AD Understanding Fuel Trims

Fuel Trims are adjusted by feedback to the ECM from?

• Downstream O2 Sensor

• Catalytic converter

• Upstream O2 Sensor

• The injectors

A positive short term fuel trim is caused by?

• Unmetered air entering the engine

• A dribbling injector

• Stuck open purge valve

• A rich fuel air mixture

Short term fuel trims are only adjusted during open loop operation

• True

• False

Changes in fuel trim readings can be caused by?

Click on all that apply

• Poor quality fuel

• Dribbling injector

• Air leak at the Catalytic convertor

• Low Compression

• Blocked injector

Fuel trims should be manually reset after a routine service

• True

• False

If fuel limits are exceeded then:-

• The system will go open loop

• A fuel trim DTC will set

• The system will go into closed loop

• The engine will stop

Long term fuel trims are reset when the ignition is turned off.

• True

• False

Long term fuel trims are based on the activity of?

• Short term fuel trims

• Upstream O2 sensor

• Injector duration

• Downstream O2 sensor

Negative fuel trims are compensating for a rich air fuel ratio

• True

• False

The ideal Long Term Fuel trim is:

• -3 to +3

• 0

• +3

• -3