Easy step by step guide on how to repair an automotive engine that has stalled or intermittently stalls while driving, this information is presented in order of popularity and pertains to most vehicles.
Difficulty Scale: 5 of 10
Begin with the vehicle on level ground engine off (cold) with the emergency brake set.
By illuminating the "check engine" warning lamp, the computer has detected a problem which can pertain to engine stalling while driving. Learn more
Step 1 - When a crankshaft angle sensor shorts
out it will cause the engine to stall, this sensor is used to give feedback information
to the engine computer (PCM), this sensor failure is not always picked up by the
computer.
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Step 2 - A fuel pump operation failure will cause
the engine to stall out due to the in-adequate amount of fuel volume and pressure
while the engine is running.
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Step 3 - If injector pulse stops, the engine will
stall. Monitoring the fuel injector pulse can help narrow the problem down, the
following test will need to be modified using longer test wires while locating the
light portion of the test inside the vehicle to be observed while driving.
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Step 4 - If a main system relay or ignition switch
fails the engine will stall intermittently, once the electrical connections cool
down the system will operate again until heated. The computer system uses a steady
supply of voltage to operate, Intermittent stalling can be a frustrating problem
to find, but if a test light is located inside the passenger compartment with the
leads connected to a suspected failed circuit such as the ignition switch. While
observing the light when the engine stalls, either "ON" or "OFF" if the circuit
is okay or faulty, continue testing.
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Step 5 - If a fuse fails the engine will stall,
if the problem is intermittent test the fuses with the engine running and employ
the "wiggle test" which means wiggle all main fuses and relays to see if the engine
stalls then repair the connection. A system fuse is designed to protect an electrical
circuit in case of a short circuit, but when a fuse ages it can become loose causing
an unstable supply of electricity.
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Step 6 - A catalytic converter can effectively
plug the exhaust system causing the engine to stall, this catalytic converter is
designed as part of the vehicle's emission system which can break apart internally.
To check for this condition start with the engine cold, take a rubber mallet and
gently strike the catalytic converter, if it sounds like rocks inside, remove to
inspect for internal damage.
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Step 7 - If the battery cables are loose or corroded
it can cause the engine to stall. Good battery connections are mandatory for the
electrical system to stay healthy and operate correctly.
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Step 8 - When a feedback sensor short circuits
it can cause the computer to shut down, sensors most prone to failure deal with
extreme heat like an oxygen or coolant sensor. There are a variety of sensors that
provide feedback data for the engine management computer PCM (powertrain control
module).
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Step 9 - When the main computer fails, it will cause
the engine to stall. The main computer system or PCM (Powertrain control module)
controls fuel, ignition, transmission and emission systems. (Note: When replacing
a computer re-programming is necessary before installation.)
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Step 10 - If the incorrect weight oil has
been installed the engine will hold open the valves by not allowing the lifters
to bleed down which causes the engine to stall. Engine oil weight is important on
today's close tolerance engines.
Helpful Information A shorted sensor doesn't always set a check engine light or MIL (malfunction
indicator light). The computer is programmed to trigger a "service engine soon light"
when the sensor has failed for a predetermined amount of time, say one minute, it
only takes an intermittent shorting sensor one second to stop the computer system
(stall engine). To troubleshoot this problem, temporally disconnect major sensors
one at a time and retest ie: oxygen, coolant and MAF. (This will cause a service
engine soon light, codes will need to be cleared after testing). When troubleshooting
a stalling problem additional codes maybe present such as an EVAP code which should
be ignored until the more major problems are repaired. Not all electrical problems
can be detected by the computer. Many electronic components are used simultaneously while using electrical contacts
to operate various systems which can make diagnosing stalling problems tedious.
An electrical circuit that is starting to fail will do so more when the circuit
is warm or hot. Signs of heated or melted connections have high resistance and could
cause a shorted connection.