3 fried ignition coils!! 82SC

[Kirk911SC]

So today my 82SC decided to make my day a little more interesting by quitting while I was stopped at a busy interesection.

Car has been running very well, and is driven almost everyday. No warning leading up to this.

Car just quit.........and I knew exactly what was wrong. Ignition coil AGAIN!

In fact it's the 3rd one that has quit on me in 18 months. This one lasted about 6 months. Time to call the tow truck. Luckily my mechanic was located about 1/2 mile away from the breakdown. Had him on the phone and he had a new coil there in less than an hour. Even swapped it for free! (Part under warranty from Bosch too). Checked polarity, and wiring. The two wires that attach to the coil DID have some cracked insulation at a bend. Short??

The mechanic is very experienced with Porsches, and he's puzzled by this one.

Car has relatively new cap and rotor (~10,000 miles), new plugs, and new 8.5mm Magnecor wires.

Any ideas why the coils would fail? Could a failing CDI unit cause this? Distributor problem? Alternator overcharging? (no symptoms of that).

Kirk
82SC

[75'930cab]

My 1975 911 that I sold did the same thing for the new owner. It ended up being the CDI box.

[john70t]

My guess is there is a problem with the spark getting back to ground and it's making it's own way through the windings of the coil. Seen it on a distributor cap that didn't have continuity between the button and tower.
Check the ground strap and that the plugs are all firing. Could the wires have too much resistance for the stock application and need a matching coil?

[Kirk911SC]

Hmm....grounding problem sounds like an interesting idea. I will check that out.

As for wire resistance, the Magnecores were installed because the braided wires that were on the car had HUGE resistance values. I figured they might be causing so much resistance the coil was overheating and failing. Thought my problem was solved 6 months ago....


Kirk

[Kirk911SC]

bump

[Early_S_Man]

Kirk,

Most likely scenario is that the coil was a Brazilian-made 'silver' [natural aluminum case] Bosch 0.221.121.001 coil, and they have a very, very poor reliability record!

The CDI unit can't cause coils to fail!!! I hear this myth repeated over and over here, but it simply isn't possible!!! The CDI unit puts out 350 Volt to 460 Volt pulses ... with a 1:100 turns ratio, the coil secondary attempts to develop 46 kV pulses. If there is a broken/burned carbon button inside the distributor cap that is supposed to contact the rotor, or if the rev-limiter rotor resistor is cracked or burnt 'open' ... then 'flashover' can occur inside the coil. Bosch explains the phenomenon in their test procedure booklet, which I posted a while back, here:

Perma-tune CD or Bosch CD?

[Kirk911SC]

I believe the coil is the Brazillian make, and I'll have to check the new one.........I think it probably is too!

So 3 coils failing in 1 1/2 years..........pretty pathetic quality control if you ask me. Can the German made coils still be sourced? What about a subsitute coil?

SHould I replace anything else while I'm in the area? Green wire?

Ticks me off to think that this could happen again, and with no warning too!

I guess I'm wasting my money if I put in an MSD unit?

Kirk

[Early_S_Man]

Kirk,

If the green coax has turned brown, or if it has any cracked insulation ... replace it!

The MSD epoxy-filled High-Vibration coil is a satisfactory replacement for the OEM coil, which the factory has outsourced to the Brazilian part.

MSD High-Vibration Blaster Coil $56.25 PEL-MSD-HVCOIL

[Kirk911SC]

If the green coax has failed, what typically happens? Can it cause anything else to fail? I see that the sender wire is available from P.P. What about the harness that comes off of the CDI box?

So you think all these coil failures are due to faulty manufacturing? Seems like a pretty bad reliablility record for a Bosch supplier!

I just want to prevent this from happening again. Guess I should buy an MSD coil and carry the BOsch as a spare?

Kirk

[Nitrometano]

Damn Brazilian Coil!!! MSD Vibration Coil Rules!!! I will buy one.

[Lorenfb]

"As for wire resistance, the Magnecores were installed because the braided wires that were on the car had HUGE resistance values. I figured they might be causing so much resistance the coil was overheating and failing. Thought my problem was solved 6 months ago...."

The CDI type ignition CAN"T cause a coil heating problem as an inductive discharge
system can. As mentioned, the silver Bosch coils are NOT reliable. Find an
OEM small Porsche CDI coil. They very rarely fail.

"If the green coax has failed, what typically happens? Can it cause anything else to fail? I see that the sender wire is available from P.P. What about the harness that comes off of the CDI box?"

A failure of the green wire or the distributor pickup inside can't cause anything else
to fail.

It now sounds as if we're "throwing darts" at finding the problem. So now you think
you have additional problems besides the coils? You need to do some systematic
troubleshooting.

Check out this web site (www.systemsc.com) on the Diagnostics page under No-Start.

[Early_S_Man]

Kirk,

MSD will present an even worse situation ... as the stresses on every ignition component ouside the control unit [including coil] will be higher since MSD uses 530 Volt pulses rather than pulses in the 400 Volt range. Identical coil turns ratio of 1:100 means that MSD output will be 53 kV vs 40 kV from a Bosch system!

Please examine your 'new' cap and rotor carefully ... looking for cracks, carbon tracking, and broken & blistered Glyptal sealant on the rotor over the built-in resistance element! Any eveidence of arcing is what you are looking for ... as an increased gap the spark has to jump eventually leads to a point where it is easier for the spark to 'flashover' internally than find a spark gap to ground at the spark plug!!!

A problem with the green coax means no trigger signal will be present at the CDI unit input terminal #7 and #31d ... and no high-Voltage spark will be developed at the coil output terminal!

My suggestion is to put the car on an ignition analyzer scope and looks for breakdowns [varying or degraded output pulses] indicating that the sparks are leaking to ground somewhere besides the spark plug gap.

[Superman]

I agree with Warren. At least, the parts I think I understand.