VVT Solenoid. How does it work?

coolride

Original poster
Member
Aug 23, 2019
596
Adirondacks
How does the VVT solenoid function? Does it change cam timing continuously or does it "shift gears" between two or three settings?
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
Unlike its other 'Square Wave Sensor Brethren"... The Variable Valve Timing Solenoid uses an electromagnetic coil with a Smooth Plunger...indistinguishable to the Solenoid on the Starter Motor, but much more active in shuttling Motor Oil Into and Out of the Exhaust Camshaft Phaser. The range of this subtle movement of the plunger can adjust the Exhaust Camshaft from Zero to Twenty-Five Degrees.

The additional Oil Pressure on either side of the Inlet and Outlet Channels in the Body of the VVT Solenoid determines whether Oil Enters or Exits the Original Helical Gears hidden inside of the early model Cam Phasers that move in adjusted positions to advance or retard the Exhaust Camshaft in its relationship with the Crankshaft and Intake Camshaft positions. This GM Atlas 4.2L Passenger Side Engine Head-Cam Phaser Cut-A-Way Illustrates the VVT Solenoid position ...and the Phaser's "Innards":

GMATLAS42LENGINEHEADCUTAWAY.jpg

This allows the Cam Phaser to work within an infinite number of Variable Cam Retarding Positions between 0-25 Degrees; acting as a both the means to shift the Power Band completely independent of all the OTHER Square Wave Outputs to the PCM. In this way it can make micro-adjustment from Idle conditions well up into the higher RPM bands. This variability greatly improves the performance of the GM 4.2L Atlas Engines. At idle the VVT Solenoid allows the engine to run as though it is an Exhaust Gas Re-circulation Valve (EGR).

The Failure Modes of the Variable Valve Timing Solenoid are as follows:

(1) Poorly Maintained Engine Oil Change Maintenance invites Clogged VVT Screens.
(2) Totally Clogged Stainless Steel Screens in the Input and Output Channels.
(3) Loss of the Filter Screens ...either getting ingested into the Cam Phaser or Oil Pan.
(4) Motor Oil Invading the Electrical Connector.
(5) Failing "O" Ring Seal causing Motor Oil to Leak down the Right side of the Block.
(6) During VVT R&Rs... Fresh Motor Oil and Oil Filter Changes are a MUST.
(7) Engine Oil Flushing (6 Qts Motor Oil to 1 Qt Trans Fluid) can help to clean the passages.
 
Last edited:

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
And how that oil pressure moves the cam phaser is shown here:

 

Forum Statistics

Threads
23,273
Posts
637,484
Members
18,472
Latest member
MissCrutcher

Members Online