The ECU Job Comes to SP from GTA online, with this mod you can play the full ECU Job recreated from GTAO Tuner Update.
To start the ECU Job you will need to enable MP maps via a trainer or another mod like EAI, then, if go to the marked yellow autoshop blip (if you have LCC business installed go to your purchased autoshop from that mod instead), go up to the planning board in the autoshop and press E when prompted to start the ECU Job.
The mod has a Phone contact for you to change location of your autoshop, and to adjust difficulty of the mod.