Engine Will Not Start – But, Fuel Pump, Spark And Compression Are Good

Engine Will Not Start - But, Fuel Pump, Spark And Compression Are Good
Engine Will Not Start - But, Fuel Pump, Spark And Compression Are Good

All engines require three things to start and run; spark, fuel and compression.

So, if any one of these is missing, your engine will not start.

With a engine will not start issue, the possible causes are plenty; so it’s important to understand, what it takes to make a engine start and run.

Your engine will not start, is an all too familiar experience, for any vehicle owner.

Basic Checks For Engine Will Not Start Are:

  • Check the Security System
  • Test Fuses
  • Check for Spark
  • Do you have Fuel
  • Check Engine Trouble Codes
  • Crankshaft Angle Sensor
  • Check for Injector Pulse
  • Check Cylinder Compression

So, like most people you checked the most important things first:

  • The fuel pump is running and delivering normal pressure to the engine
  • The engine has spark
  • There is good compression

But, with all that working your engine still will not start.

So, the most likely cause, is that the fuel injectors are probably not opening.

Engine Will Not Start
Fuel Injectors Are Probably Not Opening

The (PCM) uses the trigger signal from the crankshaft position sensor; and/or camshaft position sensor to pulse the injectors.

So, a worn-out belt can prevent the Crankshaft-Camshaft Position Sensor from synchronizing; causing the sensor to send the wrong signal. When you turn on the key, the injectors should receive battery voltage.

Also, the (PCM) driver circuit provides the ground connection, to energize the injectors. In extreme cases the (PCM) may have failed. In some cases, a (PCM) problem, will cause the vehicle, not to run at all. The (PCM)’s functions include; positioning the crankshaft and controlling the ignition spark and timing. So, if there are problems with how the (PCM) performs these functions, the vehicle may not run.

First, check for voltage at the injectors, when the key is turned on.

  • No voltage?

The problem could be:

  • Blown injector circuit fuse
  • Bad fuel injector power relay
  • A fault in the wiring harness to the injectors

So, the injector fuse and relay are usually located; in the relay box or power distribution center in the engine compartment. Fuses are used to protect various electrical circuits, while supplying power to components. They help the fuel pump, fuel injection and computer systems; from suffering a short circuit. When these fuses blow the system they support stops working and the engine stops running. As a result, the engine will not start. Due to how important the circuits are, it’s so crucial that they can be fixed if they break. Luckily, lots of companies are now using easier technology to make sure car owners can fix this themselves. For example, Selector switches simplify assembly, so people should be able to control the circuit more effectively. By using switches, people can break or change the circuit, allowing them to try and fix the problem and start the car again.

Consequently, there are two methods of checking electrical fuses that protect various components.

You can either pull each fuse out and inspect it or use a test light to check its continuity. If there is a blown fuse check the system it controls. Once the system is identified; inspect or replace the failed part and retry the engine. If the fuse still blows; you will need to check the wiring harness for damage and repair it.

Checking Fuses And Voltage
Checking Fuses And Voltage

If the fuse is okay, try swapping the relay with another; to see if that gets voltage to the injectors.

  • No change?

Try Swapping Relays
Try Swapping Relays

Typically, when injectors fail, the solenoids often short internally, causing a drop in resistance. If the specification calls for 3 ohms and an injector measures only 1 ohm; it will pull more current. Too much current flow to an injector; may cause the (PCM) injector driver circuit to shut down. As a result, killing any other injectors that also share that same driver circuit.

TIP: Try unplugging the injectors; one at a time and crank the engine to see if it will start. If the engine starts when a particular injector has been unplugged; that’s the shorted injector that needs to be replaced.


TIP: You can also measure the resistance of each injector with an ohmmeter. Unplug the injector and measure the resistance, between the two terminals. If resistance is outside specifications (high or low), replace the injector.

Noid Light kit
Noid Light kit

Professional technicians use a tool called a NOID light to check injector pulses. The tool detects digital signals in a circuit and flashes an LED light. No flashes from the injector circuit when cranking the engine; would tell you the (PCM) is not pulsing the injectors. On newer gasoline direct injection (GDI) systems, however, a NOID light is no help.

If the injectors appear to be working, but the engine will not start; the engine may be flooded. As a result, you may have to remove the spark plugs to let them dry. Wait awhile, then try it again.

Conclusion

You can also try, holding the gas pedal all the way down when cranking. Finally, this will put the (PCM) into the “Clear Flood” mode, when cranking the engine.

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