evozine

How long do ignition coils remain fully operational...? My 84s has a blue coil that looks original, making it 24 years old...
The car runs quite well for an older model, although the coil has a small plastic piece missing from the very top.

thanks

RyanPerrella

I heard recently that coils need to be sitting with the posts level and or slightly below the center point. Apparently some fluid inside the coils can dry up and lead to a dead coil.

Because of this i checked mine and adjusted one of them to comply with this idea. Anyone else every heard of this?

evozine

Anyone, Anyone...., Bueller.....?

RyanPerrella

assume 20 years

maybe you can take it to autozone, they test damn near anything for free. Not sure if they can test coils though, but i dont see why not.

evozine

Thanks Ryan..,

Angel84-928

Don't take it to Autozone. Break out your Multimeter and test it yourself. Here is a linky: Why Bench Test Your Ignition Coil?

WSM Section 28 pg 28-13 gives you the steps on how to test.

Ignition Coil Primary .33 - .46 ohms
Ignition Coil Secondary 7 - 12k ohms

RyanPerrella

THERE YOU GO! ^^^^^^^

nice link EDIT REAL NICE LINK! Great info here.

Angel84-928

Ryan P

leperboy

They do test coils. But do the home test. The quality of Autozone technician varies wildly from incompetent to minimally competent.

Matt

RyanPerrella

I agree 100% about the quality of the autozone techs......

But, i was hoping the test would be like the battery test where they just need to know how to hook up the two ends and the machine tells them CLEARLY either PASS or FAIL. If they need to read numbers and see if they are within spec, then yeah that could be too difficult for them.

Panzer9

I think I'll do just that. Thanks

dr bob

There's the basic resistance test that's shared here, and there's an insulation breakdown test that is tough to do. Autozone doesn't do it.

IIRC, the Bosch 'blue' coils were supposedly a higher-output replacement, originally intended for non-electronic ignition systems. Check the label to see if it's what your car deserves. I don't think there were any blue OEM-installed Bosch coils.

Generally, when you do all the simple tests, have the correct voltage and signals, and your car won't start, then you might consider coil failure as a possibility. In my early formative high-school years I sold auto parts at a neighborhood store. Customer would buy a coil, convinced that their's was bad. Wth only a very few exceptions, the new one was brought back because it didn't solve the problem or "because it was defective". I rigged up a little test fixture with an old distributor and a battery, so we could do functional testing of customers' ignition coils. It was a good demo if nothing else. If a customer really insisted that the coil they bought was defective, I'd plug it into the tester and ask the customer to hold the hi-tension lead while I spun the distributor. Nobody wanted to, for some reason.

Failure mode on coils is generally hi-tension insulation breakdown. It happens when the output voltage isn't limited by a spark plug connected to its output. A disconnected wire, a worn or broken cap or rotor, or a worn-out set of plugs will hasten the demise of an otherwise bulletproof coil. Testing for spark while holding a plug wire an inch from ground is another way. The voltage that builds up in the coil may arc through the insulation internally before it can make the jumps through all the gaps. Once the internal insulation has arc-through damage it will forever be weak there.

As Ryan points out, there's oil in the coil do distribute heat out from the windings through the casing. I guess if the oil level inside was a little low, the nose-down mounting position issue might become important; Otherwise they can be mounted in any orientation safely.


HTH!

RyanPerrella

Good info Bob

Glad to know there actually is oil in there. Previously i just thought all an ignition coil was was some "magic mud" stuffed in a nice cylindrical package that makes nice sparks! Kinda like the "Magical underpants" that are popular in Utah.

Dennis Wilson

Another life shortener is constant cranking. This puts a higher voltage through the coil to achieve a hotter spark. This isn't as obvious on the 928 since there should never be 12 volts going to the coil during cranking, as most other cars, but over time it can overheat and fry the coil.

Dennis

dr bob

Early cars do in fact have a "ballast" or "dropping resistor" in series with the coil, bypassed during cranking. Idea is that cranking draws down the battery voltage enough to need an extra bit of ooomph.. Once you release the starter, current again flows through the resistor. Unless something is changed, the coil still never sees full unloaded battery voltage.

The big Killer of coils is really vibration. Maybe not an issue on our cars, but... Vibration causes the internal windings to rub against one another until the insulation fails. I can also say with conviction that they don't like to be dropped. At all.