Power Surging

[KZCool]

I've noticed a very annoying thing lately.  When I'm driving on the highway in 5th gear (MT) and apply full throttle I can feel the power increase from the VVL, but I notice that sometimes it pulses and doesn't want to apply smoothly.  This causes a slight power surging and if I slowly let off the gas I feel a point that actually accelerates better with less throttle.  Could this be a bad VVL solenoid, or something with the fuel mixture? Im at a loss.  It seems like bad engineering to use two separate oil pressure sensors for the VVL system since oil pressures could be different on the two sides of the engine, so the VVL system doesn't engage at the same time.

[GeneralDisorder]

It doesn't use oil pressure sensors. It uses duty solenoids to regulate pressure to the AVLS rockers, and switches to confirm the duty solenoids are activating and that pressure is being fed to the rockers. The system in not particularly pressure sensitive, and at the RPM it kicks in the engine oil pressure is more than sufficient to actuate the rockers. They are on or off, not variable. Further the oil pressure will not be significantly different on either side of the engine, unless the engine is clapped out, in which case it really doesn't matter if this system works or not. 

GD

[KZCool]

So the oil pressure sensors verify that the duty solenoids are working correctly? they aren't the sending units for the on/off signal of the solenoid? 

[GeneralDisorder]

The oil pressure switches are there to tell the ECU if oil pressure is getting through the duty solenoids. That's why you get a code 26/28 when the switch fails but the code is actually an AVLS duty solenoid performance code because the ECU has no way to detect a switch failure (or low oil pressure for that matter). Ironically it's always the switches that fail - often leaking large amounts of oil from the harness connector.

The system has no need for variable pressure as it can only be in the locked or unlocked positions. It has no way to vary the lift on the secondary rocker - it either uses the small lobe for secondary rocker lift, or locks the secondary rocker to the primary rocker and both use the high lift lobe.

Edited September 9, 2018 by GeneralDisorder

[KZCool]

Yeah, one of my switches had failed and I tightened the sensor too much cracking the head......right after I put the motor back in from changing the head gaskets.  I had to tap threads deeper and put in an adapter pipe that the sensor could screw into. Horrible design having the sensor hole an extrusion off of the side of the head.  It may have actually been the duty solenoid then if I'm still getting the code and the surging. 

[GeneralDisorder]

The only time we have had that problem is when the 200 lb gorilla on the tool over torques the sensor and breaks the head. I have had to weld that problem twice. We have done hundreds of these head gaskets though and anyone that has happened to has only done it once. If you are getting the code after that mess, then like as not there is a blockage related to the tapping, or whatever other machining operations occured to rectify the "accident".

You should remove the duty solenoids and their adapter plate. There is a screen filter under the plate that should be checked. 

Having a keen sense of the torque required for an 1/8" BSPT thread and using the proper sealant is absolutely critical here. Inch pounds torque wrench is highly recommended if you aren't 100% comfortable with this size of fitting. 

Edited September 9, 2018 by GeneralDisorder