C3 Bench test for Trans. Ign. coil.....

[bruce11495]

Is there a procedure for checking the coil off the car? Is it done with an ohmmeter and is there a different reading for a TI coil versus a points coil?

[Clem Z.]

Re: C3 Bench test for Trans. Ign. coil.....

it is in the corvette shop manual and if you do not have one i will look it up.

[Dave S.]

Re: C3 Bench test for Trans. Ign. coil.....

My feeling is that the only real way to test a coil is to run it on a car. The true test is to get it nice and hot under load and see how it does.

[Jim M.]

Re: C3 Bench test for Trans. Ign. coil.....

Bruce:

Factory specs for TI coil are as follows:

Primary resistance at 75 degrees fahrenheit: 0.41-0.51 ohms
Secondary resistance at 75 degrees fahrenheit: 3000-20,000 ohms
Good luck in sorting it out.

Jim Munger #10441

[Jack H.]

Resistance specs....

are necessary but NOT sufficient to guarantee proper operation. An ignition coil is a transformer. Verifying resistance specs for primary and secondary windings on the transformer core (spec's are given in the shop manual or chassis service manual) merely tells you those wire windings are intact (NOT burned out--open circuit).

The readings do NOT tell you about the integrity of the transformer's laminated core and this is the THE device that transfers electrical engergy from the transformer's primary to its secondary windings via magnetic coupling. If the core has become de-laminated due to loss of cooling oil and/or electrical overstress, you can have correct primary/secondary resistance readings but shoddy/poor coil operation especially under the dynamics of actual operation at temperature....

Verifying the coil's primary and secondary inductance (specs are NOT published) gives you a better bench/static test since a loss of transformer core integrity will significantly reduce the value of an iron core inductor.

But, even this test (primary/secondary inductance at room temp) isn't sufficient to guarantee proper operation because the iron core's characteristics can change with temperature and rated magnetic flux circulation. Bottom line, absent a coil tester (pretty rare beastie these days), the BW to verify is to install the coil, fire the engine and monitor spark waveform(s) on an engine analyzer (most local garages have 'em)....