Hello!
What you are describing is consistent with fuel pressure loss. The fuel system must retain pressure after teh engine is shut off, so that fuel is immediately available for starting the engine the next time. If pressure is slowly bleeding down overnight, it will cause symptoms just like you are experiencing. If the fuel is being lost into a cylinder due to a dripping injector, it will also cause a momentary rich condition upon inital startup as all of the extra fuel in the cylinder burns at once.
This type of fault can be diagnosed by connecting a fuel pressure gauge to the rail and monitoring fuel pressure after the engine is shut off. Fuel pressure should still be present the next morning when you go out to start the car; if it has lost pressure there is a fault in the system. Pressure loss in a fuul injection system can occur back through a worn fuel pump, through a faulty fuel injector(s), or past a faulty fuel pressure regulator.
This type of fault rarely causes any fault codes to be set as the computer does not monitor fuel pressure. It does not begin to monitor fuel mixture untill the oxygen sensor warms to operating temperature (around 750 degrees F). By this time, the symptoms are gone.
I hope this is helpful; if so, please click my accept button! Thanks!
Edited by Steve7654 on June 14 2006 at 12:24pm
