I have two used 122 coils - what is the best way to test them? I'd like to know which one might have the most life left in it. I'm familiar with the old 'color of the spark at night' test (blue=good, yellow=bad), but is can they be tested (quantitatively) without wiring them up to the car? Is there such a thing as a "coil tester"?

http://www.international-auto.com/tbcoil.html

FYI: The Volvo service manual I have from 1966 (which gives pages on how to rebuild a generator as well as Herr Bosch himself) gives only a generic description of what a coil is/does. Apparently, there must have been a factory document with more info.: envision a closely-guarded booklet titled "Secrets of the Armoured Coil"!!!

Thanks for this procedure Shayne - Given that Volvo 122 (and 1800?) coils have only one small terminal on top (instead of the two on the diagram), can one of you electro-wizz guys tell me which terminal on the back of the ignition switch would correspond to the "missing" second coil terminal?

Vovo;

There is NONE which corresponds!...think about it...what is point of the armoured cable in the first place?...if that terminal was moved to the back of the IGN switch, you could hot wire the car from there. The coil hot wire in not available on the outside of the assembly...

....and, there is nothing "secret" happening withing the assembly...just because its protected shouldn't lead you to think that...its a standard, non-ballast, points type ignition system, period...test as previously described!

Cheers

I just ordered a Pertronix to go on my new 142. I had a look at the instructions last night and I think that it said the coil had to have a resistance of at least 3ohm. That doesn't gell with the test. Maybe my old age memory is getting to me and it said 'no more than 3 ohm'? I'll check tonight.

If it fails that test, it's certainly bad, but if it passes, it may still not be good.

How hard is it to install a coil (even with the switch attached)? I'd say try one out and keep the other for a spare.

Guys;

That link shows how to test typical (three terminal) coils, stating: "...testing procedure is valid for just about any automotive coil".

What it should say in addition to that is: ...EXCEPT for vintage Volvo coils, which require no ballast resistor, and are permanently connected by way of an armoured cable, to the ignition switch. Because of this, the resistances indicated are hardly what I would expect, even if you could get to some of the connections.

IMO, the best way to check them (short of test-installing them into a car), is to wire them up to a battery per a 122 wiring diagram, an to put the output on a spark-plug (no distributor required, but substitute a momentary pushbutton for the points).

Cheers

Ron, good reality check... 8^)

Just for the record, the Bosch "blue" coils commonly used as generic replacements also have built-in ballasts and would fail those resistance tests.

Hi Gang, My coil is hot, what's up with that? Anything to be done, or maybe I got something hooked up wrong. Thanks, Keith

Keith;

If the coil is warm, even very warm, but still works as it should, not to worry. Ignition coils are just that...a coil of wire...actually two (primary and secondary), and they will generate a certain amount of heat during use when power is applied and interrupted continuously to generate spark.

If however you turn your IGN ON for some reason, and leave it ON without running the motor for a while (to do underhood servicing or some such thing), and the points happen to be closed, the primary coil will have a continuous 12V applied and I expect will get pretty toasty. There's nothing wrong with turning IGN ON and doing servicing with motor not running, but for the sake of your coil, avoid doing this for an extended time.

Cheers

Guys;

I question the usefulness of resistance tests for checking an ignition coil in the first place. About the only thing an Ohmmeter check could be usefull for is to check if it is a coil requiring a ballast resistor or not, because with few exceptions, the failure mode of almost any ignition coil is an insulation breakdown due to (and only WHEN) the high voltage is generated. The low voltage that an Ohmmeter uses to test resistance will not breakdown the insulation, so I'd bet a hot fudge sundae that 9 out of 10 failed coils will even check out fine, using an Ohmmeter.

To elaborate on a more useful test...hook up per 122 wiring diagram, using a pushbutton in place of the points, and open up the sparkplug gap to double the normal .032". If you get a healthy spark jumping across that gap, you can have a pretty good level of confidence that its a keeper! (CYA Note: Coil may STILL fail when it gets hot!) Variations on this technique also work well to non-lethaly discourage squirrels which insist the bird feeder is just for them...hehehe...after the second lesson, they don't dare!

Cheers