Hard Starting Engine

Step by step instructions on how to repair an automotive engine that cranks excessively before running (hard starting), this article pertains to most cars.

Difficulty Scale: 5 of 10

The definition of hard starting is, when the ignition key is turned to the crank position, the engine takes longer than usual before it will start and run, (Extended crank time). When an engine is cranked over it should fire up within a two to three second interval. Before troubleshooting begins, park the car on level ground, with the emergency brake set.

Automotive Engine
Step 1 - For an automotive engine to start and run correctly the engine tune up must be kept up to date.

New Spark Plug
Step 2 - The fuel system must quickly pressurize for the engine to start, it also needs to be able to hold pressure for a short time while the engine is turned off.  Perform a fuel pressure and regulator test using a fuel pressure gauge. Its also a good idea to remove the fuel filter to check for blockage. (Tip: If you suspect the fuel pump has a problem, a trick is to cycle the ignition key several times with out starting the engine to build line pressure, if the engine starts without extended cranking the fuel pump is weak and needs replacement. Visit - Fuel pump replacement

Fuel Pressure Test Gauge
Step 3 - An engine depends on vacuum to allow the engine to start up and run properly, if there are leaks in the vacuum lines the engine will have an extended crank time before starting. Inspect the engine's vacuum lines and repair broken or dilapidated lines.

Vacuum Line
Step 4 - At the air intake port of the engine known as the throttle control motor or throttle bore, mass volumes of air leave deposits called coking. These impurities pass through the engine despite the air filter and build up over time. Servicing this unit as part of a regular tune up is necessary for proper operation. Visit - Throttle actuator service

Throttle Actuator Cut-Away
Step 5 - The idle air control motor adjusts the amount of air via the computer released into the engine at idle. This device is subject to coking much like the throttle bore. To check this condition remove the IAC motor and inspect, if the plunger of the motor has deposits, clean with carburetor spray or replace the motor with a new unit. Also, clean the air passages with cleaner before re-installing the idle air control motor. Visit - Idle air control motor replacement

Idle Air Control
Step 6 - The air intake boot connects to the throttle body of the engine and if torn or broken creates a lean fuel/air mixture causing excessive cranking. Inspect the air intake boot from the throttle body to the mass air flow meter.

Reinstalling Inspected Air Intake Boot
Step 7 - A fuel pressure regulator regulates fuel pressure to the engine injection system. If a fuel pressure regulator diaphragm ruptures it can allow raw fuel into the engine through the vacuum feed line attached to the intake manifold. To check the fuel pressure regulator for this condition remove the vacuum line from the regulator and check for the presence of fuel inside the vacuum line, if fuel is present, replacement of the regulator is needed.

Fuel Pressure Regulator Check
Step 8 - The car's computer system utilizes both crankshaft and camshaft sensors to evaluate the engine as it cranks over to synchronize ignition and fuel injector pulse. If the crankshaft sensor fails the computer will use the camshaft sensor as a single reference which can cause hard starting. This condition is usually accompanied by a check engine light code number P0335. Replace the crankshaft angle sensor.

Crankshaft Angle Sensor
Step 9 - Engine cylinder compression is needed for an engine to run properly. Once an engine has reached its life expectancy the compression drops due to piston ring and cylinder bore wear causing a longer than normal crank time. Perform a compression test to check for this condition.

Piston Rings
Step 10 - If a starter is weak it can cause the engine to crank slower than usual, which causes the engine to build compression slowly. This can be caused by a weak battery or starter motor. Visit - Battery load testing and Starter motor replacement


Best Practices

  • Regular engine tunes up's and fuel filter replacement can stem hard starting conditions.
  • To prevent engine cylinder low compression change motor oil and filter at recommended intervals.
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