Troubleshooting An Lt1: Fuel Pressure But Won't Start

If your car has fuel pressure but won't start, there are a few things you can check. First, check the spark plugs for fuel and, if they are wet, make sure to dry them. Next, check the injector pulse with a noid light. If there is no pulse, check for power going to the injectors with the key on and while cranking. If there is still no pulse, the problem may lie with a faulty relay, blown fuse, or wiring issue. Additionally, you can try starting the car with the accelerator pedal on the floor before turning the key to start. If the car still won't start, other potential issues could be a faulty fuel pump, a faulty fuel pressure regulator, or a faulty optical sensor.

Check for spark

If your car has fuel pressure but won't start, it's important to check for a spark to help diagnose the issue. Here are some steps you can take to check for a spark and identify potential issues:

Check Spark Plugs and Ignition Coil:

• Pull out one of the spark plugs and inspect it for any signs of damage or wetness. A wet spark plug could indicate that the fuel is not being burned.
• Check for spark by inserting a spark plug tester into the plug boot and grounding it on a clean, unpainted metal part of the engine. Have someone crank the engine and watch for a spark.
• If there is no spark, the issue could be with the ignition coil or the electrical system.
• Locate the ignition coil and check for power using a test light. Check both the positive and negative wires attached to the coil.
• If the positive wire has no power, there may be a break in the wiring between the ignition switch and the coil.
• If the negative wire doesn't light up the test light, there could be a break in the wire between the ignition module and the ignition coil.

Check Distributor and Ignition Module:

• Locate the distributor cap and observe the rotor inside. Have a helper crank the engine while you watch the distributor. If it's not turning, there could be an issue with the timing belt or chain.
• Locate the pulse generator on the distributor and connect an A/C voltmeter to the wires. Crank the engine and observe the current. If there's no current, the pulse generator may have malfunctioned and need replacement.

Additional Checks:

• Check your battery by turning on the headlights. If they're dim or not turning on, you may need to jump-start the car.
• Scan your fuse box for any blown fuses, which can usually be identified by a black or burnt spot.
• Check the fuel injectors with a noid light to ensure they're working properly.
• Check the throttle position sensor (TPS) and ensure it's functioning correctly.
• Check the vacuum line for the fuel pressure regulator for any signs of wet fuel.
• Try starting the car with the accelerator pedal on the floor before turning the key.

Check for fuel

If your car won't start, there are a few quick tests you can run to check if you have enough fuel.

First, check the fuel pump fuse. Often, it's not the pump itself that's the issue, but the power that supplies it. Check your owner's manual for the location of the fuse box, then find the fuse that corresponds to the fuel pump. Pull it out and inspect it for signs of failure. If the fuse is blown, it will be broken or burned. If it looks good, check the rest of the fuses related to the fuel system and replace them if necessary. If no fuses are blown, ask an assistant to turn the key while you listen for the fuel pump relay clicking on.

Next, check the voltage at the pump itself. Just because there is power from the circuit doesn't mean that it's getting to the pump, so it's important to check the voltage there too. You can find out where to check and the proper procedure for checking it in your vehicle's service manual. Test for source voltage to determine whether the charge leaving the fuse is getting to the pump. If no power is making it to the fuel pump, then check the fuel pump relay circuit—you could have a bad relay.

You can also perform a drop test using a voltmeter. Check to make sure that the power wire shows the full voltage and the grounding wire shows that it's grounded properly. If this electrical test doesn't reveal anything, it's likely that your fuel pump is the problem and it will need to be replaced. However, you can check more thoroughly by completing a fuel pressure test.

To perform a fuel pressure test, you'll need to get a fuel pressure gauge. These are commonly available at most auto parts stores for $20-30. Hook the pressure gauge to the fuel pump test fitting, which is usually located near the fuel injectors. Different gauges may have slightly different instructions, and the location of the fuel pump varies from vehicle to vehicle, so consult your owner's manual for more specific instructions. Once the gauge is hooked up, have an assistant rev the engine while you check the gauge. The pressure should match the specifications listed in the repair manual and should increase as the engine is revved. If it doesn’t, you need to replace your fuel pump and filter.

Check for compression

Compression is one of the three essential elements for an engine to start, the other two being fuel pressure and spark. Checking for compression can be done by removing the spark plugs and inserting a compression gauge into the spark plug hole. The gauge is then connected to a wrench, which is turned to crank the engine. A reading is then taken from the gauge.

For an LT1 engine, the compression should be around 10.5:1. A rule of thumb is that all cylinders should be within 10% of the highest reading. Therefore, if the highest reading is 180 psi, then all other cylinders should read between 162 and 180 psi.

If you are experiencing low or no compression, this could be caused by a base engine mechanical issue, such as a broken camshaft, timing belt, or chain. To check for this, you can remove the front timing cover and inspect the timing marks, or remove the valve cover to look for any visual damage.

It is important to note that checking compression requires a specialised compression gauge and can be dangerous. Therefore, it is recommended that you consult a qualified mechanic to perform this test if you are unsure.

Check the ignition system

If your car has fuel pressure but still won't start, you may want to check the ignition system. The ignition system is comprised of the secondary and primary ignition systems. The secondary ignition system includes the spark plugs, ignition wires, distributor cap, and rotor. The primary ignition system includes the engine speed sensor or sensors (cam or crank sensor).

To check the secondary ignition system, access the wire or coil and insert a spark tester or screwdriver in place, grounding the other end. You should watch for a bright blue spark while someone cranks the engine. Check more than one cylinder to be sure the ignition system is working normally.

The primary ignition system can also fail, causing a no-spark condition. If there is no spark while cranking, check for power to the ignition coil or coils with the key on and while cranking the engine over. This could be caused by a blown fuse or relay. Some vehicles or ignition systems use an ignition module as well as the coil or coils, and others are triggered directly from the engine computer but will still need a separate power source for the ignition coil(s) to work.

Check the fuel supply

If your car won't start, there are a few quick tests you can run to check if the fuel supply is causing the problem.

Electrical Test

First, check the fuel pump fuse. Often, it's not the pump itself that's the issue, but the power that supplies it. Check your owner's manual for the location of the fuse box, then find the fuse that corresponds to the fuel pump. If it looks good, check the rest of the fuses related to the fuel system for signs of being blown and replace them if necessary. If no fuses are blown, ask a helper to turn the key while you listen for the fuel pump relay to click on.

Next, check the voltage at the pump itself. Just because the circuit is working doesn't mean the charge is getting to the pump, so it's important to check the voltage there, too. Consult your vehicle's service manual to find out where and how to check it. Test for source voltage to determine whether the good charge leaving the fuse is getting to the pump. If no power is making it to the fuel pump, check the fuel pump relay circuit—you could have a bad relay.

Fuel Pressure Test

If the electrical test reveals nothing, it's likely that your fuel pump is the problem and will need to be replaced. However, you can check more thoroughly by completing a fuel pressure test.

First, eliminate the filter as a possibility. If the filter gets clogged with sediment, you may have trouble accelerating and suspect your fuel pump is at fault. To check it, remove the filter from the vehicle and drain any excess fuel. Use a short piece of rubber hose on the filter inlet, then blow through the filter inlet, paying attention to the resistance, which should be minimal. Inspect the screen for debris and replace the filter if necessary.

Next, get a fuel pressure gauge. These are commonly available at most auto parts stores for $20-30, but you can also often borrow one from machine shops or auto shops. Hook the pressure gauge to the fuel pump test fitting, which is usually near the fuel injectors. Different gauges may have slightly different instructions, and the location of the fuel pump varies from vehicle to vehicle, so consult your owner's manual for specific instructions.

Finally, have a helper rev the engine while you check the gauge. Let the engine warm up slightly, then check the pressure at idle speed and at the rated speed listed in your pump specifications. If you don't know the rated speed, just rev the engine and observe how the pressure reacts. If you have a serious problem, the needle won't move or will drop below specifications, meaning the fuel pump needs to be replaced.

Frequently asked questions