Plan on pulling distributor cap anyway tho to check the icm; how do you test either one ?
Connect a grounded spark tester calibrated for HEI on the DISTRIBUTOR end of the coil wire.
My favorite kind of spark-tester--one for HEI, one for points or electronic ignitions that use a ballast resistor. HEI style has a longer path for the spark--longer arc:
You must be registered for see images attach
Recessed center electrode on HEI spark tester:
You must be registered for see images attach
Remove 2-wire pickup coil connector from module. This is a pain in the tuckus on TBI distributors.
Turn on ignition.
Use a test light or jumper wire connected to battery + to touch the module terminal. There are two terminals, you want the one connected to the GREEN wire. TBI module terminals are hidden under the pickup coil, they're a real pain to get to. Every time you REMOVE the jumper wire from the module terminal, you should get a spark. The test light may or may not light up--not important. The
spark is important.
^^^ This tests the module, ignition coil, coil wire, and some of the associated vehicle wiring harness. If you DO NOT get a spark, it can be a failure of any of those components. This test does NOT verify the ECM, ECM harness, or pickup coil.
I don't have photos of doing this with a TBI distributor. The only photos I have are from the much-older 4-pin module HEIs.
You must be registered for see images attach
Alternative method--Tests pickup coil along with module, ignition coil, coil wire, and the associated vehicle wire harness:
Remove distributor cap.
Leave pickup coil CONNECTED to ignition module.
Connect grounded spark tester to DISTRIBUTOR end of coil wire.
Turn on ignition.
Get a BIG soldering iron--450 watts or bigger--and put the main body of it near the pickup coil.
Pull trigger on soldering iron for ONE SECOND. You should get a series of sparks (60, approximately) while the soldering iron trigger is pulled. Done properly, the soldering iron will not even get hot.
You must be registered for see images attach
Note that most folks don't have a big enough soldering gun.
Ideally, all this testing is done while the ignition coil is already hot from running the engine. This is not a requirement, but a recommendation.
NEITHER of these tests will verify EVERY feature of the ignition system. It will prove that the system is capable of generating strong spark, but does not verify the adaptive dwell, electronic spark advance, etc.
A module can make reliable spark, but still fail to work 100% properly.
