Troubleshooting Guide: Spark And Fuel Pressure Won't Start

If your car has fuel and spark but still won't start, there are a few potential issues that could be causing this problem. Firstly, check if the engine is getting fuel by using a fuel pressure gauge to measure the fuel pressure. If there is no fuel pressure, this could indicate a faulty fuel pump or a fuel pump circuit issue. Another potential issue could be with the injector pulse, which is the signal from the computer to the injectors telling them when to open and allow fuel into the engine. If there is no injector pulse, check for power going to the injectors and the computer's ground signal to the injectors. Additionally, make sure to check the ignition system and compression. If the ignition system is not delivering a strong spark, there could be an issue with the ignition coil or the engine speed sensor. Checking the engine compression can also help identify any base engine mechanical issues.

Check the engine's fuel supply

If your engine cranks but won't start, there could be a problem with the engine's fuel supply. Here are some steps to check and troubleshoot the issue:

Check the Fuel System:

First, check the fuel pressure up to the fuel rail. This can be done using a fuel pressure gauge. Simply hook it up to the fuel rail, turn the key on or crank it over, and take a reading. Most older vehicles have a fuel pressure test port, allowing you to screw the gauge onto the fuel rail easily. If your vehicle doesn't have a test port, you can tap into the fuel pressure line going to the throttle body or fuel rail to take a reading. Newer vehicles use a fuel rail pressure sensor, which sends a digital signal to the computer. If there is no fuel pressure, this could indicate a faulty fuel pump or a fuel pump circuit issue.

Inspect the Injector Pulse:

The injector pulse is the signal from the computer to the injectors, telling them when to open and allow fuel into the engine. To test this, use a tool called a noid light. Plug the noid light into the injector connector after disconnecting it from the fuel injector. It should blink if it has power and a ground signal trigger from the computer. If there is no injector pulse, check for power going to the injectors and, if necessary, the computer's ground signal to the injectors. The computer uses inputs like the throttle position sensor, engine speed sensor, and coolant temp sensor to determine the injector pulse.

Verify Fuel Delivery:

Another test you can perform is to check if the engine runs on starting fluid. Spray starting fluid into the intake or induction system while someone cranks the engine. If it runs, you know the ignition system, compression, and timing are working correctly, and the issue is related to fuel delivery.

Check Compression:

Low or no compression could be caused by base engine mechanical issues. Check the engine compression by removing the front timing cover and inspecting the timing marks or valve cover for any visual damage. You can also use a compression gauge, screwing it into the spark plug hole after removing the spark plug, and then cranking the engine to take a reading. Ensure that the compression is relatively the same in all cylinders.

Check for fuel pressure

Checking for fuel pressure is a crucial step in diagnosing car issues, especially when you're experiencing problems with starting your vehicle. Here's a detailed guide on how to check for fuel pressure:

Step 1: Safety First

Working with fuel systems can be dangerous, so it's important to take the necessary safety precautions. Always wear protective gear, such as safety glasses and gloves, to safeguard yourself from any potential hazards. Ensure you're working in a well-ventilated area, as fuel vapors are highly flammable. Avoid any activities that could create sparks, such as smoking, and have a fire extinguisher nearby as a precaution.

Step 2: Check the Fuel Pressure

Start by idling your car. Install a fuel pressure tester or gauge, which you can usually attach to the fuel rail or the fuel pump test fitting. This tester will help you determine the fuel pressure in your system. Compare the pressure reading you get with the manufacturer's specifications for your vehicle. If the pressure is lower than specified, you may need to address issues with the fuel pump or fuel filter.

Step 3: Perform a Fuel Volume Test

If the fuel pump is supplying sufficient pressure, the next step is to ensure that the proper amount of fuel is being delivered to the fuel injectors. For this, you can use a flowmeter, if you have access to one, or perform a timed fuel delivery test. Collect a fuel sample for a specified duration (e.g., five seconds) with the pump running, and compare the amount of fuel collected with the manufacturer's specifications.

Step 4: Understanding Fuel Pressure Readings

Zero fuel pressure usually indicates a dead fuel pump or a pump that is not receiving power. In this case, check the fuel pump fuse, and if necessary, replace it. Low fuel pressure can be caused by a clogged fuel filter or a failing fuel pump. If you suspect a clogged filter, consider replacing it, as this is a relatively inexpensive fix. High fuel pressure can be due to a clogged or kinked fuel return line, a faulty fuel pump driver module, or a faulty fuel pressure regulator.

Step 5: Additional Checks

Before investing in a fuel pressure tester, there are some preliminary checks you can perform. First, ensure that your gas tank actually has fuel in it, as fuel gauges can sometimes be faulty. If the tank appears full but the car still won't start, consider checking the fuel gauge for internal failure. Additionally, listen for the fuel pump to pressurize the fuel line when the ignition switch is turned on. If you don't hear any noise, it could indicate an issue with the pump not receiving power or a faulty pump.

Check the ignition system

If your car has spark and fuel pressure but still won't start, you should check the ignition system.

On a standard ignition system, the secondary ignition components should deliver a strong, bright blue spark that can jump at least half an inch of a gap while cranking the engine. Depending on your setup, you could have ignition wires that send the ignition to each cylinder, or you could have "coil over plug". Either way, access the wire or coil and insert a spark tester or screwdriver in place, grounding the other end. Watch for a bright blue spark while an assistant cranks the engine.

There is also the primary ignition system. This is the engine speed sensor or sensors (cam or crank sensor). Some vehicles use just the crank sensor, while others use both the cam and the crank sensor to produce a spark. On some more complex vehicles and engines, there might be two or more camshaft position sensors that can affect the spark. Both the primary and secondary ignition systems can fail (and even intermittently) causing a no-spark condition. If there is no spark while cranking, be sure to check for power to the ignition coil or coils with the key on and while cranking the engine.

Check for injector pulse

If your car has spark and fuel pressure but won't start, one of the potential issues could be with the fuel injectors. Here are some detailed steps to check for injector pulse:

Checking Injector Pulse:

Using a Mechanic's Stethoscope:

• Start by starting the engine and letting it idle.
• Apply the parking brake and open the hood of the car.
• Place the earpiece of a mechanic's stethoscope on your ears.
• Place the tip of the stethoscope against the side of the injector. Alternatively, you can use a long standard screwdriver or a piece of thin hose of appropriate length.
• Listen for a clicking sound as the injector's valve opens and closes. This sound indicates that the injector is receiving a pulse signal from the computer.
• Repeat this test for each injector and make note of any that are not producing a clicking sound, as they may need further testing or replacement.

Using a Test Light:

• First, hook the test light clip to a bolt or bare metal bracket on the engine.
• Unplug the electrical connector from the fuel injector you want to test.
• Turn the ignition switch to the 'ON' position.
• Touch the terminals of the harness connector one at a time with the test light. One of the terminals should illuminate the test light, indicating the injector power source from the computer.
• Now, plug the harness connector back into the fuel injector and hook the test light clip to the positive side of the battery.
• Have an assistant crank or start the engine.
• Back probe the opposite wire on the fuel injector connector, which is the pulse signal coming from the computer. The test light should flash, indicating that the injector is receiving the pulse signal.

Using a Voltmeter:

• Remove the fuel pump fuse to prevent the car from starting during the test.
• Unplug the injector in question and insert the positive voltmeter lead into one of the two connector slots from the injector wiring harness.
• Touch the other lead to the engine metal (not plastic) for a ground connection.
• Have an assistant turn the key on. Test the second connector slot if there is no voltage.
• Normally, you should see a battery voltage of around 12.6 volts. If there is no voltage, the voltage supply circuit may need repair.
• Test the injector circuit for ground. If there is voltage present, insert the ground voltmeter lead into the open slot of the connector.
• With the engine cranking, the voltage reading should fluctuate as the ground signal is applied and then removed. If using a digital meter, the reading may be challenging to determine due to the meter's slow response. However, the fluctuating voltage indicates a normal circuit.
• If there is no ground signal, the issue likely lies with the computer or related wiring.

Check for engine compression

If your car has spark and fuel pressure but still won't start, it's worth checking for engine compression. Engine compression is one of the four major variables that determine how smoothly your engine runs. The others are the fuel/air mixture, spark (in a gas engine), and timing.

Compression refers to the ability of the engine's pistons and valves to compress the ingested air and fuel. In a diesel engine, this compression causes the fuel to ignite on its own. In a gas engine, the mixture is ignited by a spark plug.

A compression test is one of the most basic engine diagnostic procedures and can help you understand what your engine is doing and where the problem may lie.

How to Perform a Compression Test

Warm Up the Engine

Bring the engine to its normal running temperature. If the engine is cold, start the vehicle and keep it running for 5 to 10 minutes. Be careful not to overheat the engine. If you've recently taken your car for a long drive, give it at least 30 minutes to cool down.

Prepare for the Test

Put on insulated gloves and safety glasses for protection. If the engine is hot, wear heat-resistant gloves to protect yourself from burns. Safety glasses will protect your eyes from possible gas and oil spray when you're detaching engine components.

Disable the Ignition and Fuel Systems

Make sure the engine is switched off and remove the key from the ignition. Locate the fuse box, which is usually inside the engine compartment, and remove the fuel pump or injection fuse. This will prevent gas from flowing to the engine during the test.

Next, disconnect the ignition coil fuse in the fuse box or, if your vehicle doesn't have one, locate the ignition coil in the engine compartment and pull off the big wire plugged into the top part of the coil.

Detach Spark Plug Wires and Remove Spark Plugs

Check the engine for a series of black cables coming out of the top end. Grasp each wire at the end and twist it while pulling it up to detach it from the engine block. Label the wires so you know which spark plug each one connects to.

Now, remove the spark plugs with a socket wrench. Fit the wrench with an extension handle and a spark plug socket, and turn the spark plug counterclockwise until you can lift it out of the engine. Label each spark plug and lay them out in a secure spot.

Perform the Compression Test

Locate the first cylinder, which is usually the one closest to the front of the engine. Put the compression test adapter into the cylinder and connect the compression gauge to the other end of the hose. Crank the engine at least four times and check the compression gauge for the result.

Repeat this process for all the other cylinders, recording each result.

Interpreting the Results

For a standard engine, the pressure readouts should be between 125 and 175 PSI. For diesel engines, the optimal PSI is between 275 and 400.

If there is a significant difference between the highest and lowest cylinder ratings, it indicates engine problems. Individual cylinders with low readings could indicate cylinder-specific issues like worn-out piston rings.

If two adjacent cylinders have low ratings, it could be a sign of a blown head gasket between them. Milky oil or cloudy exhaust fumes can also indicate a blown head gasket.

If all the cylinders have low readings, it could be a sign of a valve timing issue. Verify that the valves are opening and closing correctly and that the timing belt or chain is intact.

Diagnosing and Fixing the Problem

A lack of compression is usually caused by worn or damaged piston rings, damaged valves, improper valve timing, or a blown head gasket.

If individual cylinders have low PSI, you can try adding a teaspoon of fresh engine oil directly into the open cylinder and retesting. If the PSI increases, it's likely that the piston rings are worn out.

If two adjacent cylinders have low PSI, there may be a blown head gasket between them.

If all cylinders have low PSI, check the valve timing and ensure the valves are opening and closing properly. If the valves are functioning correctly, try the oil test described above. If the PSI increases, your engine may need a rebuild due to significant ring wear.

Remember, low compression in any cylinder is a major concern and should be addressed immediately to avoid further problems.

Frequently asked questions