rt

In the past year, my '82 911SC has experienced 3 Bosch ignition coil failures. The two most recent within 2 weeks of each other.

Each time, it happens while I am driving the car. The engine starts stuttering (as if it is about to stall); pressing the accelerator does nothing; when I turn off the car - it won't restart. It happens after driving the vehicle around 100 miles with multiple ignition starts.

Here are the electronic specifics:
1) Stock '82 SC 3.0L - currently @ ~234K
2) Original CD unit (had previously used the Permatune CD unit); Magnecor KV85 (8.5mm) plug wires replaced stock Beru in April 2003. Engine and clutch has been fully rebuilt. Engine dropped and reinstalled multiple times; CIS separated from engine multiple times prior to 1st ignition coil failure.
3) All plugs replaced with AC Delco R42XLS @228.9K in Nov 2012
4) Replaced overcharging alternator with Bosch unit @ 229.2K in Jan 2013
5) Distributor was fully rebuilt by Partskassik in Jun 2013 @ 229.8K
6) Distributor lead wires and coil replaced by Precision Tech in 2013 @ 229.8K
(Replacement due to damage to the Permatune Coil when did partial engine drop and put engine back in.)
7) Key Ignition switch assembly (should have no impact) replaced @230K Feb 2014 by Dutch Treat.
8) New Bosch coil installed 27 Feb 2015 @ 234K by Dutch Treat
9) Coil Fails. Replaced the distributor cap & rotor with OEM Bosch; and coil wire with Beru.
10) Coil Fails 16 Mar 2015 after about 2 weeks and under 100 miles of driving.

One possible anomaly - repair shop noted that the ground strap wire to the coil mounting assembly that had been seen on an '81 SC was not present on my '82 SC. Could this be a grounding issue?

Suggestions appreciated. This has been an expensive and baffling problem.

theiceman

Bosch silver cool made in Brazil ?

If do they are junky

Go get an msd high vibration blaster coil

rt

Even a junkie coil should last longer than 100 miles. I still suspect that there is a systemic problem.

I was given the following feedback on Dorkiphus:
Is the High Tension winding failing open or shorted? Or, is the Low Tension winding failing open or shorted? (shorted is probably hard to tell). Use a ohmmeter to measure the resistance between each pair of terminals and post the results.

Here are the numbers from two bad coils, and one good Bosch coil:
1st Bad unit: 6 ohms
Most recent bad unit: 6 ohms
Working original OEM Bosch coil (loaner from the shop): 1.7 ohms

All of the coils have infinite resistance to the case. I checked the ground to the coil mounting posts, and it measured good.

Wachuko

Same issue... problem was the distributor... too much play and was damaging the coil.

Wachuko

Missed this...

Clueless...

theiceman

It's the silver coil
Mine lasted 2 hours

You asked for advice. It's up to you if you now want to take it.

Get the msd blaster coil or a used oe one from a reclaimer

wwest

The most common cause for coil failure is an open HV "circuit", ignition ARC cannot "reach" normal path so it "jumps" the next weakest point, inside the coil. Eventually a carbon path forms inside the coil and now you have permanent failure.

CDI specific coils, transformer type vs inductive where not commonplace back then, but now readily available plus inexpensive.

rt

I appreciate the feedback provided by the forum. Rather than leave you hanging, here is the path I've decided to take.

Since the vehicle was in the shop for other work (blown airbox), as well as the bad coil - I've decided to follow shop recommendations (and use the warranty on the bad coil). Thus, we went bad to full OEM - Bosch WR5DC resistor plugs vice my 2 year old AC-Delco's, and the Beru OEM plug wire set to replace the Magnecor's. Also added a ground strap from the coil negative to the fan housing that was seen on other SC's of that year.

The thoughts being that the OEM plugs, wires, cap, rotor and unfortunately Silver coil conform to the original design. The resistors at each of the elements (though creating a less intense spark) result in less loading on the coil. As insurance, the shop is lending me a Bosch "Black" coil while I drive the vehicle in this restored configuration. The last coil died after 86 miles over 6 days.

FYI - the failed coil had the following resistances:
Negative to Center pole: 655 ohms
Positive to Center pole: 655 ohms
Negative to Positive leads: 0.9 ohms (it measured 6 ohms the day before)

theiceman

my silver coil is just a paper weight

Alphasingularity

Hi, I'm new to the forum and this is my first post.

I have a 1981 SC targa since June of this year. It wasn't my first choice but after years of hunting I managed to be first in line to buy this one, so I went for it.

It's been a good car, put 10000 km's on it this summer, but there is a problem. It too is going through the coils. As part of the purchase the original owner had a Porsche dealership replace the black one (which is slightly leaking) with a silver Bosch. 700 km's into ownership, it came back on a flatbed. Shut right off at a stop light, fortunately the original owner had kept the black coil which he gave to me. It started right up. The dealership was really great about it and ordered another, which after plugging it in and driving away failed a few hours after the dealership closed and about 10 km's of use. I put the black one back in and it worked. I went on to change the cap, rotor, wires (grounded) and spark plugs and now I am waiting for a 3rd cap. While I don't know if Porsche will actually give me another cap (I'm sure they are getting annoyed), in the event they don't does the MSD coil work as a direct fit without updating the wires and CDI box? What about the "Blaster II high vibration coil", would this be even better?

The general feel I got from Porsche is that "it's the car and not the coil because it's a direct fit part".
My feeling is, if the car has done 10000 km's on an old leaky coil, then there are quality issues with the new coils being manufactured in Brasil. And while the truth may very well be somewhere in-between, the fact remains that the black coil is at the very least more tolerant to an aging car. Or my car is just telling the silver coil: auslander raus!

I have scoured the web for the past month and essentially I've come to the conclusion that two readily available coils (perma and bosch) are not a great option. And that is why I guess I'm asking the question here.

Thanks in advance.

myflat6

I had similar issues and ended up using the MSD Blaster coil. No issues since then although there are disagreements in the forum about compatability with the original CDI in our cars.

theiceman

Silver coil is Junk .. how many times do people keep insisting it cant be the coil ?? we know by a fact they can last minutes to hours.

My high vibration coil has been fine. the mH is very close along with the other specs. Has been fine . I have loaned it out to get guys home off the highway twice now as their Bosch " direct fit" silver coil has failed.

As a rule Dealerships know absolutely nothing about air cooled cars and what parts are likely to fail, they just don't see nearly enough cars to make judgments. Places like here and Pelican live and breath these issues every single day .

get a used one from a reclaimer and get on your way .

Alphasingularity

Thanks for the reply guys.

I did have my suspicion regarding the silver coil and while getting a reclaimed one is definitely an option it's one I have some apprehension with as these things are just as old as my black one. This is the reason I was really intrigued with the MSD High Vibration one. I'd really like something new and keep my old black one in the glove box as a spare.

Not to beat a dead horse but if anyone has any experience between the MSD Blaster high vibration coil (I'm assuming this is the one ICEMAN is referring to) and the Blaster II high vibration coil (newer version on the website), I would be interested in reading about it.

Thanks again.

theiceman

Actually I do the opposite .. the MSD does not look as original , so I run with my original 1978 coil and keep the blaster as a spare. I thought as you did and just wanted a back up just in case, the silver I ran with to test lasted two hours.

Alphasingularity

Makes sense. I think I will try to clean up the old one and apply a ring of epoxy to the lip where it's leaking. Maybe if I can reseal it, it can have its life extended a little.