1999 Mercury Cougar Stall on left turn with quarter tank

Hello nudijoel

Fuel injected engines are very sensitive to fuel pressure as well as fuel volume. Low pressure will cause starting and driveability problems. A pump that can deliver adequate pressure but not enough volume may allow the engine to start and idle normally, but it will starve the engine for fuel and cause a loss of power when the engine is under load. Certain scan tool can show fuel pump pressure but not fuel volume. If fuel volume is good, checks the operation of the fuel pressure regulator to make sure it changes line pressure in response to changes in engine vacuum. This is necessary to maintain the proper operating pressure behind the injectors and to compensate for changes in engine load:
for example turning the steering or making a turn, turning AC on.
Check the charging voltage to start with.