All computerised cars basically do the same thing at startup. With
the key on, but engine off (i.e. not in the "start" position), the fuel
pump should activate for about 2 seconds to prime and
pressurize the fuel system. If you roll the key straight to the start
position, it still performs this prime function while trying to start. It
also does this to provide fuel pressure REGARDLESS of the oil
pressure. Now, if during startup, the computer (ECM or PCM)
detects an adverse condition that could cause damage to the
drivetrain, it will inhibit the signal that activates the "fuel pump
relay", and subsequently, the "fuel pump". Side note* Most people
think the fuel pump is activated directly from the computer. Not
the case! It can't handle the necessary current needed to drive
the pump. With "that" said, several of the conditions that would
cause the fuel pump signal to be inhibited are "low oil pressure"
and "wide open throttle". The latter is vastly more important than
the first, and so, the computer will not provide fuel to an engine it
thinks is set to redline, and then grenade your engine. Now, the
throttle position is just a sensation provided to the computer so
that it can adjust various things like a/f ratio, ignition timing, shift
points, etc... The TBI "mechanically" acts like a carburetor
regardless of the status of the throttle position sensor (TPS),
meaning that when you put fuel or spray ether into the throttle
body, it will generally start if it gets a spark and the oil pressure
rises. If it starts and runs at this point, your "Oil Pressure Sensor"
is fine and your "TPS" is suspect. If it starts and runs for a few
seconds, and then shuts off, your "Oil Pressure Sensor" is
suspect. I hope this helps. Philip
1 people found this helpful.