TEST 7: Testing The Pick Up Coil Signal
In TEST 6 you verified that the ignition coil isn't receiving a Switching Signal. As you might already know, this signal comes from the ignition module. Therefore, the next step is to check the module. This accomplished indirectly by checking and verifying that the pick up coil is generating a signal.
If the pick up coil's signal is present, then the ignition module is bad. If it isn't, then the reason why you're missing the Switching Signal is due to a bad pick up coil (thus exonerating the ignition control module).
This test is achieved by using a multimeter and involves installing an appropriate test lead into each of the female terminals of the pick up coil to which you'll connect the multimeter test leads (don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing). Be careful, that whatever test leads you insert into the female connectors do not damage them. Again, it's super critical that whatever you insert into these terminals doesn't open them permanently. Use common sense and take all necessary safety precautions.
IMPORTANT: The battery must be in a fully charged condition for this TEST.
These are the test steps:
Disconnect the pick up coil connector at the ignition control module. The arrow in the photo (above) points to this connector.
Connect BLACK test lead of the multimeter to one of the female terminals of the connector (using an appropriate test lead).
Connect RED test lead of multimeter to the other female terminal of the pick up coil connector.
Put the multimeter's dial in VOLTS AC mode.
In case you're wondering, it doesn't matter which terminal of the connector you insert the BLACK or RED multimeter test leads, since the polarity does not matter.
Have an assistant crank the engine while you observe the AC voltage readings on the multimeter.
As the engine is cranking, the AC voltage readings should fluctuate between 0.3 Volts and 1.8 Volts A/C. Oscilloscope users see image below of scope waveform.
Let's take a look at what your test results mean:
CASE 1: If the multimeter registered the indicated AC Volts, then the ignition control module (ICM) is bad. Replace the ignition control module.
Here's why: You have verified that the ignition module is not generating the Switching Signal in TEST 6 and by verifying that the module IS RECEIVING the pick up coil's signal in this step, you have now verified that the module is not capable of generating the Switching Signal because it's fried.
CASE 2: If the multimeter DID NOT register the indicated AC Volts (or an analog waveform such as appears in Figure 3), recheck all connections. Try again. If you still have nothing. The pick up coil is faulty and the cause of the NO START Condition. Replace the pick up coil.
TEST 8: Other Misfire Causes
There are several other things (besides a No Spark problem to a specific spark plug wire) that can cause a misfire condition on your GM vehicle.
The things that you may need to look at are:
- Carbon tracks on the spark plug and spark plug wires (see images in image viewer).
- A broken spark plug
- This usually happens when replacing the spark plugs.
- Or the engine was washed when it was Hot and the rapid cool down of the spark plug's porcelain insulator caused it to crack.
- Oil or carbon fouled spark plug or spark plugs.
- This is the result of the engine burning oil from worn out piston rings.
- Low compression in one or more engine cylinders
- You can find the test here: 4.3L, 5.0L, 5.7L Engine Compression Test (at troubleshootmyvehicle.com).
- Vacuum Leak from the intake manifold gasket.
- If your GM vehicle is the 4.3L Vortec engine (1992-1995) with the ‘Spider’ Fuel Injector set up, the Fuel Pressure Regulator could be leaking fuel inside the intake manifold plenum.
- You can find the test here: Spider Fuel Injector and Fuel Pressure Regulator Test (at troubleshootmyvehicle.com).
Where To Buy The ICM And Ignition Coil And Save
The following links will help you comparison shop for the factory original ignition control module and ignition coil:
Not sure if the ignition system components above fit your particular GM vehicle? Don't worry, once you get to the site they'll make sure they fits and if they don't, they'll find you the right ones.
If this info really saved the day, buy me a beer!