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Troubleshooting
/ Cranks
but Wont Start
Engine Cranks But Will Not Start
Troubleshooting Procedure
(Definition: the key is turned and the engine cranks, but does not start)
For an
engine
to run, you need three things to happen inside the engine.
Compression,
fuel and
ignition, without any one of these components the engine will not run.
Compression: All
internal
combustion engines require
compression to run. The most popular reason for an engine to lose compression
is a timing belt or timing chain fails. Remove the spark plugs and perform a compression
test. Most engine's normal compression reading is between 125 psi. and 160 psi.
on each cylinder.
Fuel: All internal combustion engines require fuel pressure to operate.
One of the most popular reasons for a fuel system to fail is the fuel pump. This
cause's the fuel pressure to drop and engine to stall or not start at all. To check
the fuel pump pressure, remove the fuel rail pressure inspection port and attach
a fuel pressure gauge. Fuel pressure reading's vary depending on the system your
in our vehicle, but most throttle body injection cars (TBI) are between 13 psi and
17 psi. and most (DPI) direct port inject systems are between 40 psi and 55 psi.
Spark: An electric spark is used to ignite the fuel air mixture in the combustion
chamber. This spark is generated by the
ignition system by the use of an ignition coil. Once the spark has been generated
it is transferred to the spark plug for fuel ignition. Some of the most popular
reasons for spark operation failure is ignition coil, ignition distributor, ignition
module and crank angle sensor or spark plug.
Basic Checks:
A. Test Fuses. Test both under hood
power
distribution center and the
fuse
panel under dash. This is done 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.
B. Testing Fuel Pressure
Test for proper fuel pressure with a test gauge on the fuel rail, most throttle
body injection cars (TBI) are between 13 psi and 17 psi. and most (DPI) direct port
inject systems are between 40 psi and 55 psi. If no or little fuel pressure is observed
and there is 12 volt power present the fuel pump, the fuel pump needs replacing.
C. Checking Timing
Belt Test for compression by removing a spark plug and insert a compression
gauge. Crank the engine over about 5 seconds the gauge should read between 125 psi
and 165 psi, if no compression is observed remove front engine cover to inspect
timing belt or chain. Crank engine to observe cam rotation, if the cam does not
rotate the timing belt or chain has failed. (note: if the timing belt drives the
water pump it is best to replace the water pump at this time)
D. Test for Injector Pulse
Remove injector connector to insert injector test light (node) or volt meter.
Observe light flash or gauge pulse while cranking. If light/voltmeter doesn't
respond,
an ignition distributor/crank angle sensor (CKS) or an ignition module is most likely
your problem.
E. Test for Ignition Spark Remove spark plug wire, insert an extra spark plug into end of wire,
rest
spark plug next to a ground source then crank engine. You should observe a blue spark between
the spark plug gap and ground source. If no spark is observed, an ignition coil, ignition rotor or spark
plug wires might have failed. (always keep hands away from engine when
cranking)
Troubleshooting
/
Cranks
but Wont Start
Check Manufacturer Specific Engine
Wont Start Questions and Answers
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