoke wafts out of the tailpipe. It's like i don't have spark when it's cranking but maybe I do in the run position.

Does that sound feasible? Could a bad ignition switch do this? Given the amount of wiring work I just did, I tend to suspect myself rather than suspect a part failure. The car had no such issues prior to the rewire.

Not a fun task. Sounds like switched connectors on the ignition switch. Common when fiddling in that area. Pelican has a section with wiring diagrams. Good luck to you Sir.

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This behavior is common after a rewire and incorrect attachment of wires at or to the ignition switch.

Several good threads to start:
http://forums.pelicanparts.com/porsche-911-technical-forum/373417-car-turns-over-but-doesnt-start-until-after-i-release-key.html and
http://forums.pelicanparts.com/porsche-911-technical-forum/910172-no-spark-when-cranking-but-tries-fire-briefly-when-i-release-key.html

Related:
http://forums.pelicanparts.com/porsche-911-technical-forum/434228-72-dies-when-key-released.html

Thanks for the replies. Some things to run down tonight

I thought the CDI ignitions didn't have the usual 12v to the coil and that you need an oscilloscope to measure 450v very briefly? I may be way off on this but this is my understanding fromsome recent reading. I'll try it for the heck of it tonight. Thanks

So some findings from tonight but still no spark-
CDI box whines with key on. Fuel pumps run
One in a while the car kicks over after cranking when I release the key.
I can't detect voltage at the coil when cranking or when on, but I think this is because the CDI sends pulses that a multimeter can't measure.

1. Coil has 672ohms between the center coil wire post and either of the little posts (in spec)
2. I get about .4ohms between the two little posts. (in spec)
3. Post 15 on 6 Pin CDI plug has 12.8v battery voltage with key on, drops to 11.2v while cranking the engine (is that too much of a drop?)
4. Post TD on 6 pin CDI plug right above post 15 has 7.8V with key on, drops to 7.1V when cranking (this one puzzles me... what is it, and should it be as low as 7-ish volts?)
5. Green wire ohms out at 675 at the CDI plug end

At this point maybe use an old spark plug connected to one of the spark plug wires and grounded to the engine. Then watch for a nice strong spark while cranking. If no spark you need to check for the trigger signal. The trigger wire is a COAX cable with inner conductor and outer shield. Not sure what you ohmed out. Did you measure from green wire to GND?

The TD connection is the output to the tachometer. It needs a pull-up resistor (inside the tachometer) to give meaningful signals. It will then show pulses (one per spark event)

The Bosch CDI should produce a spark down to about 7v although it will be weaker at a reduced voltage. 11.2 on cranking is fine.

The TD signal drives the tacho and should be around 7 volts so that is ok.

Are you sure the fuel pumps are running when the engine is cranking? Could you have misfired the fuel pump feed?

Maddening symptoms. I have the high tension lead from the coil with a grounded spark plug in the other end and am watching for spark as my son cranks the engine. No spark... until he stops and release the key, then I see one spark jump across the 10mm gap. Every time. Not a very bright spark, but one nonetheless.
If it didn't spark at all I would say CDI box or coil are bad, but the fact that it can spark drives me bananas. I don't know what to test next!

Thanks for ringing in here. No spark while cranking.
I measured the green wire by connecting my leads across the end two female spades in the plug. I guess that is to ground, if one of them is the ground wire. (Don't remember the numbers, but not the #15 one with 12v or the tach one, and not the ones that run to either side of the coil posts

could be as simple as a weak battery.

I hate to tell you that you need to go back and verify everyone of the connections you have touched. At this point, nobody knows where the error is, but it is something you did. FInd a wiring diagram make sure your wires are connected correctly. Pin numbers and wiring colors must match

Like I said earlier, with the rewire I do suspect myself and not some part failure. Yet the issue with that is that I seem to have exonerated myself by determining that the CDI gets power to post 15 when in run or during cranking. When that's true, this thing should try to spark.
Here's a video of the condition... you can see one spark when my son stops cranking and returns the key to the run position. (Note that this is a spare spark plug lead plugged directly into the coil with a spare spark plug in it. It is not one of the six posts off the distributor cap, thus ruling out cap, rotor issues)

Battery is fully charged as per my green light on battery tender. I have a 10A charger on it during the starting attempts for the heck of it. What a pisser if it does turn out to be the battery, but with 12.8V at run position dropping to 11.2V during cranking at the CDI harness post 15, I think that's ruled out. And the car cranks well enough as you can see below.
ON EDIT- battery from other car installed and same condition exists.

<iframe width="560" height="315" src="https://www.youtube.com/embed/WJ_-oPTkwLw" frameborder="0" allowfullscreen></iframe>

There is one condition where the CDI box "locks up" and the only time a spark is released is when power finally gets removed from the CDI box. Maybe it is time to find another SC and swap your box in or get a loaner CDI box and check if that fixes it.

Can you confirm the box keeps whining (getting power) while you crank?

What exactly did you rewire?

Ingo

Ingo, I cannot tell whether the box is whining during cranking. I do know I have power to pin 15 during cranking.

My rewire was clock, glove box and dash lighting circuit related. I did upgrade to one of Johny H's new blade fuse panels while-I-was-in-there. I wasn't near the engine compartment once during the job. And even after the meltdown, I started and drove the car home, where it has sat for 8 months while I found time here and there to perform the very tedious main harness R&R.

https://lh3.googleusercontent.com/qr...0=w962-h721-no

https://lh3.googleusercontent.com/yq...-=w962-h721-no

https://lh3.googleusercontent.com/L_...I=w962-h721-no

https://lh3.googleusercontent.com/jf...s=w962-h721-no

Then maybe the CDI box has a problem if you do have power during cranking in T15. What bothers me is the spark that comes way later. It's not because of s trigger signal but because the box is powered down. That typically tells you there is a fault in the box.

Ingo

As far as I can tell the op has not performed a voltage drop anywhere.

OP has an '86 930, but a Google search implies CDI box is for '69 to '77.
Which year cars have a CDI box ?

They all do, I was told. The CDI box in the 965 is called the EZ69.

GSX Ken, do you have a schematic of your car that shows the various control to the CDI box? There are two possibilities (at least)

1. Some control signal is keeping the CDI from discharging
2. The CDI is getting all proper signals, but it is defective

Having the bigger schematic does help troubleshooting. It is hard to do this over the web.