What's Wrong With My Car? / Why Does My Engine Stall?

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Why Does My Engine Stall While I Drive?

WARNING! Always have the vehicle under inspection on level ground, in park with the emergency brake on. Always wear protective eyewear, gloves and necessary clothing before inspection or work begins. Never crank an engine over when anyone is near the battery or engine. Always have a operational fire extinguisher close by, obey all first aid instructions in the event of an injury. Never stand in front or behind a vehicle when starting or running. When engine is cranked over keep hands and clothing away from rotating components. Anyone with a heart pacemaker should not perform these test.

When your car is in use, many electronic components are used simultaneously creating electrical contacts to operate the various systems. Due to the many electrical components the operate the these systems make this particular repair sometimes difficult to diagnosis. The malfunction could be from your ignition switch to a fuel pump, but only a number of things can cause this condition. An electrical circuit that is starting to fail will do so more when the circuit is warm or hot. Anytime you find signs of heated or melted connections high resistance is present and could cause a shorted connection. Various mechanical systems can fail causing your engine to stall but the majority of the engine stall problems will be electronic based. The list below provides instructions for testing the most popular problems.

Car Repair Guide Troubleshooting Procedure - READ COMPLETELY BEFORE BEGINNING!

• Step 1 - Anytime you have a problem with electronically controlled components such as an engine, transmission, ABS brake, or SRS (safety restraint system, Air Bag) inspect all fuses using a test light and check the under hood power distribution center and under dash fuse panels. If any signs of heated or melted fuses or fuse holders exist repair or replace as needed. If the fuses test ok continue to the next step. How do I check my car fuses?
   
  
• Step 2 - To check for problems with electronically controlled components such as an engine, transmission, ABS brake, or SRS (safety restraint system, Air Bag) and the fuses test ok a trouble code scan is needed to identify any system trouble. Use a simple scanner tool to retrieve trouble codes and see if any trouble codes gathered relate to the specific problem, like a fuel pump circuit failure code. If a trouble code is present but does not pertain to the immediate problem like a EVAP code ignore it until a later time, after the car is running properly. The reason we repair non-related codes after the engine is running properly is because sometime false codes can be triggered by the engine stalling. Once the engine is running again the code present might cycle and turn itself off. You might say "if the engine stalls shouldn't it have a trouble code?" Sometimes conditions occur that will not be detected by the computer, example: if the air intake boot fails the computer can not detect the failure, so the engine doesn't idle and the computer thinks everything is ok with no codes. If no trouble codes are present proceed to the next step. How do I scan my service engine soon light?
  
  
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  Check Engine Light Scan for Trouble Codes Video

• Step 3 - 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. and most (DPI) direct port inject systems are between 40 psi and 55 psi. 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 owners 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. 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 the relay 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, every manufacturer has a different color wire so 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 which is were the pump is located. Ground the test light and probe (pierce the wire's outer coating with the test light probe 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 online auto repair manual to trace the power source to the relay. If good fuel pressure is present continue to next step. How do I check my fuel pressure?
   
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  Fuel Injection Pressure and Pressure Regulator Test

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• Step 4 - The ignition system in your car ignites the fuel inside the engine's combustion chamber at the optimal time in the piston stroke to produce the most power while emitting the least amount of emissions as possible. There are many configurations of ignition systems but all operate on the same principle, create a low energy field and collapse it onto a high energy coil and that transfers the electrical energy into the secondary ignition system, i.e. coil wire, distributor cap and rotor (if equipped) plug wires and finally the spark plug. This system is triggered by the primary ignition system, this system varies depending on manufacturer but all operate on the same principle by using some kind of low voltage trigger system i.e. crankshaft position sensor (CKP), camshaft position sensor (CAS). This low voltage system (1.5 to 3.0 volts) is amplified to 12 volts by using an ignition module (amplifier) and then transferred to the primary side of the ignition coil. The ECM (engine control module) controls the engine ignition timing by advancing and retarding the primary trigger signal. In older cars points and condenser with a vacuum advance unit performed this job. We have listed the most popular causes for an ignition system to fail or misfire, visit - How do I test the engine ignition system?
   
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  Basic Ignition System Test

• Step 5 - The main ECM power relay carries high amperage and is prone to failure, especially when it is in use for a while and gets hot. If the ECM relay fails it will shut down the engine management system and stall the engine. If you suspect the relay could be failing remove the relay cover and inspect the relay contacts. If the relay contacts look burned and have an ash look to them the relay needs to be replaced. If the relay checks ok proceed to next step. How do I check my car relay?
   
• Step 6 - The battery connection in your car can be loose and vibrating when the car running. This vibration causes the battery terminal to short very rapidly creating a electrical system surge that can cause the engine to stall. The battery cable connection must be clean (free from corrosion) and tightly fastened to allow the flow of electricity from the battery to the starter. With the key in the off position located battery to inspect the battery cable connections. Battery cable connections must be tight and not wiggle on the battery terminal. If the cable is lose remove it and clean, then tighten the cable with a wrench or socket wrench. Use baking soda to neutralize any suspected acid residue before work begins. How do I check my battery connections?
   
• Step 7 - The exhaust system on your car is designed to move exhaust gasses created by the engine to the rear of the car. In this exhaust system is comprised of many parts, among these parts are a muffler and catalytic converter. Either of these parts can break apart internally and cause a temporary blockage of the exhaust system causing the engine to stall. To check for this condition start with the engine cold, then take a rubber mallet and hit the muffler and catalytic converter. There sound be very little rattle sound. If you can hear what sound like rocks inside your exhaust system, remove it and inspect it for internal damage.

  
  Plugged Catalytic Converter from Broken Catalyst Material

• Step 8 - The ignition switch in your car is the main electrical connection for the starter, ignition, computer and accessory systems. This switch is constructed with metal connects that transfer electrical power when the switch is engaged. If these contacts become corroded or overheated and burned they can short circuit causing the engine to stall.
  
• Step 9 - shorted temp or 02 sensor
  
• Step 10 - ECM

Additional Resources

• Why does my engine over heat?

Check Manufacturer Specific Engine Stalls Questions and Answers

Related Subjects

• How Emission Controls Work
• How an Ignition System Works
• Engine Wont Crank Questions
• How Performance Exhaust Works

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