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.

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

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 will not start.

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

Engine Will Not Start
Engine Will Not Start

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

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.

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

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. 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.

Voltage
Voltage

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

  • No change?

Engine Will Not Start
Engine Will Not Start

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 cranking 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. You may have to remove the spark plugs to let them dry. Wait awhile then try it again.

Note;

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

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