How to Diagnose No Spark or Loss of Power on a Modern Car
Content
Misfires caused by loss of power in a vehicle are difficult to diagnose but must be corrected to avoid further damage and costly repairs.
Misfires are a common vehicle handling problem that can take some time to diagnose, depending on the cause. When an engine misfires, one or more cylinders are not working properly, either due to ignition problems or fuel problems. Engine misfires are accompanied by a loss of power that is directly proportional to the severity of the misfires.
When idling, the engine can shake so hard that the vibration is felt throughout the car. The engine may run poorly and one or more cylinders may be misfiring. The check engine light may come on or keep flashing.
The most common cause of misfiring is a problem with the ignition system. Misfiring can be caused by a loss of spark; unbalanced air-fuel mixture; or loss of compression.
This article focuses on finding the source of a misfire caused by a loss of spark. The loss of spark is caused by something that prevents the coil from jumping across the electrode gap at the end of the spark plug. This includes worn, dirty, or damaged spark plugs, faulty spark plug wires, or a cracked distributor cap.
Sometimes misfires can be caused not by a complete loss of spark, but by improper sparking or high voltage leaks.
Part 1 of 4: Find the Misfire Cylinder(s)
Necessary materials
- Scan Tool
Step 1: Scan the car to find cylinder misfires.. Use a scan tool to find the Diagnostic Trouble Code (DTC) numbers for the problem.
If you don't have access to a scan tool, your local parts store can scan your car for free.
Step 2: Get a printout with all code numbers. The DTC numbers indicate the specific circumstances in which the collected data does not match the allowed values.
Misfire codes are universal and go from P0300 to P03xx. "P" refers to transmission and 030x refers to detected misfires. "X" refers to the cylinder that misfired. For example: P0300 refers to random misfire, P0304 refers to cylinder 4 misfire, and P0301 refers to cylinder 1, and so on.
Pay attention to all ignition coil primary circuit codes. There may be other DTCs, such as coil codes or fuel pressure codes related to fuel delivery, spark, or compression, that can help you diagnose the problem.
Step 3: Determine the cylinders on your engine. Depending on the type of engine in your car, you may be able to identify a particular cylinder or cylinders that are not working.
The cylinder is the central part of a reciprocating engine or pump, the space in which the piston moves. Several cylinders are usually arranged side by side in an engine block. In different types of engines, the cylinders are located in different ways.
If you have an inline engine, cylinder number 1 will be closest to the belts. If you have a V-twin engine, look for a diagram of the engine's cylinders. All manufacturers use their own cylinder numbering method, so visit the manufacturer's website for more information.
Part 2 of 4: Checking the coil pack
The coil pack generates the high voltage required by the spark plug to generate the spark that starts the combustion process. Check the coil pack to see if it's causing misfire problems.
Necessary materials
- Dielectric grease
- ohmmeter
- wrench
Step 1: Find the spark plugs. Access the coil pack to test it. Turn off the car engine and open the hood.
Locate the spark plugs and follow the spark plug wires until you find the coil pack. Remove the spark plug wires and tag them so they can be easily reinstalled.
Functions: Depending on the make and model of your vehicle, the coil pack may be located on the side or rear of the engine.
A warning: Always be careful when handling wires and spark plugs.
Unscrew the coil blocks and remove the connector. Inspect the coil pack and case. When a high voltage leak occurs, it burns the surrounding space. A common indicator of this is discoloration.
- Functions: The boot can be replaced separately if there is one. To properly remove the boot from the spark plug, grasp it firmly, twist and pull. If the boot is old, you may need to use some force to unscrew it. Don't use a screwdriver to try and pry it off.
Step 2: Check the spark plugs. Look for traces of carbon in the form of a black line running up and down the porcelain part of the candle. This indicates that the spark is traveling through the spark plug to ground and is the most common cause of intermittent misfiring.
Step 3: Replace the plug. If the spark plug is misfiring, you can replace it. Make sure you use dielectric grease when installing a new spark plug.
Dielectric grease or silicone grease is a waterproof, electrically insulating grease made by mixing silicone oil with a thickener. Dielectric grease is applied to electrical connectors to lubricate and seal the rubber parts of the connector without arcing.
Step 4: Remove the coil pack. Remove the bumper panels and roll bar for easier access. Remove the three Torx head bolts from the coil pack you are about to remove. Pull the bottom high voltage wire out of the coil pack you plan to remove.
Disconnect the coil pack electrical connectors and use a wrench to remove the coil pack from the engine.
Step 5: Check the Coils. Leave the coils unscrewed and barely resting on the fork. Start the engine.
- A warning: Make sure no part of your body touches the car.
Using an insulated tool, lift the spool approximately ¼ inch. Look for arcs and listen for clicks, which may indicate a high voltage leak. Adjust the amount of coil lift to get the loudest sound of the arc, but do not raise it more than ½ inch.
If you see a good spark at the coil but not at the spark plug, then the problem may be caused by either a faulty distributor cap, rotor, carbon tip and/or spring, or spark plug wires.
Look down into the spark plug tube. If you see a spark going to the tube, the boot is defective. If the arc slowdown becomes weaker or disappears, the coil pack is faulty.
Compare all coils and determine which one is faulty, if any.
- Functions: If half of your coils are under the intake manifold and that's where the misfire is, remove the intake, change the spark plugs, take known good coils from an available bank and place them under the intake. Now you can download the test of questionable coils.
Part 3 of 4: Check spark plug wires
Spark plug wires can be tested in the same way as coils.
Step 1: Remove spark plug wire. First remove the wires from the plugs and look for obvious signs of a high voltage leak.
Look for cuts or burn marks on the wire or insulation. Check for carbon deposits on the spark plug. Check the area for corrosion.
- Functions: Visually inspect the spark plug wires with a flashlight.
Step 2: Check the wire. Lower the wire back onto the plug to prepare for stress testing. Start the engine.
Use an insulated tool to remove the wires from the plug one at a time. Now the whole wire and the coil that feeds it are loaded. Use a jumper to ground an insulated screwdriver. Gently run a screwdriver along the length of each spark plug wire, around the coil and boots.
Look for arcs and listen for clicks, which may indicate a high voltage leak. If you see an electric arc from the wire to the screwdriver, the wire is bad.
Part 4 of 4: Distributors
The distributor's job is to do what the name implies, to distribute electrical current to individual cylinders at a predetermined time. The distributor is internally connected to the camshaft, which controls the opening and closing of the cylinder head valves. As the camshaft lobes rotate, the distributor receives power by turning the central rotor, which has a magnetic end that fires individual electrical lobes when it rotates clockwise.
Each electrical tab is attached to a corresponding spark plug wire, which distributes electrical current to each spark plug. The location of each spark plug wire on the distributor cap is directly related to the ignition order of the engine. For example; the standard General Motors V-8 engine has eight individual cylinders. However, each cylinder fires (or reaches top dead center) at a specific time for optimum engine efficiency. The standard firing order for this type of motor is: 1, 8, 4, 3, 6, 5, 7, and 2.
Most modern cars have replaced the distributor and point system with an ECM or an electronic control module that does the similar job of supplying electrical current to each spark plug.
What causes problems with the loss of spark in the distributor?
There are three special components inside the distributor that can cause no spark at the end of the spark plug.
Broken distributor cap Moisture or condensation inside the distributor cap Broken distributor rotor
To diagnose the exact cause of a distributor failure, follow the steps below.
Step 1: Locate the distributor cap. If you have a car made before 2005, it is likely that you have a distributor and therefore a distributor cap. Cars, trucks and SUVs built after 2006 will most likely have an ECM system.
Step 2: Inspect the distributor cap from the outside: Once you've found the distributor cap, the first thing you should do is perform a visual inspection to look for a few specific warning signs, which include:
Loose spark plug wires at the top of the distributor cap Broken spark plug wires at the distributor cap Cracks on the sides of the distributor cap Check for tightness of the distributor cap clamps to the distributor cap Check for water around the distributor cap
Step 3: Mark the position of the distributor cap: Once you have inspected the outside of the distributor cap, the next step is to remove the distributor cap. However, this is where inspection and diagnosis can be tricky and can cause more problems if not done properly. Before you think about removing the distributor cap, make sure you mark the exact position of the cap. The best way to complete this step is to take a silver or red marker and draw a line directly on the edge of the distributor cap and on the distributor itself. This ensures that when you change the cap, it will not be put on backwards.
Step 4: Remove the distributor cap: Once you've marked the cap, you'll want to remove it to inspect the inside of the distributor cap. To remove the cover, you simply remove the clips or screws that currently secure the cover to the distributor.
Step 5: Inspect the Rotor: The rotor is a long piece in the center of the distributor. Remove the rotor by simply sliding it off the contact post. If you notice that there is black powder on the bottom of the rotor, this is a sure sign that the electrode has burned out and needs to be replaced. This could be the cause of the spark problem.
Step 6: Inspect the inside of the distributor cap for condensation: If you checked the distributor rotor and found no problem with this part, condensation or water inside the distributor may be the cause of the spark problem. If you notice condensation inside the distributor cap, you will need to purchase a new cap and rotor.
Step 7: Check the alignment of the distributor: In some cases, the distributor itself will loosen, which will affect the ignition timing. This does not affect the distributor's ability to spark frequently, however it can happen in some cases.
Engine misfiring is usually accompanied by a critical power loss that must be corrected promptly. Determining the cause of a misfire can be difficult, especially if the misfire only occurs under certain conditions.
If you are not comfortable doing this diagnostic yourself, ask a certified AvtoTachki technician to inspect your engine. Our mobile mechanic will come to your home or office to determine the cause of your misfiring engine and provide a detailed inspection report.
