Step 1 -
Anytime you have a problem with electronically
controlled components such as an engine, transmission, ABS brake, or SRS (supplemental
restraint system, Air Bag) inspect all
using a test light and
check the under hood power distribution center and under dash fuse panels. If
all fuses test okay continue to the next step.
Step 2 -
To check for problems with electronically controlled
components such as an engine, transmission, ABS brake, or SRS (supplemental
restraint system, Air Bag) and the fuses test okay a trouble code scan is needed
to identify any system trouble. Use a simple
to retrieve trouble codes
and see if they relate to the specific problem, like a
crank angle sensor
failure code. If the trouble code present does not pertain to the immediate
problem like an EVAP code ignore it until a later time, after the car is running.
The reason we repair non-related codes after the engine is running is because
sometime false codes can be triggered by the engine not running. Once the engine
is running again the code present might cycle and turn itself off. You might
say "if the engine doesn't run shouldn't it have a trouble code?" Sometimes
conditions occur that will not be detected by the computer, example: if the
fails the computer cannot
detect the failure, so the engine doesn't start and the computer thinks everything
is okay with no codes. If no trouble codes are present proceed to the next step.Step 3 -
in your engine are used to ignite the compressed fuel air mixture. If
the condition of the spark plugs are fouled by excessive fuel or carbon the engine
will not start, backfire or run rough. Remove all spark plugs to inspect their condition.
Please use this spark plug condition reference guide to see how the spark plugs
Step 4 -
Determine if the engine has
, this can be
done a number of ways but the most complete method is to perform a compression check.
Remove the spark plugs and perform a compression test on one cylinder. If one cylinder
has compression then the remaining cylinders usually will be close to the same.
Crank the engine over about 5 seconds, normal compression readings should be between
125 psi and 160 psi on each cylinder. If no or little compression exists additional
tests will be needed. The most common reason for an engine to lose compression is
a timing belt
or timing chain failure.
If low or no compression exists remove the oil fill cap and observe
when the engine is cranked over. If no rotation exists the timing belt or chain
has failed. If your engine has a timing belt and you cannot see the camshaft easily
remove the upper bolts to the timing cover and gain visual access to the belt, recheck
cam rotation by cranking the engine over. Sometimes a timing belt or chain can jump
causing the camshaft to lose correlation with the crankshaft and therefore causing
low compression. The best test for this condition is to remove the timing belt/chain
cover and inspect timing marks. If the compression is ok proceed to next step.
Step 5 -
ignition system output
systems can vary in configuration but operate on the same principal. Ignition systems
can consist of a coil, pick up coil, crank angle sensor, cam angle sensor, spark
plugs, spark plug wires, distributor cap, ignition rotor and a distributor and any
variations of these components. An ignition coil is a voltage stepper coil that
transforms a low voltage (12 volts) signal into tens of thousands of volts needed
to jump the gap of the spark plug.
This coil is activated by an ignition module triggered by using the camshaft/crankshaft
angle sensor; timing is adjusted by the PCM (computer).This primary electrical signal
is generated by the PCM which calculates spark timing by using a variety of sensors
including coolant temperature
mass air flow
and oxygen sensors
. To perform
a basic ignition output test you must have a
the ignition system output test video.
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
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
, 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 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.
(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
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
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
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
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
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
becomes slightly plugged will melt the sensor causing the system to
shut down. Inspect sensor for melting at the
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.