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Yesterday I got a P0012 code for intake cam position over retarded so I hooked up my MPVI2 and logged the intake cam positions. At first I was surprised to see the swings in cam timing vs the desired 30 degree as the exhaust timing is nearly exact at all times. There wasn't much info on the web about normal VCT operation but what little I did find also showed a similar waveform. It also looks like the timing is compensating up to 30 degrees of advance when the cams advance. I'll say that the truck appears to idle fine as long as cam 1 (green) and cam 2 (red) are in sync, when cam 2 diverges from cam 1 is when I notice a momentary rough idle. I'm not sure yet if cam 1 or cam 2 corresponds with P0012 (bank 1), I'm leaning to cam 2 because it appears to be more erratic. I also had a short time when I cam up to 2000RPM and the waveform tightened up, not sure if I have a low idle oil pressure and the phasers aren't operating as intended. Aside from the random rough idle the truck seems to run fine, mileage is consistent and hasn't lost any power. I'm looking for any advice from anybody that has VCT logging experience to let me know if this is normal. Ripping into the motor to randomly replace solenoids or phasers is not my first choice as it hasn't impacted drivability and that doesn't always appear to be a sure fix. For reference the truck has a gen 3 5.0.
UPDATE: I ran another log including Oil Pressure and noticed a couple of things.
- Idle OP is 10-15 PSI (within range)
- 2000RPM OP is 30-40 PSI (within range)
- at 2800 RPM OP jumps to 60-75 PSI
At higher RPM the actual cam timing matches desired almost perfectly. I don't know if this is due to the higher oil pressure or possibly different VCT tables at higher RPM. Here is a screenshot of a run to redline with oil pressure and intake cam angles plotted. Thoughts?
This guy goes in to great depth about VCT's and how to diagnose problems. Doesn't waste of lot of time hemming and hawing either. Watch the 2nd video on the list, at least.
VCT Logging Results - Need Input
