Hi Guys. The Vf output has three different types of Vf output.



OXYGEN SENSOR FEEDBACK MODE

DIAGNOSTIC MODE

LEARNED VALUE MODE



see below for details





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#1

Oxygen Sensor Feedback Mode.



T and E1 Connected

Idle contact point off

Engine at 2500 rpm



Result of 0x sensor signal processing

5v.......Rich



or 



0v........Lean

0v...........Open loop condition





_______________

#2

Diagnostic Mode



T and E1 connected

Idle contact point On

Engine off



Results of Diagnosis

5v........Normal



0v........Trouble code stored





________________

#3

Learned Value Mode



T and E1 not connected

Any Speed



Result of Air-Fuel ratio voltage feedback



0v...........Rich

1.25v.........Normal

2.5v...............Normal

3.75v.........Normal

5v...... ...Lean





Learned Value is



It is a fuel injection correction coefficient which tailors the standard

fuel injection duration to minor differences between engines due to

manufacturing tolerances, wear, and minor mixtures disturbances like

small vacuum leaks.



This coefficient is capable of altering the calculated injection {before Ox

correction} by as much as 20% to prevent Ox sensor correction from being

excessive.



If you encounter a driveability problem that sets no codes, this Vf voltage

feedback can be of some help. Especially code 25/26. {engine condition

rich or lean}



Note:

Discard Vf reading when engine is cold.

The Vf learned value tells you how hard the ECU is working to keep the

engine running properly.

After loss of power to ECM, it will take a certain amount of time to

relearn, depending on the engine model and vehicle driving conditions.

The ECM will learn faster if the input signals are stable <Water Temp,

Air Temp, Throttle position sensor, Air, Ox etc>

At high altitude operation, Vf can be 0v but it is considered to be normal

{lack of oxygen}

Vf voltage reading may be different, depending on accuracy of voltmeter,

and connections. However, the number of steps 5 are still the same. {e.g.

1.10v instead of 1.25, 2.2v instead of 2.5v, 3.5v instead of 3.75v}

Vf voltage can be "border line" also, flipping back and forth between 2

ranges.







_______________

Learned value mode fuel trim conditions





0v                            1.25v                        2.5v                    3.75v                         

5v

Rich                         Normal                     Normal                Normal                      

Lean



Ecu                            Ecu                             +/-                   Ecu                             

Ecu

decreases                  decreases                     3%                   Increase                     

Increase

fuel by                      fuel by                                                  fuel by                       

fuel by

11%-20%               4%-10%                                             4%-10%                  

11%-20%









I hope this will help with questions with the Vf output signal









Reg