3 Bad Ignition Control Module Symptoms: How It Goes Bad?

Are you tired of feeling like you’re in a constant battle with your car’s engine? Maybe you’re experiencing engine stalls, misfires, or strange behavior that has you wondering what’s going on under the hood. Or perhaps you’re even struggling to start your vehicle altogether. Before you throw in the towel and assume it’s time to trade in your ride, consider the possibility that it could be a faulty ignition control module (ICM) causing all the trouble.

Just last week, my neighbor was stressing out over their car’s engine misfires, which turned out to be caused by a bad ICM. So, in this article, we’ll delve into the topic of bad ignition control module symptoms. We’ll cover everything from the common signs of a failing ignition control module to the potential risks of ignoring them. 

So, what are the symptoms of a bad ignition control module? A bad ignition control module can cause a variety of symptoms in a vehicle. One of the most common symptoms is engine misfires, which can cause the engine to run rough, stall, or hesitate during acceleration. Other symptoms include difficulty starting the engine, poor fuel economy, and a check engine light that stays on. In some cases, the vehicle may not start at all. When diagnosing a bad ignition control module, it is important to check the spark plugs and wires, as well as the distributor cap and rotor. These components can also cause similar symptoms if they are worn or damaged. 

What Exactly Is Ignition Control Module?

Ignition Control Module, also known as ICM, is an electronic device that is used in vehicles to control the ignition system. It is responsible for regulating the timing and firing of the spark plugs, which in turn ignites the fuel in the engine. The main purpose of the ICM is to ensure that the engine runs smoothly and efficiently.

The location of the ICM varies depending on your vehicle’s ignition system. Some common locations are:

  • Inside or near the distributor
  • On or near the ignition coil
  • On or near the firewall

The ICM worked by receiving signals from the engine’s sensors (crankshaft position sensor, camshaft sensor and MAP sensor), and using that information to determine the appropriate timing for the ignition system. This process occurs repeatedly as the engine runs, ensuring that the ignition system is functioning properly and the engine is running as smoothly as possible.

The ICM is also responsible for controlling the dwell time, which is the duration the ignition coil is charged before it discharges its energy in the form of a spark. The spark ignites the fuel-air mixture in the engine, allowing it to combust and produce power. 

Keep in mind that the ignition control module only controls the current flow to the primary coil of the ignition coil/distributor. This is the 12V current that flows straight from the battery and controlled by the ICM. The ignition coil or distributor then magnifies this current to thousands of volts to generate a spark.

Ignition Control Module Variations

The early ignition control modules used to be simple switches that could turn on and off only. They worked when a magnetic pulse pickup coil in the distributor triggered them.

The distributor pickup consists of a rotating reluctor and a stationary pick-up coil with a magnet. The reluctor is a wheel with evenly spaced teeth that rotates with the distributor shaft. The number of teeth on the reluctor is equal to the number of cylinders in an engine.

The pick-up coil surrounds the reluctor and contains a permanent magnet. As the reluctor spins, the teeth on the wheel pass by the pick-up coil, causing fluctuations in the magnetic field around the coil. These fluctuations generate electrical pulses, which are sent to the ignition control module, triggering the ignition coil to fire. 

If you want to know about the difference between contactless and electronic distributors, you can watch the following video:

Later on, computerized engine controls were made and the ignition module’s design was changed.

The new design had a square-wave signal sent to the engine control module (ECM), after which the ECM would calculate how much spark advance was needed for the engine operating conditions. The ECM then sent a square-wave signal back to the ignition module to trigger the spark to start the engine.

As operations become more complex, the module is often moved from the inside of the distributor to cooler locations like an engine compartment fender well. 

In more late-model instances, the ignition module is integrated into the powertrain control module (PCM), also called ECU, itself to simplify system electronics.

Here is a simpler arrow diagram of how ignition control modules transformed with time:

“Magnetic pulse coil in distributor” -> “Simple on-off switches” -> “Computerized engine controls” -> “Signal sent to ECM” -> “ECM calculates spark advance” -> “Signal sent to ignition module” -> “Trigger spark” -> “Module moved to cooler locations”/”Integrated into coil pack” -> “Integrated into PCM”

Ignition Timing In Electronic Distributor Modules

The mechanical advance mechanism in an electronic distributor advances the ignition timing as the engine’s RPM increases. The mechanical advance’s function is to adjust the timing of the spark plug in relation to the piston’s position in the cylinder. 

In a mechanical advance system, there are two main components: the flyweights and the spring. The flyweights are attached to the distributor shaft and spin as the engine revs up. As the flyweights spin, they are pushed outwards by centrifugal force. This movement compresses the spring, which in turn resists this movement, creating a balancing effect.

The movement of the flyweights rotates the trigger mechanism (reluctor wheel mounted on distributor shaft), which will advance the ignition timing.

The tension of the spring determines the rate at which the mechanical advance occurs. Different springs can be used to achieve different rates of advance. A stiffer spring will require higher engine speeds to overcome its resistance and initiate the advance, resulting in a delayed timing advance.

The vacuum advance mechanism in an electronic distributor adjusts the ignition timing based on the engine’s vacuum. The vacuum advance mechanism consists of a diaphragm, a spring, and a vacuum chamber. The vacuum chamber is connected to the intake manifold through a hose, and the spring keeps the diaphragm in a neutral position.

When the engine is running, the vacuum from the engine pulls on the diaphragm, which in turn rotates the distributor shaft, advancing the timing of the spark.

Point to ponder: The mechanical and vacuum advance systems work together to provide optimal timing for the spark. At low engine speeds, the vacuum advance system is responsible for advancing the timing of the spark. As the engine speed increases, the mechanical advance system takes over, advancing the timing of the spark even further. The combination of the two systems allows for precise spark timing throughout the entire range of engine speeds. 

How Does Ignition Control Module Go Bad?

Here are the factors due to which an ignition control module can go bad:

  • Overheating: The ignition control module is located near the engine, making it susceptible to heat damage. Over time, exposure to high temperatures can cause the module’s electrical components to deteriorate, leading to a malfunction.
  • Moisture: Moisture can cause electrical components to short circuit, leading to ignition control module failure. Moisture can enter the module through cracks, damaged wires, or faulty seals in the distributor cap.
  • Wear and Tear: Like other car components, the ignition control module can wear out over time. The constant exposure to electrical current and heat can cause the module’s electronic components, including pick-up coil, to break down, leading to a malfunction. Moreover, the ignition control module is exposed to vibrations, which can cause the electronic components to loosen or break. 
  • Voltage Spikes:  Ignition modules need a full 12 volts supplied and a good ground to function properly. A voltage spike occurs when the electrical system experiences a sudden increase in voltage. This can happen when the alternator fails, the battery is overcharged, or when there is a problem with the electrical wiring. It will cause an electrical surge to flow through the ignition control module. This surge can damage the module’s electronic components, leading to failure.
  • Distributor Pickup Failure: In contactless distributors, the bushing area gets worn out which causes the shaft to move sideways. This sideways movement leads to the reluctor points on the shaft striking the points on the pickup coil pole piece. When this happens, the ECM is unable to receive a proper signal for RPM and timing, leading to timing issues and eventually engine misfires.
  • Poor Electrical Connections: Poor electrical connections can also cause the ICM to fail. Dirt, grime, and other debris can accumulate on the ICM’s electrical connectors, causing them to fail. 
  • Insulation of Wires Is Damaged: The wiring that connects the ICM to the rest of the ignition system is protected by a layer of insulation. Over time, this insulation can become damaged due to exposure to heat, moisture, and other environmental factors. When the insulation is compromised, the wiring can come into contact with other metal components, causing a short circuit randomly.
  • Loss of Magnetism: One of the common reasons why the ignition control module becomes bad is due to the loss of magnetism of the magnet around the pickup coil. The magnetic field is an essential component of the ignition system, as it generates the voltage that creates the spark. Over time, the magnet around the pickup coil can lose its magnetism, resulting in a weak or no spark. This can be caused by various factors, including exposure to extreme temperatures, wear and tear, and poor maintenance practices.

Spark Advance In 350 TBI Engines

350 TBI engines also have ignition control module inside the distributor. But, it has no role when engine is running at higher RPMs.

The 350 TBI engines have EST (Electronic Spark Timing) ignition system. The distributor of EST ignition system in 350 TBI engines does not have mechanical or vacuum advance.

In EST electronic distributors, an electric spark timing module is mounted in the distributors that receives signals from the engine control module (ECM) to advance the ignition timing. So, in these systems, all spark timing changes are controlled electronically. In simple words, EST is the advanced version of ignition control module.

Many people also confuse ESC with ETC. ESC (Electronic Spark Control) is something else. It is not inside the distributor. The ESC only signals the ECM to retard the ignition timing (which the ECM signals to the EST in turn). It pulls out the ignition timing to get rid of the knocking.

In some models, the ESC module lies on the bracket along with the EGR solenoid, the passenger side of the TBI. The module is mostly flat. In some vehicles, the ESC module is mounted on the firewall directly behind the air cleaner. You will still find that bracket with the space for the ESC but it would be blank other than the EGR solenoid.

In later models after 1993, ESC module has been integrated into the ECM.

Bad Ignition Control Module Symptoms

1. Car Won’t Start or Has Difficulty In Starting

A bad ICM can cause several symptoms, and some of the most common symptoms are difficulty in starting the car or a complete failure to start. When the ICM fails, it can prevent the spark plugs from firing, which means that the fuel in the engine will not ignite. This can cause the engine to crank but not start or fail to crank at all. 

2. Bad Fuel Economy and Poor Engine Performance

A faulty ICM can lead to a range of engine performance issues, including poor fuel economy and reduced power output.

When your ignition control module is failing, it can cause your engine to misfire. This means that your engine is not firing on all cylinders, resulting in reduced power output and increased fuel consumption. 

3. Engine Misfire Codes and Check Engine Light

A bad ICM can cause the engine to misfire, which will trigger the Check Engine Light. A misfire occurs when one or more cylinders in the engine fail to ignite the fuel mixture at the right time. This can cause the engine to run rough, hesitate, or stall. If left unchecked, it can also cause damage to the catalytic converter and other engine components. 

Moreover, you will also observe that when you are driving at high speeds, the RPM will fluctuate a lot.

 The misfire can be detected by the Powertrain Control Module (PCM), which will then trigger the check engine light and store a P0300 engine misfire code.

The P0300 engine misfire code is a generic code that indicates that there is a problem with one or more cylinders misfiring.

The PCM uses various sensors to determine which cylinder is misfiring and will store a specific code for that cylinder as well. The P0300 code is often accompanied by other codes, such as P0301, P0302, P0303, or P0304, which indicate which cylinder is misfiring.

If you don’t have idea about engine cylinder numbers, you can read this guide.

Other Causes That Can Result In Car Starting and Stalling Issues

If you checked the ignition control module and distributor, but couldn’t fix the issue, I would highly recommend you check fuel injectors, fuel pump, spark plug cables, vacuum leaks, EGR valve, knock sensor, fuel filter and cam phaser. In addition, you should check the ground connections of the ECM.

Furthermore, connections on engine’s computer are very sensitive, meaning that even a small wiring issue can cause a significant problem. One person was facing vehicle no starting issues that had 350 TBI engine. He found that harness that connected to the distributor had been removed from the retainer, which likely caused some electrical signals to be lost or disrupted. This caused the car to not run or idle as it should have.

The person reconnected (tightened) the connector pins that were connected to the ignition module. They then placed the harness back into the retainer, which secured it in place and allowed all electrical signals to flow as they should have.

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