TEST 2: Verifying The Ignition Coil Activation Signal
In this test section, we're going to make sure that the ignition control module (ICM) is creating the ignition coil's activation signal. This activation signal is what makes the ignition coil to start sparking away.
If this test confirms that the activation signal is present, then we can conclude that the (ICM) is OK and doing its job. But if this signal is missing, then the next step is to check that the ignition control module is getting the crankshaft position signal from the pickup coil.
NOTE: This test section requires that you crank the engine as you check for the ignition coil's activation signal. For this reason, it's important that the battery be fully charged. If the battery is low on charge, charge it up fully before you start.
OK, these are the test steps:
- 1
Connect the 12 Volt test light's crocodile type connector to the battery positive (+) terminal.
- 2
Connect the metal point of the 12 Volt test light to the white (WHT) wire of the black connector.
The WHT wire connects to the terminal labeled "Signal" in the image above.
The WHT wire connects directly to the ignition control module and the is the one that delivers the ignition coil activation signal. - 3
Have your helper crank the engine while you observe the 12 Volt test light.
- 4
You'll see one of two things as the engine is cranking:
1.) The 12 Volt test light flashes ON and OFF.
2.) The 12 Volt test light DOES NOT flash ON and OFF
Alright, let's take a look at what your test results mean:
CASE 1: The 12 Volt test light flashed ON and OFF as your helper cranked the engine. This is means that the ignition control module is activating the ignition coil.
This test result also let you know that the pickup coil is OK. In other words the pickup coil is providing the crankshaft position signal to the ignition module and thus is not defective.
Since you're troubleshooting a cranks but does not start issue, the following tutorial may help:
CASE 2: The 12 Volt test light DID NOT flash ON and OFF as your helper cranked the engine. This test result tells you that the ignition control module is not activating the ignition coil.
The most likely cause of this missing activation signal is either a bad ignition control module (ICM) or a bad pick-up coil (which is the crank sensor). Your next step is to check the pickup coil's signal. For this test go to: TEST 3: Verifying The Pickup Coil's Signal.
TEST 3: Verifying The Pickup Coil's Signal
As I mentioned at the beginning of this tutorial, the pickup coil is the de facto crankshaft position sensor. So, in this test section we're going to make sure that it's creating a crankshaft position signal.
If the pickup coil's crankshaft position signal is not present, the ignition control module (ICM) will not activate the ignition coil (to start sparking away) and it also won't let the fuel injection computer know that it's time to start injecting fuel into the engine.
IMPORTANT: This test requires that you test the pickup coil signal with the engine cranking. For this reason you must take all necessary safety precautions and think safety all of the time. I strongly suggest that you use back probes to connect your multimeter to the pickup coil's connector and be able to read your multimeter from a safe distance during the test.
OK, these are the test steps:
- 1
Remove the distributor cap from the ignition distributor. The pickup coil is located inside the distributor.
- 2
Disconnect the pickup coil from the ignition control module.
- 3
Connect the black test lead of the multimeter to one of the female terminals of the connector (using an appropriate test lead).
It doesn't matter which multimeter test lead you use, the red or black one, as the polarity of the terminal does not affect the outcome of the test.
IMPORTANT: Do not insert the multimeter test leads into the pickup coil's female terminals, or you'll damage them. - 4
Connect the red test lead of multimeter to the other female terminal of the pickup coil connector..
- 5
Place your multimeter in Volts AC mode.
The pickup coil creates a voltage AC signal that can be easily read with your multimeter in Volts AC mode. - 6
When the multimeter is set up, have your helper crank the engine. As the engine is turning over, observe your multimeter from a safe distance.
- 7
As the engine is cranking, your multimeter should read a voltage between 0.3 to 1.8 Volts AC.
NOTE: This voltage will fluctuate between these two values.
Alright, let's take a look at what your test results mean:
CASE 1: Your multimeter registered a voltage between 0.3 to 1.8 Volts AC as the engine was cranking. This test result tells you that the ignition pickup coil is creating a crankshaft position signal.
You can conclude that the ignition control module is bad (and needs replacement) if you have confirmed all of the following:
- The ignition coil is not sparking.
- The ignition control module (ICM) is getting power in the form of 10 to 12 Volts DC (TEST 1).
- The ignition control module is not activating the ignition coil (TEST 2).
- The pickup coil is creating a crankshaft position signal (this test).
CASE 2: Your multimeter DID NOT register a voltage between 0.3 to 1.8 Volts AC as the engine was cranking. This test result lets you know that the ignition control module is bad.
Without this crankshaft position signal, the ignition control module (ICM) will not activate the ignition coil to start sparking. The ignition module also will not inform the fuel injection computer that it's time to start injecting fuel.
Replacing the ignition pickup coil will get your vehicle back on the road. Take a look at the section: Where To Buy The Ignition Control Module And Save.
More 2.8L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials
You can find a complete list of tutorials for the 2.8L V6 Chevrolet S10 pickup, GMC S15 pickup, and GMC Sonoma in this index:
Here's a sample of the articles, you'll find in the Index of Articles:
- How To Test The Fuel Pump (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test Engine Compression (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The EGR Valve (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The Starter Motor (1988-1993 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup).
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