Weak spark troubleshooting

[daniel911T]

Hey everyone!

I have an MSD 6AL and a Blaster SS coil in a 1969 Porsche 911. I am using a pertronix in the stock Bosch distributor for triggering. Coil wire is about 2' long 8mm MSD. Plug wires are 8.5mm Magnacor competiton wires (from our host). 6AL and Blaster SS coil are about 7 years old, but have driven less than 10K miles.

I have just installed a new set of Zenith carburettors and the car has been sitting for about 5 months. It was running when stored.

I have a no/weak spark problem now:
1. When the coil wire is placed close to ground (1/4" or closer) and the white wire is grounded I do get a spark. No spark at the 1/2" directed in 6AL instructions.

2. When I place the coil wire near ground and crank the engine, I do get multiple sparks. (Pertronix works)

3. When I attach a spark plug to the end of the coil wire at the installed gap (.060" Bosch WR5DC+) and ground the threaded part of the plug, then ground the white wire, there is no spark, but I can hear the MSD making the normal noises (high pitched noise)

4. When I attach a plug with a much smaller gap (.025 NGK BP6ES) and do the same proceedure, I also get no spark.

Battery is fully charged and reads 13V, engine cranks quickly.

What could cause this weak spark condition?

Thanks!
-Dan

[daniel911T]

Please guys!

Is there a way I can isolate this to either the MSD or the coil without buying anything?

-Dan

[snbush67]

Recheck the ground wire and connection, that is all I can think of. If the connections are all tight. Are you sure you have the terminals of the coil connected right? I think black and orange are sized so the ends only fit on the right terminal.

Have you tried to start the engine? Are you sure you aren't getting a good spark, if you are in normal lighting you might not be seeing the spark.

[steve911T]

Dan, During the time you were working on the Zeniths, did you remove any part of the ignition, distributor, pertronix, wires, plugs, etc? If you did, maybe something is in wrong, like the distributor is 180 degrees off. I did what you did, rebuilt the carbs, replaced the Marelli with a Bosch, etc. and them took me a year to get it right. Now I stick to one project at a time, carbs only, ignition only and rebaseline the car after each project. According to your last post (how much you disliked Zeniths), you did say that you were getting a spark. That has changed?? Steve

[Bobboloo]

Probably a bad coil.

That's usually what causes a weak spark. Sometimes coils get damaged when they are installed if they aren't hooked up correctly and can't discharge properly.

See if you can get the specs on the coil and test it with an ohm meter.

[Bobboloo]

Found the specs on MSD forum.

secondary resistance...4.5k
primary ---------.7 ohms

[daniel911T]

Shane,
I have checked the grounds and all read 0 ohm. All seems to be functioning.

Steve,
I didn't do anything except remove and reinstall the carbs. It wasn't until I was pretty sure that the carbs (with some parts from yours. Thanks again!) were doing about what they should and I still wasn't even getting a tiny pop, that I started digging into the ignition.

The coil wire throws a weak spark, but won't make a plug spark.
All my cranking was on a motor with no sparks.

Bobby,
I'll look into the resistance when I get home. We shall see...

Everyone,
Part of the reason I asked is that I don't know what the life expectency of a coil is? Is 7 years of light use a normal(ish) life for an MSD, or any, coil. I seem to remember them lasting longer.

Thanks for all the help!

-Dan

[HawgRyder]

Coils last either forever or....until they go bad....LOL
Sorry...poor joke.
But....if the coil goes..it goes...and a replacement is not going to break the bank.
I use the MSD coil...got it from the local auto parts place...works great....#8222 if I remember correctly.
Bob

[daniel911T]

Originally Posted by HawgRyder

Coils last either forever or....until they go bad....LOL
Sorry...poor joke.
But....if the coil goes..it goes...and a replacement is not going to break the bank.
I use the MSD coil...got it from the local auto parts place...works great....#8222 if I remember correctly.
Bob

Bob,
Thanks for the input. I'm looking for the 8222 high vib coil, I'm just having trouble sourcing it locally. I will mail order if necesary, but I'd rather not. There has to be a shop around here that has the 8222 or another SS or any of the non oil filled coils.

Does anybody know about the other FLAPS coil options? Most carry the Accel coils, but I have no idea if they will work correctly with an MSD.

I have this crazy dream of making the car go this weekend. Not likely to happen, but it sure would be nice!

-Dan

[HawgRyder]

Try asking at the local auto parts place...for a coil that goes with electronic ignition...there will be a bunch.
Or...if he has a substitute catalogue try to find a coil that equals the MSD one.
Any coil made for boosted ignition voltage (200 - 400 volts) instead of 12V should work.
As you can see, the regular type of coil has 12V input...whereas the CDI or Transistor type ignition is based on higher voltage.
If you use the 12V coil...it will either burn out the ignition module because of the resistance ( lower for the 12V type...so it draws more AMPS) or it might not put out enough voltage to fire the plugs (because of the turns ratio).
Good luck
Bob

[daniel911T]

Originally Posted by Bobboloo

Found the specs on MSD forum.

secondary resistance...4.5k
primary ---------.7 ohms

Problem solved.

Secondary resistance... 0.4ohm
Primary---------- open circuit

IMHO, that reads out of spec. Maybe... just a little... it's a marginal case... it's probably fine

I have a Blaster 2 coil in my possession that I'll be mounting somewhere in a vertical position.

I'll update the big thread to let everyone know how it goes.

Thanks for the help!

Dan