Engine Cranks Excessively
(Definition: the key is turned and the engine is cranking, but it takes longer than usual before the engine to start running.)
A. 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. Most (DPI) direct port inject systems are between 40 psi and 55 psi. If little or no fuel pressure is observed and there is 12 volt power present at the fuel pump, the fuel pump has failed and needs replacing.
B. Test for Fuel System Pressure Bleed Down: With a fuel pressure gauge connected to the fuel rail, turn the key to the on position without starting the engine. You should observe the fuel pressure gauge jump up quickly to operating pressure. Then turn the key off, if the gauge pressure falls quickly it is a sign of a failing fuel pump. Next check the fuel injectors; if the nozzle valve inside of the fuel injector is failing it can cause excess fuel to leak inside the engine causing a rich, hard starting condition.
C. Test Idle Air Control Motor (IAC) An idle air control motor adjusts the amount of air released into the engine when the engine is at idle. This air controller is monitored and adjusted as needed by the ECM. As car mileage increases the IAC motor is subjected to mass amounts of air which contain impurities that leave deposits that can slow or stop the operation of the IAC motor. To check for this condition remove the IAC motor and inspect, if the plunger of the motor has deposits, clean or replace the motor with a new unit. (Note: clean the air passenger ways with an aerosol cleaner before installing the new idle air control motor.)
D. Inspect for Vacuum Leaks: Inspect your engine vacuum hoses and air intake boot for tears or ruptures. If vacuum from the engine is allowed to leak it will cause a lean mixture causing the engine to crank excessively before start up, replace any broken or cracked vacuum lines with new and recheck system.
Failed Air Intake Boot
E. Check Air Intake Boot: Inspect the air intake boot from the throttle body to the mass air flow meter. If torn or broken it will allow the engine to have a lean fuel/air mixture causing excessive cranking. Replace the air intake boot and recheck system.
F. Test for Faulty Fuel Pressure Regulator: If a fuel pressure regulator diagram ruptures it can allow raw fuel into the engine through the vacuum feed line attached to the intake manifold. To check 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 replace the fuel pressure regulator.
G. Test for Low Compression. (For high mileage engines only) Remove a spark plug, insert compression gauge and test. The engine compression should be above 115 p.S.I. If not, the engine with crank longer before enough compression can be generated for ignition.
Thursday, July 23rd, 2009 AT 4:03 AM