Engine Cranks But Wont Start
If the ignition system test is weak or non-existent test the car fuses, both
under hood power distribution center and the fuse panel under dash. This test is
performed with a test
light tool. The test light should illuminate on both sides of the fuse, if not
the fuse has failed and needs to be replaced. If the fuses are ok a manufacturer
specific repair procedure is required and an online auto repair manual is needed
to continue. If the ignition system tests ok proceed to the next step.
Step 6 -
Test fuel system
pressure, test for proper fuel pressure with a test gauge on the fuel rail or
in line somewhere in the system, most throttle body injection cars (TBI) are between
13 psi and 17 psi. Most (DPI) direct port inject systems are between 40 psi and
55 psi. If good fuel pressure is present continue to next step. If no or little
fuel pressure is present check the
fuel pump fuse and
fuel pump control relay located in the fuse panel, you can find this fuse and relay
by checking your owner's manual, back of the fuse panel cover diagram, or an online
auto repair manual, if the fuse or relay has failed replace it a new unit and re-test.
Checking Fuel System Pressure Video
(Note: some Ford cars have an inertia switch designed to cut off the fuel pump in the event of an accident. Sometimes this switch can accidentally be triggered causing the engine to not start. If the car is exposed to a random bump either in the road or by another car this switch can be triggered. To check for this condition locate the inertia switch, if the cut off switch has been active it will have a white or red indicator at the top of the switch. Push this indicator down to disarm the cut off switch, if the indicator does not move down it is not activated and is not the problem.) Have a helper crank over the engine while you place your fingers over the relay, does the relay click under your fingers? If so the relay could be working, there is a chance the relay has burned contacts inside causing the problem but we will get back to that. Next, access the fuel pump power feed wire, there are a few ways to do this, first you need a wiring schematic to find the color wire needed for testing, the best way to do this is with an online auto repair manual. Once you have found the color wire it should be located in the wiring harness near the fuel tank were the pump is located. Ground the test light and probe (pierce the wire's outer coating with the test light point) the wire, have a helper crank the engine over. If the test light illuminates and you have no fuel pressure the fuel pump had failed and needs to be replaced. If the test light doesn't illuminate the fuel pump control relay has probably failed, replace it with a new unit and re-test, in most cases this relay is under thirty dollars. There is an outside chance the power feed to the relay has failed but it doesn't happen very often. If this is the case use an auto repair manual to trace the power source to the relay. Step 7 - Test fuel injector pulse and supply voltage output (test is used for most cars). This test will tell you if the computer system has operating voltage and injector trigger signal. Remove an electrical connector from a fuel injector (it doesn't matter which injector) probe both sides of the connector with a grounded test light (there are only two terminals). Have a helper turn the key to the "on" position without cranking the engine and observe the test light. The test light should illuminate one side of the connector only. Next, switch the test light lead to the positive side of the battery to test the system ground injector trigger, probe the side of the connector that did not light up, have a helper crank the engine over and observe the test light, it should blink on and off. If this test checks ok continue to next step. (Note: if no injector pulse is present try disconnecting the remainder of injectors and re-test, if a fuel injector is shorted it can shut down the injector driver causing no injector pulse. If injector pulse returns plug injectors electrical connectors in one at a time until the pulse fails and replace that injector) If this test revealed that there was no pulse but system has power the PCM is not generating a fuel injector trigger. If there is no trigger to the fuel injector it will not allow fuel to enter into the engine. Some of the most popular reasons that can cause this condition include a shorted crankshaft angle sensor, shorted camshaft position sensor or shorted PCM. (When a system trouble code scan is performed it does not always catch a crankshaft angle sensor, camshaft position sensor failure).
Tip: try disconnecting all non-essential sensors, example: oxygen sensor, coolant sensor, throttle position sensor, air intake temperature sensor, mass air flow or map sensor and EGR valve pressure differential sensor. Crank the engine over, if the injector pulse returns, one of the sensors is shorted causing the system to not operate. Plug the sensors in one at a time until the injector pulse fails then replace that sensor and reassemble. (Note: Some Ford cars have an EGR valve pressure differential sensor that when the catalytic converter becomes slightly plugged will melt the sensor causing the system to shut down. Inspect sensor for melting at the electrical connector then repair or replace as needed and recheck). If the test reveals that the connector has no power on either side at any time the system power has been disrupted. Some of the most common reasons for this is condition are the main PCM fuse, main PCM power relay and main PCM power feed wire failure. (Some vehicle PCM feed wires are located near the battery and corrosion can stop the voltage feed). If all power sources check out the system ground needs to be checked, this is done by reversing the test light lead and installing it on the positive side of the battery. Now the test light will illuminate when grounded. Use the test light to check main system grounds to the PCM, most system ground wires are black but to be sure you will need an online auto repair manual. If repairs have recently been made a system ground lead could have been left off of the engine causing the system not to power up, so double check all engine wiring harness grounds. Step 8 - If the engine has compression, ignition and fuel injector pulse and the engine still doesn't run it could have a plugged exhaust system. Disconnect the exhaust system before the catalytic converter and crank over, if the engine starts the car has a plugged converter or exhaust system. Disassemble the exhaust system to inspect to replace the exhaust component that has failed and reassemble to recheck. If further assistance is needed, our certified car repair technicians are ready to answer your car questions.
Related Car Repair Information
Checking Fuel System Pressure Video
(Note: some Ford cars have an inertia switch designed to cut off the fuel pump in the event of an accident. Sometimes this switch can accidentally be triggered causing the engine to not start. If the car is exposed to a random bump either in the road or by another car this switch can be triggered. To check for this condition locate the inertia switch, if the cut off switch has been active it will have a white or red indicator at the top of the switch. Push this indicator down to disarm the cut off switch, if the indicator does not move down it is not activated and is not the problem.) Have a helper crank over the engine while you place your fingers over the relay, does the relay click under your fingers? If so the relay could be working, there is a chance the relay has burned contacts inside causing the problem but we will get back to that. Next, access the fuel pump power feed wire, there are a few ways to do this, first you need a wiring schematic to find the color wire needed for testing, the best way to do this is with an online auto repair manual. Once you have found the color wire it should be located in the wiring harness near the fuel tank were the pump is located. Ground the test light and probe (pierce the wire's outer coating with the test light point) the wire, have a helper crank the engine over. If the test light illuminates and you have no fuel pressure the fuel pump had failed and needs to be replaced. If the test light doesn't illuminate the fuel pump control relay has probably failed, replace it with a new unit and re-test, in most cases this relay is under thirty dollars. There is an outside chance the power feed to the relay has failed but it doesn't happen very often. If this is the case use an auto repair manual to trace the power source to the relay. Step 7 - Test fuel injector pulse and supply voltage output (test is used for most cars). This test will tell you if the computer system has operating voltage and injector trigger signal. Remove an electrical connector from a fuel injector (it doesn't matter which injector) probe both sides of the connector with a grounded test light (there are only two terminals). Have a helper turn the key to the "on" position without cranking the engine and observe the test light. The test light should illuminate one side of the connector only. Next, switch the test light lead to the positive side of the battery to test the system ground injector trigger, probe the side of the connector that did not light up, have a helper crank the engine over and observe the test light, it should blink on and off. If this test checks ok continue to next step. (Note: if no injector pulse is present try disconnecting the remainder of injectors and re-test, if a fuel injector is shorted it can shut down the injector driver causing no injector pulse. If injector pulse returns plug injectors electrical connectors in one at a time until the pulse fails and replace that injector) If this test revealed that there was no pulse but system has power the PCM is not generating a fuel injector trigger. If there is no trigger to the fuel injector it will not allow fuel to enter into the engine. Some of the most popular reasons that can cause this condition include a shorted crankshaft angle sensor, shorted camshaft position sensor or shorted PCM. (When a system trouble code scan is performed it does not always catch a crankshaft angle sensor, camshaft position sensor failure).
Tip: try disconnecting all non-essential sensors, example: oxygen sensor, coolant sensor, throttle position sensor, air intake temperature sensor, mass air flow or map sensor and EGR valve pressure differential sensor. Crank the engine over, if the injector pulse returns, one of the sensors is shorted causing the system to not operate. Plug the sensors in one at a time until the injector pulse fails then replace that sensor and reassemble. (Note: Some Ford cars have an EGR valve pressure differential sensor that when the catalytic converter becomes slightly plugged will melt the sensor causing the system to shut down. Inspect sensor for melting at the electrical connector then repair or replace as needed and recheck). If the test reveals that the connector has no power on either side at any time the system power has been disrupted. Some of the most common reasons for this is condition are the main PCM fuse, main PCM power relay and main PCM power feed wire failure. (Some vehicle PCM feed wires are located near the battery and corrosion can stop the voltage feed). If all power sources check out the system ground needs to be checked, this is done by reversing the test light lead and installing it on the positive side of the battery. Now the test light will illuminate when grounded. Use the test light to check main system grounds to the PCM, most system ground wires are black but to be sure you will need an online auto repair manual. If repairs have recently been made a system ground lead could have been left off of the engine causing the system not to power up, so double check all engine wiring harness grounds. Step 8 - If the engine has compression, ignition and fuel injector pulse and the engine still doesn't run it could have a plugged exhaust system. Disconnect the exhaust system before the catalytic converter and crank over, if the engine starts the car has a plugged converter or exhaust system. Disassemble the exhaust system to inspect to replace the exhaust component that has failed and reassemble to recheck. If further assistance is needed, our certified car repair technicians are ready to answer your car questions.
Related Car Repair Information