What Tools Do I Need?

The most important tool that you're gonna' need is a digital multimeter (don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing). You can use an Analog one but, the digital one is preferred. If you don't have one, you don't have to buy anything expensive and/or fancy since you only need the multimeter to measure the AC Voltage signal of the pick up coil.

You can also use an oscilloscope if you have one... now since so few folks have one, this article concentrates on using simple everyday tools to accomplish the tests. Although, if you have access to an oscilloscope, I have included a scope pattern of what the signal waveform should look like (in TEST 7).

The other MUST HAVE tool is an LED light. You'll use this tool to test for the ignition coil's Switching Signal. If you don't own an LED light, you can buy one from any electronics store ( I buy mine from my local Radio Shack store) or from your local auto parts store (like AutoZone, O'reilly, Pepboys, etc). Want to see what this tool looks like? Click here: Abe's LED Light Tool.

And the last MUST HAVE tool is an HEI Spark Tester. The foundation of this test article is the HEI spark tester. If you don't have one, I recommend that you buy one (don't have an HEI spark tester? Need to buy one? You can buy it here: OTC 6589 Electronic Ignition Spark Tester)

Where Do We Start?

We'll first check for the basics like:

  1. Spark.
  2. Battery voltage at both the ignition coil and ignition control module.
  3. Then we'll check that the ignition control module is triggering the ignition coil.
  4. Next, we'll verify that the ignition control module (ICM) is receiving the signal from the pick up coil.

From the results you get, you'll be able to pinpoint the problem to the ignition control module or the ignition coil or the pick up coil or completely eliminate these as the cause of the no start condition.

IMPORTANT: All of the tests are ON CAR TESTS, do not remove the ignition control module (ICM) from the distributor (all of the figures show the ignition control module off of the distributor but this is just for illustration purposes only).

Ignition Module Circuit Descriptions

Ignition Module Circuit Descriptions. How To Test The GM Distributor Mounted Ignition Module

In the above figure you'll notice that the ignition control module (ICM) has three connectors. I have labeled the connectors 1 thru' 3. Only the circuits of connectors 1 and 3 are going to figure in on our tests, but I have included some circuit descriptions for connector 2.

IMPORTANT: battery must be in a fully charged state for all tests. All tests are done with the ignition coil and ignition control module (ICM) connected to all of their respective connectors unless otherwise specified in the tests below. Since you'll be working around a cranking engine, be careful, use common sense and take all necessary safety precautions.

Connector 1

  1. +- PINK (or PINK with BLACK stripe) wire.
    1. 12 Volts with Ignition ON.
  2. C- WHITE wire.
    1. IGNITION COIL control pulses.

Connector 2

  1. G- BLACK with RED stripe (or RED with BLACK stripe) wire.
    1. Ground circuit for ECM.
  2. B- TAN with BLACK stripe wire.
    1. 5 Volt Reference from ECM (above 400 RPM).
  3. R- PURPLE with WHITE stripe wire.
    1. Fuel control circuit.
  4. E- WHITE wire.
    1. ECM control signal of ignition module (above 400 RPM).

Connector 3

  1. P- GREEN wire.
    1. CKP Sensor Signal Circuit (PICK UP COIL).
  2. N- YELLOW wire.
    1. CKP Sensor Signal Circuit (PICK UP COIL).

Now, don't worry, it's not necessary to check every single wires' signal to test the ignition control module. All right, lets get started!