1998 BMW 740IL P0170 Fuel Trim Malfunction
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Customer Concern: Tests/Procedures: Potential Causes: Tech Tips: P0170 Fuel Trim Malfunction (Bank 1) P0173 Fuel Trim Malfunction (Bank 2) 1. Check for an intake air leak in the throttle body, intake runner gaskets and Positive Crankcase Ventilation (PCV) valve. The best time to check for intake leaks is when the engine is cold, as the gaskets tend to seal up as they expand after warm up. 2. A smoke machine can be used to check for leaks, or the intake area can be pressurized with regulated shop air to 10 PSI or pounds per square inch.
Customer Concern: Tests/Procedures: Potential Causes: Tech Tips: P0170 Fuel Trim Malfunction (Bank 1) P0173 Fuel Trim Malfunction (Bank 2) 1. Check for an intake air leak in the throttle body, intake runner gaskets and Positive Crankcase Ventilation (PCV) valve. The best time to check for intake leaks is when the engine is cold, as the gaskets tend to seal up as they expand after warm up. 2. A smoke machine can be used to check for leaks, or the intake area can be pressurized with regulated shop air to 10 PSI or pounds per square inch.
Then spray around the throttle body with soapy water and look for bubbles. 3. Check the PCV system by testing the crankcase vacuum.
It should be from 8 to 15 millibar (that equals about 1/4 to 1/2 inch
PSI of vacuum). It can be checked at the oil dip stick tube.
Insufficient Fuel Pressure Intake Runner Gaskets. Leaking PCV Valve
Leaking Positive Crankcase Ventilation (PCV) System Leaking Throttle
Body If leaks are found in the PCV system or in the intake gaskets, would recommend making repairs in both areas unless they have been recently replaced.
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