I have a '99 GMC pickup with the 5.3 Vortec that has an intermittent
starting problem. The engine will not restart under various conditions.
After long crank times and jump starting the engine will start. On other
occasions the engine will restart and then die as soon as the ignition
switch is returned to the run position. I have ruled out the fuel pumps and
the relay. There are no diagnostic codes that are tripping the MIL lamp. I
don't have any way of retrieving the codes from an OBD2 system. The only
item that I inspected that seemed to resolve the start/die problem was the
airflow sensor. After inspecting the airflow sensor the engine started and
continued to run. This may have just been a coincidence as I didn't find
anything noticeable problem with the sensor. Any help with this problem
would be greatly appreciated.
The initial start sequence is handled by the ignition module and once
started, the controls are handed to the ECM. That engine, If I recall
correctly, should start within one revolution of the crank shaft. ( this
means very quickly ). If it takes several turns of the crank before it
starts then it has defaulted to a backup start. This means that possibly
either the crank, or cam shaft sensor is not working. If it does start right
away and then dies, then you might be on the right path with the MAF sensor.
The initial starting sequence does not look at the MAF sensor, but is needed
for normal operation.
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