S&T Series Blazer, Bravada, Envoy, Jimmy, Rainier, Trailblazer, Xtreme

Distributor Ignition Systems

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High Voltage Switch (HVS) Ignition System



Description & Operation

The High Voltage Switch (HVS) ignition system, also known as the Enhanced Ignition (EI) system, is used only on the 4.3L engines. Though the names of the system has changed the actual system itself is completely unchanged. The ignition system is controlled by the Vehicle Control Module (VCM). The VCM obtains information from various engine sensors, then uses it to compute the desired spark timing, as well as control the dwell and firing of the ignition coil by way of an ignition control line to the coil driver. The High Voltage Switch (HVS) assembly resembles a distributor, containing both a cap and rotor. But, unlike a distributor ignition system, ignition timing is preset and cannot be adjusted because the HVS is mounted in a fixed position (it cannot be rotated). The HVS provides spark at exactly the right time to ignite the air/fuel mixture producing peak performance and fuel economy. The HVS system is comprised of the following parts:



Vehicle Control Module (VCM)
 
Crankshaft Position Sensor
 
Ignition Coil Driver Module
 
Ignition Coil
 
High Voltage Switch
 

The Vehicle Control Module (VCM, often referred to in the past as an ECM) is located on the right-hand side fenderwell of the vehicle. It is the control center for fuel emissions, automatic transmission control functions and the anti-lock brake system. The VCM constantly monitors information from sensors in the engine and controls the component systems. It is designed to process the various input information, then send the necessary electrical responses. The ignition module that was used on the Distributor Ignition (DI) system is not used. All Ignition Control (IC) and bypass functions are controlled by the VCM.

The Crankshaft Position Sensor (CKP) is a digital sensor that provides reference information to the VCM for spark and fuel delivery. It is located in the front timing chain cover and is perpendicular to the crankshaft target wheel. There is an air gap between the sensor and the target wheel which is not adjustable. The target wheel has three slots 60° apart and is keyed to the crankshaft. As the target wheel rotates, the slots passing by the sensor create a change in the magnetic field of the sensor which results in an induced voltage pulse. One revolution of the crankshaft results in three pulses (3x signal). From these pulses, the VCM is able to determine crankshaft position and engine speed. The VCM then activates the fuel injector and provides spark to the High Voltage Switch. There is a very important relationship between the crankshaft position sensor and the target wheel in that the sensor must be perpendicular to the target wheel and have the precise air gap.

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Fig. High voltage switch distributor



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Fig. Ignition coil-HVS system



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Fig. Camshaft position sensor location-HVS system



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Fig. Crankshaft position sensor-HVS system



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Fig. High Voltage Switch (HVS) system operational schematic

The Ignition Coil Driver (ICD) module is mounted on a bracket next to the ignition coil. The ICD controls the communication between the ignition coil and the VCM. The VCM sends a signal to the ICD commanding it to turn current ON and OFF to the ignition coil at the proper times.

The High Voltage Switch (HVS) is an assembly that looks similar to a distributor. It contains the Camshaft Position (CMP) sensor, cap, rotor and shaft. The HVS shaft is driven by the camshaft and rotates like a distributor providing spark to the correct cylinder using the cap and rotor.

The Camshaft Position (CMP) sensor is located within the HVS. It's operation is very similar to the Crankshaft Position (CKP) sensor, but it provides one pulse per camshaft revolution (1x signal). The VCM uses this signal along with the crankshaft position to determine which cylinder(s) are misfiring. It connects to the VCM through the primary engine harness and provides cylinder identification. The VCM controls the dwell and firing of the ignition coil through an ignition control line to the coil driver.


NOTE
The Camshaft Position sensor does not have any effect on driveability. It's only purpose is to provide the VCM with cylinder identification and other needed information for misfire diagnostic trouble codes.

Hvs Service Precautions


When making compression checks, disconnect the HVS electrical connector to disable the ignition and fuel injection system. Refer to Section 3 for compression check procedures.
 
No periodic lubrication of the high voltage switch is required. Engine oil lubricates the lower bushing and the upper bushing is prelubricated and sealed.
 
There is no manual dwell adjustment.
 
The spark plug wires are made of a material which is very pliable and soft. It is very important to route the spark plug wires correctly to prevent chafing or cutting.
 

Distributor
Installation
Engine Disturbed
  1. Remove the No. 1 cylinder spark plug. Turn the engine using a socket wrench on the large bolt on the front of the crankshaft pulley. Place a finger near the No. 1 spark plug hole and turn the crankshaft until the piston reaches Top Dead Center (TDC). As the engine approaches TDC, you will feel air being expelled by the No. 1 cylinder. If the position is not being met, turn the engine another full turn (360 degree). Once the engine position is correct, install the spark plug.
  2.  
  3. Align the cast arrow in the distributor housing, the driven gear roll pin and the pre-drilled indent hole in the distributor driven gear. If the driven gear is installed correctly, the dimple will be approximately 180° opposite the rotor segment when it is installed in the distributor.
    NOTE
    Installing the distributor 180° out of alignment, or locating the rotor in the wrong holes, may cause a no start condition or can cause premature engine damage and wear.

  4.  
  5. Make sure the rotor is pointing to the cap hold-down mount nearest the flat side of the housing.
  6.  
  7. Using a long screwdriver, align the oil pump driveshaft in the engine in the mating drive tab in the distributor.
  8.  
  9. Install the distributor in the engine. Make sure the spark plug towers are perpendicular to the centerline of the engine.
  10.  
  11. When the distributor is fully seated, the rotor segment should be aligned with the pointer cast in the distributor base. The pointer will have a -6'' cast into it indicating a 6 cylinder engine. If the rotor segment is not within a few degrees of the pointer, the distributor gear may be off a tooth or more. If this is the case repeat the process until the rotor aligns with the pointer.
  12.  
  13. Install the cap and fasten the mounting screws.
  14.  
  15. Tighten the distributor mounting bolt to 18 ft. lbs. (25 Nm).
  16.  
  17. Engage the electrical connections and the spark plug wires.
  18.  

Engine Not Disturbed
  1. If installing a new distributor, place two marks on the new distributor housing in the same position as the marks on the old distributor housing.
  2.  
  3. Align the rotor with the second mark made on the distributor.
  4.  
  5. Install the distributor in the engine making sure that the mounting hole in the distributor hold-down base is aligned over the mounting hole in the intake manifold.
  6.  
  7. As you are installing the distributor, watch the rotor move in a clockwise direction about 42°.
  8.  
  9. Once the distributor is fully seated, the rotor should be aligned with the first mark made on the distributor housing. If the rotor is not aligned with the first mark made on the housing, the distributor and camshaft teeth have meshed one or more teeth out of alignment. If this is the case, remove the distributor and reinstall it so that all the marks are aligned.
  10.  
  11. Install or connect the following:

    Hold-down bolt and tighten the bolt to 18 ft. lbs. (25 Nm)
     
    Distributor cap and engage the electrical connector to the distributor
     
    Spark plug wires and coil leads
     
    Negative battery cable
     

  12.  

Removal
  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Spark plug wires and the coil leads from the distributor
     
    Electrical connector from the distributor
     
    Distributor cap fasteners and the cap
     

  4.  
  5. Using a marker, matchmark the rotor-to-housing and housing-to-intake manifold positions so that they can be matched during installation.

    Distributor hold-down bolt
     
    Distributor from the engine
     

  6.  
  7. As the distributor is being removed from the engine the rotor will move in a counterclockwise direction about 42°. This will appear as slightly more than one clock position.
  8.  
  9. Place a second mark on the distributor to mark the position of the rotor segment. This will help to ensure the correct rotor alignment when installing the distributor.
  10.  

Ignition Coil
Removal & Installation
  1. Disconnect the negative battery cable.
  2.  
  3. Disengage the wiring connectors from the side of the coil.
  4.  
  5. Disconnect the coil wire.
  6.  
  7. Disconnect the nuts holding the coil bracket and coil to the engine bracket or manifold.
  8.  
  9. Drill and punch out the two rivets holding the coil to the bracket then remove the coil bracket and the coil.
    NOTE
    A replacement coil kit comes with two screws to attach the coil to the bracket.



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    Fig. Removing the ignition coil

  10.  

To install:

  1. Connect the coil to the bracket with two screws.
  2.  
  3. Connect the coil and bracket to the engine bracket or manifold with studs and nuts.
  4.  
  5. Tighten the coil hold-down nuts to 20 ft. lbs. (27 Nm).
  6.  
  7. Engage the coil wire, then the wiring connectors at the side of the coil.
  8.  
  9. Connect the negative battery cable.
  10.  

Testing

If the trouble has been narrowed down to one of the components in the ignition system, the following test can help pinpoint the problem. An ohmmeter with both high and low ranges should be used. This test is made with the negative battery cable disconnected.

  1. Disconnect the high voltage switch lead and the wiring from the ignition coil.
  2.  
  3. Set the ohmmeter to the HIGH scale, then connect it to the coil, as shown in Step 1 of the appropriate illustration. The reading should be infinite. If not, verify a proper test connection to be assured of a true test result and if still not infinite, replace the coil.
  4.  
  5. Set the ohmmeter to the LOW scale, then connect it as shown in Step 2 of the appropriate illustration. The reading should be very low or zero. If not, verify a proper test connection and replace the coil.
  6.  
  7. Set the ohmmeter on the HIGH scale, then connect it to the coil as shown in Step 3 of the appropriate illustration. The ohmmeter should NOT read infinite. If it does, verify the connection and replace the coil.
  8.  
  9. Reconnect the high voltage switch lead and wiring to the coil.

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    Fig. Ignition coil testing points

  10.  

Inspection & Testing
High Voltage Switch Inspection
  1. Visually inspect the HVS cap for cracks or tiny holes. Replace the cap if it is damaged or worn.
  2.  
  3. Check the metal terminals in the cap for corrosion. If any corrosion is found, scrape the terminals clean with a suitable scraping tool or replace the cap.
  4.  
  5. Inspect the HVS rotor for wear or burning at the outer terminal. A build-up of carbon on the terminal means the rotor has worn and needs to be replaced.
  6.  
  7. Check HVS shaft for shaft-to-bushing looseness. Place the shaft in the housing. If the shaft wobbles, replace the housing and/or shaft.
  8.  
  9. Visually inspect the HVS housing for cracks or damage.
  10.  

 
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