Help needed “no spark” mystery
 

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

Did you check the factory wire harness (trigger wire) between the CDi end and the Distributor end?

Hi,
I believe you mean the wire going from the CDI (in my case a new MSD) to the wire comming from the distributor points?
This wire is new as coming from the new MSD.

I’m thinking return it to stock rather than adding another element to complexity. Wring out each wire an when checking each wire, move it around a bit to see if the wire opens. Check the connection pins/spade terminals and make sure they are clean and have enough tension to maintain a sound junction.

I am about to build back to stock (original CDI) or even no CDI….

On the new MSD unit I am trying to understand the following:
- System switches on by ignition key as should
- Light on MSD comes on as should
- MSD test procedure says to touch white wire to ground and remove from ground to initiate spark.
- Remove white wire from ground should create spark. In my case grounding white wire create sparks….
This white wire connects normally when not testing to points that will work as ground / no ground switch
Seems to work different / opposite from what manual says.
There is no option to connects wires wrong as there is a multi-connector going to the MSD unit

I am lost!

Regrds,
Bart

Does it spark while opening and closing the points with the white wire on the points and the spark-plug connected to the coil? I think you said the points do ground when closed. I think it fires when the white wire is opened on your factory test procedure. That is like conventional old school systems.

I had problems with points wearing out on my ‘72 911T and went to a PERTRONIX point conversion.

I was a bit quick with my latest text…
I build back my CDI setup and when connected as you mentioned it does spark via coil direct to spark plug. It is at TDC compression stroke (checked via inlet valve and compression gauge and when rotating the rotor via advance points open and close and while opening a spark can be seen.
Remembered I did the same with MSD but start doubting now.
However I will build exactly in this position the MSD 6A 0lus blaster coil back in and rotate rotor….. should give a spark, right!?
Will be continued…..

Make sure your battery is fully charged and connections ground et are all perfect. Then call MSD they’ll help you out.

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

Very strange. What i’m getting sitting in my armchair is that there is something wrong with the MSD. Having the trigger with points closed is opposite of what you want. So sparking all the time except when the spark needs to happen is wrong.

Did you contradict yourself?

White wire grounded = constant spark.
White wire opened starts sparking = triggered constant spark upon opening.

I’m not sure what you mean using the word “mass”.

Your wiring sounds correct. Maybe call the manufacturer?

Correct me if I’m not getting it.

I'm not entirely sure of the way the points+CDI works in these cars, so let me throw up a caution and ask one of the experts who really knows to jump in.

In a standard points ignition, the spark occurs when the points open, and interrupt the primary current to the coil. However, on many CDI systems, the points closing actually signals the CDI box to trigger the spark, because the primary coil current does not run through the points. As I said, I'm not sure about 911's, so consider that possibiity in your troubleshooting.

Thanks for responding!

@porschedud996: mass means grounding the wire(bad translation from Dutch to English …)
I contacted the sales representative for Europe and will maake some movies to show that things work opposite. Will put movie here also.
I am working on this for a week now and slowly start to believe something is wrong withe the box

Will post movie so people can see what goes on. Maybe the MSD box.

@PeteKz
The way you describe when a spark occur is also my understanding and also how I can get a spark using my old Bosch CDI box. The MSD should be a new version of the CDI with modern electronic.
If it works the other way arround it will not work. Furthermore the troubleshoot page of the MSD also says that it should fire the traditional way as you explained.

Will be continued….

Regards,
Bart

Bart thanks for confirming the CDI and MSD operation.

You may have already done this, but let me suggest again that you make sure all the connections through the harness to the CDI and the distributor are clean and tight. Power to the CDI could be getting interrupted by a poor connection. BTDT.

Bart, are you in the Netherlands?

The only way it must work correct is if spark occurs when the white wire is "lifted" from ground. If you are getting a spark when you initially touch it to ground, the MSD box is not working right. It should trigger exactly the same as the old, original Bosch box. Now, it can be a little tricky when you 'touch' the wire to ground because your hand may shake a little or the ground surface is not clean and the connection may make intermittent contact, as if there is 'switch bounce', making multiple contacts that the MSD sees as a "lift" from ground, so make sure you are not fooling yourself.

Which coil(s) are you using?

It's been awhile since I've had to mess with converting to MSD, but I thought that the MSD needed a regular type coil (NOT CDI). But if you hook up an MSD coil to the factory CDI, it will work without any problem. Just not the other way around.

Hi!

@PeteKz
All contacts/connections are clean and wires are ok.
CDI box works fine, the MSD seems to fool me.

@Porschedud996
Yes, I live in the Lowlands!

@Bob
Fair point and I relized that making ground could fool the system by reconnect / disconnect by shaking and or non clean ground. Therefore I used the points as a ground/no ground switch. So when I am at TDC compression I can twist the rotor a bit using the advance weights. By doing so I can open/close points. Checked this with multimeter to be sure. Using this approach the Bosch CDI gives a spark but the MSD does NOT. It is not that the MSD does not work as when I remove the white wire from the points and ground them I do get many sparks and the MSD light turns green. Again underlining your point that it could be my shaking hand. However the points that open and close should give somehow also a spark, right!?

@DannoBee
For the Bosch CDI I use the original coil (black with Orange/brownish top.(CDI works as explained)
For the MSD I used a MSD blaster coil that was the package deal.

Will try to shoot a video tonight to show.

Bart, I lived in Amstelveen back in the 90's. Yes, you are right, of course using the points as the trigger and gently rotating the distributor weights should cause the box to fire when the points ever so slightly lose contact. You have a mystery that seems to point directly at the MSD. I am not completely familiar with the MSD, but is it possible it is operating in a mode where it is set up for a reluctor distributor pickup (like used on the Porsche SC)? In such a setup the trigger signal is an ac waveform and I believe MSD triggers on the rising edge (going positive). Maybe this is just a configuration issue, and it needs to be set up to trigger from points ???

Hi Bob,
So we can speak Dutch….
I live in Enschede, eastern part and more green.
Yeah it is a strange story, must be something you said.
Drives me nuts. I like the original stuff, but once in a while my ignition suddenly died. Tried to find the culprit but was impossible to trace as happened rarely but was very, very anoying. Your car dies in the middel of traffic or at night somewhere you don’t wanna park it…

Therefore thought to replace the old electronics and see here I am pulling my hairs out ;-)
Will make the movie anyway as damn the MSD can spark, only at the wrong moment.

Will send everything back to be tested at the MSD representative.

Klein wereld! Ik heb in Amstelveen gewooned, werked bij ERICSSON, hoofdt kantor in het WTC Amsterdam voor drie jaren. Maar, ons engineering lab werd in Enschede, dus Ik rijdt over Holland een keer per week voor vergaderingen, etc. OK, mijn Nederlandse is officially "helemaal slecht"! ha ha Great country, still have friends there and one very good friend who I hired to come here in the states and is now living here full time. I hope you can sort out the problem. Check my website www.ashlocktech.com