When was the name of Lyallpur changed to Faisalabad?

When was the name of Lyallpur changed to Faisalabad?

لائل پور کا نام کب بدل کر فیصل آباد رکھا گیا؟
Explanation

The name of Lyallpur was changed to Faisalabad on September 1, 1977. 

Faisalabad, formerly known as Lyallpur, is the third-most-populous city in Pakistan.
Second-largest in the eastern province of Punjab.
*******
Pakistan City old name list
1-        Lyallpur was the old Name of Faisalabad

2-        Mahmood pur was the old Name of Lahore

3-        Kalanchi was the old Name of Karachi

4-        Raj Shahi was the old Name of Islamabad

5-        Persha pur was the old Name of Peshawar

6-        Khan Pur was the old Name of Gujranwala

7-        Cambell pur was the old Name of Attock

8-        Salwan Kot was the old Name of Sialkot

9-        Shal Kot was the old Name of Quetta

10-   Neroon Kot was the old Name of Hyderabad

11-   Khan Garh was the old Name of Jaccoabad

12-   Montgomery was the old Name of Sahiwal

13-   Pepri was the old Name of Bin Qasim

14-   Hindu Bagh was the old Name of Muslim Bagh

15-   Ajodhan pur was the old Name of Pakpatten

16-   Fort Sanemars was the old Name of Zhob

17-   owdayana was the old Name of Swat