Atlas 4.2L LL8 Exhaust Camshaft Position Actuator - (CMP) Sensor - VVT Cam Phaser - DIAGNOSIS/BENCH TEST/FINAL INSTALL ORIENTATION

[808]

Salutations Brothers Of The Wrench!!!

In completing a ****Finalized Comprehensive**** compilation of all influences directly relative to the Vortec 4200 L6 Engine VVT Variable Cam Phaser System, I found a wealth of knowledge deposited across the years within a number of forums, articles, and formal GM releases directly correlative to and updating all discussion and subtleties hidden within and surrounding this exceptionally complex system.

Beginning at timestamp 5:30, this video:

General Motors - 4200 Engine Familiarization​

begins an original introduction of the variable cam phaser system incorporated *within* the exhaust cam sprocket as the:
"Exhaust Camshaft Position Actuator".

This integral component is the fundamental backbone of all valvetrain viability, vulnerability, and specialized DOHC timing retardation.
FINAL focus of the PCM's p.ulse-w.idth-m.odulated variability to valve overlap is tucked away in the hub, whereupon is found a:

Hydraulically Actuated Piston.

This piston is **first-feed-fed** by it's fundamentally integrated *neighbor* :

The Camshaft Position Actuator ***Solenoid***.

This solenoid -in- PRIMARY- PCM p.w.m. focus directs the CMP timing retardation based on hydraulic principle actuation.


From the GM Video:
"The piston has an internal helical spline that slides enmeshed with the gear, as the piston moves, the piston and gear mechanism changes the timing of the exhaust camshaft relative to the camdrive sprocket."

::::: PRIMARY FOCUS OF THIS POST :::::: :

--- "When oil pressure is applied to one side of the piston, the cam moves ^clockwise^, and timing is advanced." ---

--- "When oil pressure is applied to the other side of the piston, the cam moves *counter clockwise* to retard timing." ---

--- "The total range of camshaft phaser rotation is 25 camshaft degrees"---

Video Example at timestamp 7:17 :
--- "When the 4200 is at idle, the exhaust cam is in the fully advanced position...."
At this point in the video, using the exhaust camshaft HEX, the exhaust #camshaft# is rotated CLOCKWISE to demonstrate the:

"FULLY ADVANCED" position.

As the camshaft is rotated clockwise in the video, it can be clearly seen that the *ACTUATOR* outer ring/ front reluctor advances clockwise & *LOCKS* 99% independently of THE SPROCKET, and *ONLY BARELY MOVES* the cog orientation in the timing chain configuration as it locks in fully advanced orientation.

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I'm writing this post to advance a cumulative response to the *GREY* area of what has been considered as a "fully advanced" phaser in the *viable configuration* of orientation, and to surgically remark on $ it's exacting finality $. @Mooseman & @mrrsm have both drawn excellent dissertations related to this subject, and I would state that both have described the exact nature of this component directly relative to the R&R of the timing system.
___________________________________________________________________

Relative to the:

2008 4.2L Manual (2005 & Onward 4 Vane Style Actuator)

PAGE 68,

CAMSHAFT POSITION ACTUATOR DIAGNOSIS

The camshaft position actuator will only phase 25-cam degrees retard(counterclockwise). Full advance clockwise is 0 degrees.

The camshaft position actuator should always be serviced/replaced in the full advanced position(full clockwise or 0 degrees).

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New replacement(service) camshaft position actuators are ^^^^^shipped at full advance or 0 degrees.
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To be sure the camshaft position actuator is performing properly, perform the following to help in the diagnostics.

The camshaft position actuator must be removed from the engine to perform the proper diagnostic test.

1. Clamp the camshaft actuator in a vise. Use care not to damage the contact area of the sprocket.
2. Scribe or draw a line on the camshaft position actuator outer ring face, in the full advanced position.
With the engine at TDC, on #1 cylinder, the wording should be level.
3. Apply compressed air pressure to the oil port(1) on the back side of the actuator to UNLOCK THE LOCKING PIN.

####808's Case Study Note:####
When applying compressed air to the rear oil port, it's obviously redundant to observe a rubber fitting at the source of air contact.

Subtlety at pressure activation:

Compressed air applied -will- slightly unlock the actuator, but without holding the actuator **FULLY ADVANCED** clockwise during ***initial*** application of compressed air, and then by turning to full counterclockwise position, only a minute degree of rotation was possibly achieved.
#########################

4.Turn the actuator, by hand, to the full counterclockwise position.
5.Scribe or draw a line on the camshaft position actuator at that position.

IMPORTANT: It is normal for oil and air to leak out of the camshaft actuator when compressed air is applied. It is also normal for oil bubbles to form on the camshaft sprocket surface due to porositY caused by the casting process. Do not replace the actuator due to this leakage.

6.Measure the distance between the two lines. The measurement should be 14-15mm (0.55-0.59 in).

++++The camshaft position actuator must be replaced IF: ++++++

IT DOES NOT UNLOCK WHEN AIR PRESSURE IS APPLIED,
DOES NOT LOCK WHEN AIR PRESSURE IS REMOVED,
OR DOES NOT MOVE WITHIN THE 14-15 mm(0.55-0.59)

++++++++++++++++++++++++++++++++++++++++++++

HEREIN CORRELATED WITH:

TSB 07-06-01-018A:
Vortec™ 4.2L I-6 Engine (VIN S — RPO LL8)
This bulletin is being revised to remove reference to the parts information. Please discard
Corporate Bulletin Number 07-06-01-018 (Section 06 — Engine/Propulsion System).

Engine Cylinder Head Installation, Step 4

Exhaust Camshaft Actuator Notice: The exhaust camshaft actuator must be fully advanced
during installation. Engine damage may occur if the camshaft actuator is not fully
advanced. Refer to Camshaft Position Actuator Diagnosis in SI.


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With this Data Set,

The visual representations, written descriptions, and firsthand accounts all describe and directly indicate that:

the VVT Phaser, in a -locked- position, requires a hydraulically or pneumatically actuated stimulus to:

*UNLOCK*

from

* A FULLY ADVANCED POSITION OF 0° *

Thus, if the actuator is LOCKED, it is FULLY ADVANCED TO ZERO°.


Here follow 2 photos,
1st: The antiquated phaser of 185,000 miles of use, demonstrating worn cogs, 19.5mm of travel, inability to lock, and minor particulate expulsion from the vanes at the compressed air blast out.

2nd: Declarative Statement & "New" GM VVT Phaser - appropriated from the box *in dire straits* of strange powdered metal.

 

[808]

I would be remiss not to point towards the excellent article written by Dave Hobbs, published in the August 2009 issue of MOTOR.

GM S VARIABLE VALVE TIMING - PDF Free Download

NEW TWIST ON AN OLD STORY: GM S VARIABLE VALVE TIMING BY DAVE HOBBS Powertrain engineers continue to extract more power from and reduce emissions on conventional internal combustion engines. When both

docplayer.net

 

[Mooseman]

@Mooseman & @mrrsm have both drawn excellent dissertations related to this subject, and I would state that both have described the exact nature of this component directly relative to the R&R of the timing system.

All I've done is open it up and replace said components. I know it works by oil pressure controlled by the PCM via the CPAS. The rest is total voodoo to me.

 

[808]

All I've done is open it up and replace said components. I know it works by oil pressure controlled by the PCM via the CPAS. The rest is total voodoo to me.

Talk about voooOOooOooDOOOO!!!! lololol!!! Brother I cannot thank you enough for sharing your invaluable experiential data on this specific topic, it's been absolutely clinch!!! The "quorum" for expository surrounding ***this*** specific nicety of definition in our contemporary timeline has been somewhat "mythical".

As you well know, DTC's p0017 & p0016 must be anticipated, regarded & abated ???300???400???? steps in advance before completely rebuilding the engine&vehicle again.

 

[808]

Elaborating on this point, linking a few videos that follow up directly related to the PLAUSIBLE RAMIFICATIONS of uncertainty surrounding this orientation issue, covered in:
Bulletin No.: PIP4945B
Date: Mar-2015
Subject: Inline 4 5 And 6 Cylinder Engines With P0017

Bulletin No.: PIP4913A
Date: Nov-2015
Subject: SES Light Intermittent DTC P0017 After Cylinder Head Replacement Engine Oil Debris Contamination

+++++++++1st Video - Gibson Garage Speed Shop

How to test timing advance actuator on 04 Envoy Trailblazer​

@ Timestamp 0:50 Mr. Gibson Garage Speed Shop Quotes:
"I found a way to test it I think, with it still installed,
***BUT I DID HAVE TO TAKE IT ALL APART AGAIN***,
the oil pan, *everything*.
In his findings on removal of the front cover & investigation of the timing system fastener conditions, the timing chain tensioner bolts in question were discovered to be *loose* in their thread schedules.

His transparency on the matter is excellent, as he states that he can't be certain as to whether or not he forgot to tighten the bolts, or they backed off under load, but his level of consideration of finality in this rebuild resolves to the use of threadlocker @ these thread ports *in answer*.

I recognize this instance of adhesive application is a departure from the factory manual protocols, concerning thread testing, helicoils, etc. , yet, as all service technicians know *very clearly*, if there has been some "MALARKEY" halting the *fundamentals* of getting the engine back to CHOO CHOOOOOOOOO mode,

the reciprocal, may, in fact, be a TOUCH of glue to those lbs ft. after a solvent, to ensure *SOLVENCY*. (18lbf-ft to be exact for these fasteners).

*In Formality* :
I do not promote or endorse random use of thread locker compound, or a departure from OEM spec.
*
This being said, he gives an excellent view/confirms of a number of specific *orifi* correlative to first feed filtered oil pressure, and how the feed directly interacts with the oil feed of the ^Timing Chain Tensioner Actuation^. All of which are very helpful to regard fling angle and first flow path from the Gerotor's direct pumping force.

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*ALSO* I'd like to take a moment to recognize the internal drilling of the VVT actuator solenoid port into the head directly beneath the exhaust camshaft that is depicted in this video(of which we see in a **SOLVENT** scenario, in good shape, without any visually noted impending *rupture* condition:

***AT THE END OF THE DEPTH OF THIS PORT PROJECTION INTO THE MAIN VALVETRAIN FLOW***

*There may have been an opportunity for the long term operation of the VVT solenoid to

*****PUNCH*****

95%-99% of it's way through an extremely thin wall endo into it's furthest travel of actuation
- directly through this camshaft cap pillar - .

At this exact location in question, there may possibly be a monster aluminum flake waiting to shear off and find it's way downstream.
I recommend checking the finish of this specific port and verifying that this situation has been either mitigated by an exacting milling procedure at the time of production, or now, in conflict resolution before further mileage inquires upon the *potential*.
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Moving forward, @ timestamp 05:46, He posits that the code thrown relative to the advancement of the specific VVT Actuator "was because of the leak there, it wasn't tight, make sure that timing tensioner is tight, a leak there, I think would definitely affect the pressure situation up in here.."-->(the VVT feed from the exhaust camshaft is in visual depiction at this point in the video).

-afaik-, based on his youtube commentary&followup, this issue was never remedied.
The Code Remained.

++++++++++2nd Video:
South Main Auto Repair

Chevy Colorado P0017 Case Study Part 3​

To be obviously redundant, this vehicle, is, of course, an '06 2.8L L4 LK5, not a 4.2L LL8.
GMT Family Regard.

@Timestamp 51:15, Mr. South Main Auto Repair Quotes:
"So I printed out the paperwork as far as what GM considers a test, now they do say here in the paperwork that the camshaft position actuator will phase 25 cam degrees retard counterclockwise, full advance clockwise is 0 degrees, so it's natural resting position is 0 degrees and locked."

At this point in the video, we see that he has vise clamped the sprocket of the VVT actuator of this Chevrolet Colorado in question, and is manipulating it by hand with a pronounced "clicking" sound that can clearly&easily be heard, seen, etc.


*I'd like to state that this depicted onscreen instance is an excellent visual example of an already **UNLOCKED** actuator.

The remainder of the performance methodology here, of *this* instance of potential test, imho, would be appropriately described as more effectively considered "destructive testing" for a VVT CMP that would already be considered as garbage, not to be reused.

The *OUT OF THE BOX* orientation of a fresh GM VVT Actuator for the 2008 Chevrolet Trailblazer should be - Fort Knox, 0°(ALL VVT's SHIPPED FULLY ADVANCED. This to be OEM spec.