Help needed ”No spark mystery”

[BartdeBruijn]

Loosing my mind slowly……

History:
Good running 911T 1969 with CDI and Bosch distributor
After years perfect running intermittent ignition cut outs. Sometimes short, could restart sometimes towing back home.


CDI has high pitch noise etc. But as I wanted to rule out the old electronics I purchased a MSD 6A and blaster coil.

After installing MSD there was no spark at the test spark plug cilinder 1 connected to the distributor.

Findings & checks done
- When connecting spark plug directly to the coil lead and grounding the trigger wire (white) from the MSD if have many strong sparks.
- Checking my Bosch rotor with resistor turned out to have infinite/open resistance. Found stories about fried resistors.

Mounted original rebuild Marelli distributor with zero resistance between new rotor points.(coil wire input and cilinder position output)
- Same story, no spark from spark plug connected to distributor cil1.
- When checking the wire connected to the points from Marelli distributor with multi meter one reads the opening and closing of the points(zero and infinite resistance).
- When connecting the spark plug directly to the coil (to rule out rotor and cap of rebuild marelli) and connecting the white MSD trigger wire to the points wire(that measure open and closing) and rotating the crank 720 degrees to be sure that cil1 will go through compression TDC (to rule out some timing mismatch….no spark…..

So MSD fires when white wire is grounded and spark plug is directly connected to coil
Points open and close measured on wire that comes from points (the one that need to be connected to white MSD wire to trigger a spark
Though the points do give a ground (measured open and closing)the coil does not fire through the distributor cap - rotor - plug wire - spark plug route!

Help / advice would be highly apriciated!
Thanks,
Bart

[1969911T]

Seems like it is in the distributor. The capacitor if shorted would have the points always grounded and the CDI would not work. Also if the points are misadjusted so they do not open, the coil will not fire. Also there are insulators for the points that need to be inplace.
Good luck
Steve

One other possibility, I had a distributor cap where the center (spring loaded) pin from the coil was stuck and would not touch the center of the rotor-something else to check!

[BartdeBruijn]

Hi Steve,
Thanks!
That’s the thing, points open and close, checked with multimeter ( from 0 ohm to infinite).
When grounding the white wire from MSD and spark plug directly from coil I have a spark.
When connecting the wire to the points, who open and close, spark plug cil1 does not fire also not rotating crank 720 degrees to be sure…

Will keep on digging ��
(Can not be that difficult, probably missing the obvious….)

[1969911T]

Put a thin spot of grease on top of the rotor, put on the Distributor cap and clamp it down, then remove the distributor cap and see if any grease is on the center pin of the cap.

Try another wire going from the coil to the rotor. Maybe that wire is the problem
Steve

[BartdeBruijn]

Will try the grease tip (maybe there is no contact.....The other wire I already tried, also connect the coil wire to spark plug and grounded MSD trigger wire and had spark so coil lead is ok.
I made yesterday a test plan to trace down the culprit....If time I will try tonight and update ;-)

[BartdeBruijn]

Was a bit quick with text have to check something first
Will be continued!

[BartdeBruijn]

New status 01-10-2023

Build ignition to CDI again with refurbished Marelli.
When engine is at TDC compression stroke(checked on inlet valve cilinder 1 and compression gauge) I rotate distributor rotor using advance and by doing so opening points and creating spark. So far so good.

Now with the new MSD 6A including MSD blaster coil installed without rotating engine, so all is in the same position where I had a CDI spark, by again opening points by rotating rotor, I do NOT get a spark.
Indicator lamp of MSD is on.
Installation checked 100 times
- Big red wire direct plus
- Big black wire to good ground
- Thin red wire switched by ignition key
- Black and orange wire for coil (black to - and orange to +)
- White wire to points(distributor)
When disconnecting the white wire (trigger wire) from the points and holding mass I have a constant flow of sparks. So it seems to work opposite. The spark should jump when points open = no mass/ground. In my case I see a spark when I ground the white trigger wire(in MSD manual this one should be connected to the points.
Also checked again with multimeter that when rotating rotor points do open and close.

Any ideas?
Regards,
Bart

P.s. will call MSD representative in the Netherlands

[BartdeBruijn]

I decided to send everything back to Dutch MSD representative so he can see/test what I saw. Will update when more info is available