Looking for some help diagnosing an ongoing issue that hasn’t been resolved even after a PCM repair.
Truck: 2005 Ford F-150 Lariat, 5.4 Triton
Symptoms:
Rough idle
Stuttering at highway speeds
Poor fuel economy
Engine feels smoother at higher RPMs but lacks power overall
Ticking noise that was not present before
Codes:
P0605 (PCM ROM error) – consistent, triggers check engine light
P0325 (knock sensor) – intermittent, does not always trigger CEL
Previously saw P1000 after resets (cleared once drive cycle completed)
What’s been done:
Full timing chain kit replacement (including phasers and solenoids)
PCM sent out for repair/reflash (G7 Computers)
After reinstall:
Truck initially ran well
No check engine light
Smooth operation
Current issue:
After sitting overnight, on next cold start:
Check engine light returned
Similar drivability issues began again
PCM reset temporarily improves performance, but degrades again within ~30 seconds or next drive cycle
Electrical observations:
Battery:
~12.5V engine off
~14.3V running
At PCM:
Constant power (orange wire) measured ~10.8V (low compared to battery)
Other PCM circuits closer to expected voltage
Ran a temporary direct power feed from battery positive to PCM:
Delayed onset of issues
Truck ran better initially
Additional observations:
Passenger side VCT solenoid unplug test resulted in no noticeable idle change
Engine can hold ~2000 RPM smoothly at first, then begins to degrade
Code does not always return immediately after reset; sometimes delayed
Issue pattern suggests temporary improvement after resets or power changes
Questions:
Has anyone seen P0605 return after a PCM reflash/repair where the root cause was wiring or voltage drop?
Are there known weak points in the PCM power or ground circuits on this generation F-150?
Would a voltage drop in the PCM power feed be enough to trigger or re-trigger a P0605?
Is it more likely the PCM is still faulty, or that the wiring is causing instability and corrupting it?
Next steps being considered:
Full voltage drop testing from battery to PCM under load
Tracing PCM power feed from fuse box for resistance/corrosion
Inspecting and cleaning all engine and chassis grounds
Running a properly fused dedicated power feed to PCM for testing
Trying to avoid replacing the PCM again if the issue is in the wiring or power delivery.
Any insight or similar experiences would be appreciated.