I have a situation on a 2009 Sierra with an LY6 where it starts and runs fine until it warms up and then it shuts off and most times with throw a P0016 code. I can see the event on the scanner when it happens and t does show the cam retarding fully at idle and then not returning until it cools off. I scoped the cam and crank with a Picoscope and I can see the cam runs 8 degrees retarded at idle when it correctly running. This jives with a known good scan. Then when the event happens, it goes fully retarded to 60 degrees in relation the crank. The phaser can retard 52 degrees so that lines up (60-8=52). It will stay there and will crank all day long and won't start and won't return to park. The only thing I can think of is that the phaser is hydraulically locked and eventually the oil bleeds out.

I opened up the front cover and everything looked great for a 212,000 mile motor. I went ahead and replaced the phaser, crank sprocket, tensioner, chain, oil pump and cam bolt (all melling). Also replaced the cam sensor and crank sensor with GM parts and VVT solenoid. No change. Now mechanically, I don't see anyway the phaser can retard the cam without oil pressure forcing it to do so. By retarding, it rotates the cam ahead (clockwise) of the outer sprocket. The ECM is not commanding it to do so according to the scanner when it happens. So is it picking up stray voltage and energizing the VVT solenoid?

My next plan of attack is to disconnect the VVT solenoid and disable the VVT in the PCM with HP Tuners. This should keep the phaser in the packed position and keep it from throwing a code. If that doesn't work, then I know that somehow the phaser can retard the cam without oil pressure which makes no sense. Then my plan would be to install a phaser lockout and call it a day. It's just a farm truck so I just need it to run but I really want to know what is causing this.

Has ANYONE ever heard of a situation like this?

 

What is ypur oil pressure?

The phaser has advance and retard cavities in it.

Oil pressure goes to advance the cam with zero duty cycle from the magnet upto 50 percent duty

50 percent duty holds cam stationary to phaser

Over 50 to 100 percent flows oil to retard cavities

 

The phaser has a locking pin that should only unlock and let it retard the timing if oil is supplied through the retard ports of the valve(cam bolt)

If your phaser/valve/magnet are new and good unplugging the magnet should keep it from unlocking and retarding the timing

 

My sister in law's cam was 'Tarded- She's a Pilot now.

 

Oil pressure is 20 psi at a hot idle and 45 psi at about 2000 rpm. I would agree that unless commanded, it should be parked and locked with the pin. Mine is not as it will fully retard when hot and idling. It takes about 30 minutes of running and then the cam instantly retards and it stalls and will not start until it cools down. Very, very strange.

 

Leave the magnet unplugged and see if it happens

 

Still happens with VVT unplugged and VVT coded out of the ECM. As soon as it gets up to operating temp, it’s not long where it goes out of phase and it stalls. It will not restart until it cools. Using a pico scope, I can verify it’s locked in the full advanced position. Using AI, it was describing a phenomenon where the rotor can advance uncommanded if the oil pressure can’t hold the lock pin. Cam torque pulses actually bias the advanced position and can overcome the internal spring. This seems far fetched but would explain my symptoms perfectly. So my next step is to install a comp cams phaser lock kit so I know 100% it can’t move and that will confirm the cam pulse theory. No good resources on this.