The GM distributor mounted ignition control module (ICM), can be tested on the car or truck easily. Not only that, you don't need any expensive tools to do it. Now, AutoZone can test it for you (if you remove it and take it to them), but for those of you that can't afford the time this involves or for those who want to add another diagnostic technique to their ‘toolbox’ of know-how, this article is for you.
This article will walk you step by step thru' the testing and diagnostic of a MISFIRE or NO-START condition. You'll test the following components: ignition control module, spark plug wires, distributor cap and rotor and ignition coil and pick up coil of the GM 4.3L, 5.0L, 5.7L and 7.4L distributor type ignition system.
Before we start, just want to remind you that since this is an on-car test, do not remove the ignition control module from the distributor or the ignition coil. Some of the images in this article show them off of the vehicle just to make it easier to explain their testing process.
Contents of this tutorial:
- Basic Operating Theory.
- Symptoms Of A Bad Ignition Control Module.
- Ignition System Diagnostic Manual Download.
- What Tools Do I Need?
- Where Do We Start?
- Ignition Module Circuit Descriptions.
- TEST 1: Testing For Spark At The Spark Plug Wires.
- TEST 2: Testing For Spark At The Distributor Cap.
- TEST 3: Testing The Ignition Coil's High Tension Wire.
- TEST 4: Testing For Spark Directly On The Ignition Coil.
- TEST 5: Testing The Ignition Coil For 12 Volts.
- TEST 6: Verifying The Ignition Coil's Switching Signal.
- TEST 7: Testing The Pick Up Coil Signal.
- Pickup Coil Waveform.
- Other Misfire Causes.
- Where To Buy The ICM And Ignition Coil And Save.
You can find this tutorial in Spanish here: Cómo Probar El Sistema De Encendido (GM 4.3L, 5.0L, 5.7L) (at: autotecnico-online.com).
The following tutorials will also help you:
- How To Test The ‘Spider’ Fuel Injector Assembly (GM 4.3L, 5.0L, 5.7L) (at: troubleshootmyvehicle.com).
- How To Diagnose Misfire Codes (GM 4.3L, 5.0L, 5.7L) (at: troubleshootmyvehicle.com).
- GM Engine Compression Test (GM 4.3L, 5.0L, 5.7L) (at: troubleshootmyvehicle.com).
- How To Test A Misfire / No Spark-No Start Condition (4.3L, 5.0L, 5.7L 96-04).
If you need to test the 7 pin (older) ignition module, the following tutorial will help: How To Test The Ignition Control Module (2.8L V6 GM).
The typical ignition system circuit diagram for the 1992-1995 4.3L, 5.0L, and 5.7L 1500, 2500, 3500 Pick Up and Suburban can be found here: Ignition System Circuit Diagram (1992-1995 Chevy/GMC Pick Up And SUV).
Basic Operating Theory
Here is a little background information (and I stress ‘little’) explained in plain English, to help you diagnose the no-start no-spark condition affecting your vehicle. In a nutshell, when you crank up the engine (and the ignition system is working properly):
- The distributor shaft starts to rotate, inducing the pick up coil to start generating its magnetic signal.
- This pick up coil signal is sent directly to the ignition control module.
- The ignition module, upon receiving this pick up coil signal (for all intended purposes it's a crankshaft position sensor signal) converts it to a digital signal that is now sent to the fuel injection computer. This digital signal is called the: Distributor Reference Hi Signal in the majority of the service literature.
- Also, after receiving the pick up coil signal, the ignition control module starts to switch the primary current (of the ignition coil) ON and OFF. As you might already know, it's this ‘Switching Signal’ that makes the ignition coil start sparking away.
- OK, once the fuel injection computer receives the Distributor Reference Hi Signal, it starts activating the fuel injectors and above 400 RPM, starts to send a 5 Volt Bypass Signal to the ignition control module. It's with the Bypass Signal that the computer starts to retard and advance ignition timing with the IC Signal.
- So, then above 400 RPM (any RPM above this and the ECM considers the engine as having started) the fuel injection computer starts to control the ignition timing.
The tests that you're gonna' learn in this article only deal with steps 1 thru' 4, among several tests. But whether your car or truck does not start or starts but runs with a misfire, this is the tutorial you need to diagnose it!
Symptoms Of A Bad Ignition Control Module
The following are usually the most common symptoms of a bad ignition control module on this type of GM distributor mounted ignition control module:
- The car (or truck, or mini-van, or van) will crank but not start.
- No spark coming from any of the spark plug wires.
- The throttle body fuel injectors do not spray gasoline.
The following are usually the most common symptoms of a bad spark plug wires, or a bad distributor cap and rotor on this type of GM distributor mounted ignition control module:
- The car (or truck, or mini-van, or van) starts and runs, but with a misfire.
- The check engine light is on.
- Lack of power.
- Rough idle.
- Bad gas mileage.
- Rotten egg smell coming out of the tailpipe.
- Black smoke coming out of the tailpipe.
- Won't pass the mandatory state emissions test.
The following is usually the most common (and only) symptom of a bad ignition coil on this type of GM distributor mounted ignition control module:
- The car (or truck, or mini-van, or van) cranks but does not start.
Ignition System Diagnostic Manual Download
This tutorial has a lot of the information you'll need to diagnose and solve the ignition system problem causing your GM vehicle's no-start problem.
But, if you'd like to have access to a wiring diagram, ignition component connector pin-outs, and the entire testing procedure in one place, then take a look at the following:
1992-1995 4.3L Astro/Safari
Ignition System No-Start Problem Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a no-start problem caused by the ignition module, or the ignition coil, or the distributor pickup coil.
Diagnostic manual comes with:
- Wiring diagram.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing orders.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly!
Chevrolet/GMC C/K Series Pick Ups:
Engines: 4.3L, 5.0L, 5.7L, 7.4L
1992 Full Size Pick Up
Ignition System No-Start Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a no-start problem caused by the ignition module, or the ignition coil, or the distributor pickup coil.
Diagnostic manual comes with:
- Wiring diagram.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing orders.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly! Applies to:
- 1992 Chevrolet C1500, C2500, C3500 Pick Up.
- 1992 Chevrolet K1500, K2500, K3500 Pick Up.
- 1992 GMC C1500, C2500, C3500 Pick Up.
- 1992 GMC K1500, K2500, K3500 Pick Up.
Engines: 4.3L, 5.0L, 5.7L, 7.4L
1993 Full Size Pick Up
Ignition System No-Start Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a no-start problem caused by the ignition module, or the ignition coil, or the distributor pickup coil.
Diagnostic manual comes with:
- Wiring diagram.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing orders.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly! Applies to:
- 1993 Chevrolet C1500, C2500, C3500 Pick Up.
- 1993 Chevrolet K1500, K2500, K3500 Pick Up.
- 1993 GMC C1500, C2500, C3500 Pick Up.
- 1993 GMC K1500, K2500, K3500 Pick Up.
Engines: 4.3L, 5.0L, 5.7L, 7.4L
1994 Full Size Pick Up
Ignition System No-Start Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a no-start problem caused by the ignition module, or the ignition coil, or the distributor pickup coil.
Diagnostic manual comes with:
- Wiring diagram.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing orders.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly! Applies to:
- 1994 Chevrolet C1500, C2500, C3500 Pick Up.
- 1994 Chevrolet K1500, K2500, K3500 Pick Up.
- 1994 GMC C1500, C2500, C3500 Pick Up.
- 1994 GMC K1500, K2500, K3500 Pick Up.
Engines: 4.3L, 5.0L, 5.7L, 7.4L
1995 Full Size Pick Up
Ignition System No-Start Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a no-start problem caused by the ignition module, or the ignition coil, or the distributor pickup coil.
Diagnostic manual comes with:
- Wiring diagram.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing orders.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly! Applies to:
- 1995 Chevrolet C1500, C2500, C3500 Pick Up.
- 1995 Chevrolet K1500, K2500, K3500 Pick Up.
- 1995 GMC C1500, C2500, C3500 Pick Up.
- 1995 GMC K1500, K2500, K3500 Pick Up.
Chevrolet/GMC G-Series Full-Size Van:
Engines: 4.3L, 5.0L, 5.7L, 7.4L
1992 G Series Van
Ignition System No-Start Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a misfire or a no-start problem (caused by the ignition module, the ignition coil, or the pickup coil).
Diagnostic manual comes with:
- Wiring diagrams.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing orders.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly! Applies to:
- 1992 Chevrolet G10, G20, G30.
- 1992 GMC G1500, G2500, G3500.
Engines: 4.3L, 5.0L, 5.7L, 7.4L
1993 G Series Van
Ignition System No-Start Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a misfire or a no-start problem (caused by the ignition module, the ignition coil, or the pickup coil).
Diagnostic manual comes with:
- Wiring diagrams.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing orders.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly! Applies to:
- 1993 Chevrolet G10, G20, G30.
- 1993 GMC G1500, G2500, G3500.
Engines: 4.3L, 5.0L, 5.7L, 7.4L
1994 G Series Van
Ignition System No-Start Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a misfire or a no-start problem (caused by the ignition module, the ignition coil, or the pickup coil).
Diagnostic manual comes with:
- Wiring diagrams.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing orders.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly! Applies to:
- 1994 Chevrolet G10, G20, G30.
- 1994 GMC G1500, G2500, G3500.
Engines: 4.3L, 5.0L, 5.7L, 7.4L
1995 G Series Van
Ignition System No-Start Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a misfire or a no-start problem (caused by the ignition module, the ignition coil, or the pickup coil).
Diagnostic manual comes with:
- Wiring diagrams.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing orders.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly! Applies to:
- 1995 Chevrolet G10, G20, G30.
- 1995 GMC G1500, G2500, G3500.
Chevrolet Tahoe and GMC Yukon:
Engines: 5.7L
1995 Tahoe/Yukon
Ignition System No-Start Diagnostic Manual
$3.99 USD
All of the information you need to diagnose a misfire or a no-start problem (caused by the ignition module or the ignition coil).
Diagnostic manual comes with:
- Wiring diagram.
- Component pin outs.
- Connector pin outs.
- Ignition system component part numbers.
- Firing order.
- Complete step-by-step testing instructions.
The illustrations in the diagnostic manual are printer friendly! Applies to:
- 1995 Chevrolet Tahoe (4x2 and 4x4).
- 1995 GMC Yukon (4x2 and 4x4).
