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

This tutorial will help you determine the cause of a misfire or 'no-spark, no-start' condition on your GM car, pickup, mini-van, van or SUV equipped with a 4.3L, or 5.0L, or 5.7L engine.

The tests are explained step by step to make the whole diagnosis and troubleshooting as painless as possible.

You can use the tests in this article to test and diagnose: A bad ignition control module (ICM), or ignition coil, or a bad distributor cap, or bad spark plug wires.

A full list of GM vehicles covered by these tests is at the bottom of the page (mobile device) or on the left column (laptop/PC).

You can find this tutorial in Spanish here: Cómo Verificar El Sistema De Encendido (GM Vortec 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 The GM Distributor Mounted Ignition Module.

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

If your GM car (or pickup, van or mini-van) suffers a misfire; the check engine light (CEL) will illuminate to let you know that YES, something is indeed wrong.

Here are a few other symptoms your vehicle may experience with a misfire condition:

1. Diagnostic trouble codes (DTC) stored in the computer's (PCM) memory:
   • 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 problem in your GM car (pickup, van, SUV, or minivan), it helps to understand how spark is generated and delivered to the engine cylinders.

In short, this is what happens when you turn the key and start the engine:

1. The crankshaft position (CKP) sensor starts generating its signal and feeding it to the PCM (Powertrain Control Module = Fuel Injection Computer).
2. The PCM uses this signal to know where each piston is in relation to its combustion cycle, and with this information the PCM knows when to start activating the ignition control module (ICM), activating the injectors, and a host of other things needed to get your vehicle started.
3. After receiving the CKP signal, the PCM sends the ignition control module (ICM) a trigger signal that tells the ICM exactly when to fire the ignition coil. This trigger signal is known in GM service literature as the IC (Ignition Control) signal.
4. The ignition control module will now begin to open and close the ignition coil's primary circuit and as you may already know, it's this opening and closing action that causes the ignition coil to spark. This opening and closing process is referred to in this article as a switching signal.
5. The spark produced by the ignition coil is sent to the distributor cap via a high voltage wire and from there to each engine cylinder via a spark plug wire.

With the simple and easy tests presented in this testing article, you can find the exact cause of your vehicle's misfire or no-start problem (if it's ignition system related) while saving you time and money in the process.

Ignition System Diagnostic Manual Download

This tutorial contains a lot of information you need to diagnose and solve the ignition system problem that's causing your GM vehicle's no-start problem or misfire problem.

However, if you want access to a wiring diagram, ignition component pinouts and the entire testing procedure in one place, then take a look at the following:

Chevrolet/GMC C/K Series Full Size Pickups:

Chevrolet Express Van and GMC Savana Van:

Chevrolet Tahoe and GMC Yukon:

Chevrolet and GMC Suburban:

What Tools Do I Need To Test The Ignition System?

Although the tests in this article are simple and straightforward, you'll need some special tools to perform them. Here's the list:

1. An HEI spark tester
   • This inexpensive spark tester is a MUST HAVE for correctly diagnosing your GM vehicle's coil-on-plug ignition coils using the information and tests in this article (don't have an HEI spark tester? Need to buy one? You can buy it here: OTC 6589 Electronic Ignition Spark Tester).
   Don't use a regular spark plug instead of a spark tester.
2. Battery jump start cables.
3. A digital multimeter or analog multimeter.
4. A helper.
   • You'll need someone to help you crank the engine while you perform the tests in the engine compartment.
5. A repair manual.
   • For whatever remove and replace info you'll need that is not covered by this article.

Ignition Module Circuit Descriptions

There are 4 wires (circuits) coming out of the ignition control module (ICM) of your GM car (pickup, van, minivan or SUV).

Below are the descriptions of each circuit. Each circuit is identified by a letter, and this is the same letter found on the ignition module connector.

• Circuit labeled A -Pink (PNK) Wire:
  • Power (12 V) Circuit.
• Circuit labeled B -White (WHT) Wire:
  • Ignition Control (IC) Signal. This signal is provided courtesy of the Powertrain Control Module (PCM) and I usually refer to it as the Triggering Signal.
• Circuit labeled C -Black With White Stripe (BLK/WHT) Wire:
  • Engine Ground Circuit.
• Circuit labeled D -White With Black Stripe (WHT/BLK) Wire:
  • Switching Signal Circuit.

The following ignition system circuit diagram may be of help: Ignition System Circuit Diagram (1996-1999 Chevy/GMC Pickup And SUV).

Ignition Coil Circuit Descriptions

Your car or truck's ignition coil may or may not have 3 wires (if your vehicle has a tachometer, the ignition coil connector has 3 wires, if not, then it has 2 wires).

Whether the ignition coil connector has 2 or 3 wires doesn't matter, the information in this test article still applies. Below are the descriptions of each circuit. Each circuit is identified by a letter, and this is the same letter found on the ignition coil connector.

• Circuit labeled A -Pink (PNK) Wire:
  • Power (12 V) Circuit.
• Circuit labeled B -White (WHT) Wire:
  • Tach Signal for the Tachometer in the instrument cluster if equipped.
• Circuit labeled C -White With Black Stripe (BLK/WHT) Wire:
  • Switching Signal Circuit. This signal is provided courtesy of the ignition control module (ICM).

The following ignition system circuit diagram may be of help: Ignition System Circuit Diagram (1996-1999 Chevy/GMC Pickup And SUV).