Cm870 running on back 3 cylinders

[BrianL]

Hello, I need help on where to start. My 2003 Isx only running on the back 3 cylinders.
Here’s what I have done. Swapped the timing and fueling actuators front to back with no change, still runs on the back cylinders. Next I got the injector leak tester and found the #1 injector to produce bubbles on the compression stroke so I replaced the injector, still no change, it only runs on back 3. Next I sent the ECM to {aftergarbage ecm repair shop} for testing and they determined it was bad and not repairable so they sent me a remanufactured one for $1300 and guess what, the truck still only runs on the back 3! Any ideas where to start next?