How To Test A Misfire / No Spark-No Start Condition (4.3L, 5.0L, 5.7L 96-04) How To Test A Misfire / No Spark-No Start Condition (4.3L, 5.0L, 5.7L 96-04)

This article will help you to find the cause of a misfire or No Spark- No Start Condition on your GM car, pick up, mini-van, van or SUV equipped with a 4.3L, or 5.0L, or 5.7L engine. The testing is explained step by step, making the whole diagnostic and troubleshooting as pain free as possible.

With the tests in this article, you'll be able to test and diagnose: A BAD ignition control module, or a BAD ignition coil, or a BAD distributor cap, or BAD spark plug wires. For a complete list of GM vehicles these tests apply to, take a look at the bottom of the page.

The following tutorials will also help you:

  1. How To Test The ‘Spider’ Fuel Injector Assembly (GM 4.3L, 5.0L, 5.7L) (at:
  2. How To Diagnose Misfire Codes (GM 4.3L, 5.0L, 5.7L) (at:
  3. GM Engine Compression Test (GM 4.3L, 5.0L, 5.7L) (at:
  4. How To Test The GM Distributor Mounted Ignition Module.

You can find this tutorial in Spanish here: Cómo Verificar el Sistema de Encendido (GM Vortec 4.3L, 5.0L, 5.7L) (at:

Symptoms Of A BAD ICM, Ignition Coil, Spark Plug Wires, Or Dist. Cap

If your GM car (or pick up, van , or mini-van) is suffering a misfire; the check engine light (CEL) will be on to let you know that YES, there really is something wrong. Here are a couple of other symptoms your vehicle may experience with a misfire condition:

  1. Diagnostic trouble codes (DTC) stored in the computer's (PCM) memory:
    1. P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308
  2. Misfire that does not light up the check engine light (CEL).
  3. No power.
  4. Idles rough.
  5. BAD gas mileage.
  6. Black smoke coming out of the tail pipe.
  7. Rotten egg smell coming out of the tail pipe.
  8. Smell of unburned gasoline coming out of the tail pipe.
  9. Won't pass the state emissions test.
  10. Cranks but doesn't start.

Basic GM Ignition System Theory

To successfully diagnose a Misfire or No Start on your GM car (pick up, van, SUV, or mini-van) it'll help to know how spark is created and fed to the engine cylinders. This is what happens, in a nutshell, when you turn the key and crank the engine:

  1. The crankshaft position sensor starts to generate and feed the PCM (Powertrain Control Module=Fuel Injection Computer) with its signal.
  2. The PCM uses this signal to know where each Piston is at in relation to its combustion cycle and with this info, the PCM knows when to start activating the ignition control module (ICM), activating the fuel injectors and a host of other things to get your vehicle started.
  3. So then, after receiving the crank (CKP) signal, the PCM sends the ignition control module (ICM) a Triggering Signal that tells the ICM exactly when to make the ignition coil spark. This Triggering Signal is known as the IC (Ignition Control) Signal in the GM service literature.
  4. The ignition control module now starts to open and close the primary current circuit of the ignition coil and as you may already be aware, it's this opening and closing action that makes the ignition coil spark away. This opening and closing action is referred to as the Switching Signal in this article.
  5. The spark created by the ignition coil is fed to the distributor cap by a high tension wire and from there to each engine cylinder by a spark plug wire.

With the simple and easy tests presented in this test article you'll be able to find the exact cause of your vehicle's misfire or no start condition (if it's ignition system related) and in the process save time and money.