no power under load + backfires - fuel pressure? ignition? sensors/ecu?

[geezer101]

4G64 doesn't have a vacuum advance - all controlled by the ECU. You need to do some basic checks. First see if you are getting ANY codes from the ECU that indicate a fault. The ECU's themselves are notorious for failing but are not a nightmare to fix or diagnose. Cracking the ECU case open and a visual inspection usually reveals bad capacitors or worse case scenario bad tracks on the PCB. If the ECU has failed, it will operate in 'limp home' mode which means it'll run, but not be happy about it.