Test Description
The numbers below refer to the steps in the diagnostic table.
- 2: The chirping noise may not be engine related. This step is to verify that the engine is making the noise. If the engine is not making the noise do not proceed any further in this table.
- 3: The noise may be an internal engine noise. Remove the drive belts and operate the engine for a few seconds, this will verify if the chirping noise is related to the drive belts or not. With the drive belts removed the water pump will not operate and the engine may overheat. Also diagnostic trouble codes (DTCs) may set when the engine is operated with the drive belts removed.
- 4: Inspect the drive belts for signs of pilling. Pilling is the small balls, pills, or strings in the drive belt grooves caused by the accumulation of rubber dust.
- 6: Misalignment of the accessory drive pulleys may be caused from improper mounting or incorrect installation of an accessory drive component, or the pulley may be bent inward or outward from a previous repair. Test for a misaligned accessory drive pulley using a straight edge in the pulley grooves across two or three pulleys. If a misaligned pulley is found, refer to that accessory drive component for the proper removal and installation procedure for that pulley.
- 10: Inspection of the fasteners can eliminate the possibility that a incorrect bolt, nut, spacer, or washer was installed.
- 12: Inspection of the accessory drive pulleys should include inspecting for bends, dents, or other damage to the pulleys that would prevent the drive belts from seating properly in the pulley grooves or on the smooth surface of the pulley when the back side of the drive belt is used to drive the pulley.
- 14: Replacing the drive belts when it is not damaged or there is not excessive pilling will only be a temporary repair.
| Step | Action | Yes | No |
|---|---|---|---|
| NOTE: Refer to Belt Dressing Notice in Cautions and Notices. DEFINITION: The following items are indications of chirping: A high pitched noise that is heard once per revolution of the drive belts or a accessory drive pulley. Chirping may occur on cold damp start-up conditions and will subside once the vehicle reaches normal operating temperature. | |||
| 1 | Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical |
| 2 | Verify that there is a chirping noise. Does the engine make the chirping noise? | Go to Step 3 | Go to Diagnostic Aids |
| 3 | Remove the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Operate the engine for no longer than 30 to 40 seconds. Does the chirping noise still exist? | Go to Engine Noise on Start-Up, but Only Lasting a Few Seconds | Go to Step 4 |
| 4 | Inspect for severe drive belt pilling exceeding 1/3 of the drive belt groove depth. Do the drive belt grooves have pilling? | Go to Step 5 | Go to Step 6 |
| 5 | Clean the accessory drive pulleys with a suitable wire brush. Were the accessory drive pulleys cleaned? | Go to Step 15 | |
| 6 | Inspect for a misaligned accessory drive pulleys. Is there a misaligned accessory drive pulleys? | Go to Step 7 | Go to Step 8 |
| 7 | Replace and/or repair the misaligned accessory drive pulleys. Were the misaligned accessory drive pulleys replaced and/or repaired? | Go to Step 15 | |
| 8 | Inspect for a bent or cracked accessory drive brackets. Did you find any bent or cracked accessory drive brackets? | Go to Step 9 | Go to Step 10 |
| 9 | Replace the bent and/or cracked accessory drive brackets. Was the bent and/or cracked accessory drive brackets replaced? | Go to Step 15 | |
| 10 | Inspect for incorrect, loose and/or missing fasteners. Were there any incorrect, loose, and/or missing fasteners found? | Go to Step 11 | Go to Step 12 |
| 11 | Replace any incorrect and/or missing fasteners. Tighten any loose fasteners. Refer to Fastener Tightening Specifications . Were the fasteners replaced and/or tightened? | Go to Step 15 | |
| 12 | Inspect for a bent accessory drive pulleys. Was a bent accessory drive pulleys found? | Go to Step 13 | Go to Step 14 |
| 13 | Replace the bent accessory drive pulleys. Was the bent accessory drive pulleys replaced? | Go to Step 15 | |
| 14 | Replace the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Was the drive belts replaced? | Go to Step 15 | |
| 15 | Clear any codes. Run the engine in order to verify the repair. Does the chirping noise still exist? | System OK | |
| NOTE |
|---|
| Refer to Belt Dressing Notice in Cautions and Notices. |
Drive Belt Chirping Diagnosis
The numbers below refer to the steps in the diagnostic table.
- 2: The squeal may not be engine related. This step is to verify that the engine is making the noise. If the engine is not making the noise do not proceed further in this table
- 3: The squeal may be an internal engine noise. Remove the drive belts and operate the engine for a few seconds, this will verify if the squealing noise is related to the drive belts or an accessory drive component. With the drive belts removed the water pump will not operate and the engine may overheat. Also diagnostic trouble codes (DTCs) may set when the engine is operated with the drive belts removed.
- 4: This test is to verify that an accessory drive components does not have a seized bearing. With the belts removed, test the bearings in the accessory drive components for smooth operation. Also test the accessory drive components with the engine operating by varying the load on the accessory drive components to verify that the components is operating properly.
- 5: This test is to verify that the drive belts tensioners are not operating properly. If the drive belt tensioners are not operating properly, proper belt tension may not be achieved to keep the drive belts from slipping which could cause a squealing noise.
- 6: This test is to verify that the drive belts is not too long, which would prevent the drive belt tensioners from operating properly. Also if the incorrect length drive belts was installed, it may not be routed correctly and may be turning an accessory drive component in the incorrect direction.
- 7: Misalignment of the accessory drive pulleys may be caused from improper mounting or incorrect installation of a accessory drive component, or the pulley may be bent inward or outward from a previous repair. Test for a misaligned pulley using a straight edge in the pulley grooves across two or three pulleys. If a misaligned pulley is found, refer to that accessory drive component for the proper removal and installation procedure for that pulley.
- 8: Inspect the accessory drive pulleys to verify that they are the correct diameter or width. Using a known good vehicle, compare the accessory drive pulleys.
| Step | Action | Yes | No |
|---|---|---|---|
| NOTE: Refer to Belt Dressing Notice in Cautions and Notices. DEFINITION: The following items are indications of drive belt squeal: A loud screeching noise that is caused by a slipping drive belts (this is unusual for a drive belt with multiple ribs) The squeal occurs when a heavy load is applied to the drive belts, such as an A/C compressor engagement, snapping the throttle, slipping on a seized pulley, or a faulty accessory drive component. | |||
| 1 | Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical |
| 2 | Verify that there is a squealing noise. Does the engine make the squeal noise? | Go to Step 3 | Go to Diagnostic Aids |
| 3 | Remove the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Operate the engine for no longer than 30 to 40 seconds. Does the squealing noise still exist? | Go to Engine Noise on Start-Up, but Only Lasting a Few Seconds | Go to Step 4 |
| 4 | Inspect for a seized accessory drive component bearing or a faulty accessory drive component. Did you find and correct the condition? | Go to Step 9 | Go to Step 5 |
| 5 | Inspect the drive belt tensioner for proper operation. Refer to Drive Belt Tensioner Diagnosis . Did you find and correct the condition? | Go to Step 9 | Go to Step 6 |
| 6 | Check for the correct length drive belts. Did you find and correct the condition? | Go to Step 9 | Go to Step 7 |
| 7 | Inspect for a misaligned pulley. Did you find and correct the condition? | Go to Step 9 | Go to Step 8 |
| 8 | Inspect for an incorrect size pulley. Did you find and correct the condition? | Go to Step 9 | |
| 9 | Install the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Clear any codes. Run the engine in order to verify the repair. Does the squealing noise still exist? | System OK | |
| NOTE |
|---|
| Refer to Belt Dressing Notice in Cautions and Notices. |
Drive Belt Squeal Diagnosis
The numbers below refer to the steps in the diagnostic table.
- 3: This test is to verify that the whine is being caused by the accessory drive components. Remove the drive belts and operate the engine for a few seconds, this will verify if the whining noise is related to the accessory drive component. With the drive belts removed the water pump will not operate and the engine may overheat. Also diagnostic trouble codes (DTCs) may set when the engine is operated with the drive belts removed.
- 4: This inspection should include checking the drive belt tensioner and the drive belt idler pulley bearings. The drive belts may have to be installed and the accessory drive components operated separately by varying their loads. Refer to the suspected accessory drive component for the proper removal and installation procedure.
| Step | Action | Yes | No |
|---|---|---|---|
| NOTE: Refer to Belt Dressing Notice in Cautions and Notices. DEFINITION: A high pitched continuous noise that may be caused by an accessory drive component failed bearing. | |||
| 1 | Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical |
| 2 | Verify that there is a whining noise. Does the engine make the whining noise? | Go to Step 3 | Go to Diagnostic Aids |
| 3 | Remove the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Operate the engine for no longer than 30 to 40 seconds. Does the whining noise still exist? | Go to Engine Noise on Start-Up, but Only Lasting a Few Seconds | Go to Step 4 |
| 4 | Inspect for a failed accessory drive component bearing. Install the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Did you find and correct the condition? | Go to Step 5 | |
| 5 | Clear any codes. Run the engine in order to verify the repair. Does the whining still exist? | System OK | |
| NOTE |
|---|
| Refer to Belt Dressing Notice in Cautions and Notices. |
Drive Belt Whine Diagnosis
The numbers below refer to the steps in the diagnostic table.
- 2: This test is to verify that the symptom is present during diagnosing. Other vehicle components may cause a similar symptom.
- 3: This test is to verify that the drive belts is causing the rumbling. Rumbling may be confused with an internal engine noise due to the similarity in the description. Remove only one drive belt at a time if the vehicle has multiple drive belts. Operate the engine for a few seconds, this will verify if the rumbling noise is related to the drive belts or not. With the drive belts removed the water pump will not operate and the engine may overheat. Also diagnostic trouble codes (DTCs) may set when the engine is operated with the drive belts removed.
- 4: Inspect the drive belts to ensure that the drive belts is not the cause of the noise. Small cracks across the ribs of the drive belts will not cause the noise. Belt separation is identified by the plies of the belt separating, this may be seen at the edge of the belt or felt as a lump in the belt.
- 5: Small amounts of pilling is a normal condition and acceptable. When the pilling is severe the drive belts does not have a smooth surface for proper operation.
| Step | Action | Yes | No |
|---|---|---|---|
| NOTE: Refer to Belt Dressing Notice in Cautions and Notices. DEFINITION: A low pitch tapping, knocking, or thumping noise heard at or just above idle. Heard once per revolution of the drive belts or pulleys. Rumbling may be caused from: Pilling, the accumulation of rubber dust that forms small balls (pills) or strings in the drive belts pulley groove The separation of the drive belts A damaged drive belts | |||
| 1 | Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical |
| 2 | Verify that there is a rumbling noise. Does the engine make the rumbling noise? | Go to Step 3 | Go to Diagnostic Aids |
| 3 | Remove the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Operate the engine for no longer than 30 to 40 seconds. Does the rumbling noise still exist? | Go to Engine Noise on Start-Up, but Only Lasting a Few Seconds | Go to Step 4 |
| 4 | Inspect the drive belts for damage, separation, or sections of missing ribs. Were any of these conditions found? | Go to Step 7 | Go to Step 5 |
| 5 | Inspect for severe pilling of more than 1/3 of the drive belt groove depth. Do the drive belt grooves have pilling? | Go to Step 6 | Go to Step 7 |
| 6 | Clean the drive belt pulleys using a suitable wire brush. Reinstall the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Did you complete the repair? | Go to Step 8 | |
| 7 | Install a new drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Did you complete the replacement? | Go to Step 8 | |
| 8 | Clear any codes. Run the engine in order to verify the repair. Does the rumbling noise still exist? | System OK | |
| NOTE |
|---|
| Refer to Belt Dressing Notice in Cautions and Notices. |
Drive Belt Rumbling Diagnosis
The numbers below refer to the steps in the diagnostic table.
- 2: This test is to verify that the vibration is present during diagnosing. Other vehicle components may cause a similar symptom such as the exhaust system, or the drivetrain.
- 3: This test is to verify that the drive belts or accessory drive components may be causing the vibration. Remove the drive belts and operate the engine for a few seconds, this will verify if the vibration is related to the drive belts or not. With the drive belts removed the water pump will not operate and the engine may overheat. Also diagnostic trouble codes (DTCs) may set when the engine is operated with the drive belts removed.
- 4: The drive belts may cause a vibration. While the drive belts is removed this is the best time to inspect the condition of the drive belts.
- 6: Inspection of the fasteners can eliminate the possibility that a incorrect bolt, nut, spacer, or washer was installed.
- 8: This step should only be performed if the fan is driven by the drive belt. Inspect the engine cooling fan for bent, twisted, loose, or cracked blades. Inspect the fan clutch for smooth operation. Inspect for a bent fan shaft or bent mounting flange.
- 9: Inspect the water pump drive shaft for being bent. Also inspect the water pump bearings for smooth operation and excessive play. Compare the water pump with a known, good water pump.
- 10: Accessory drive component brackets that are bent, cracked, or loose may put an extra strain on that accessory drive component causing it to vibrate.
| Step | Action | Yes | No |
|---|---|---|---|
| NOTE: Refer to Belt Dressing Notice in Cautions and Notices. DEFINITION: The following items are indications of drive belt vibration: The vibration is engine-speed related. The vibration may be sensitive to accessory load. | |||
| 1 | Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical |
| 2 | Verify that the vibration is engine related. Does the engine make the vibration? | Go to Step 3 | Go to Diagnostic Aids |
| 3 | Remove the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Operate the engine for no longer than 30 to 40 seconds. Does the engine still make the vibration? | Go to Diagnostic Starting Point - Vibration Diagnosis and Correction in Vibration Diagnosis and Correction | Go to Step 4 |
| 4 | Inspect the drive belts for wear, damage, debris build-up and missing drive belt ribs. Were any of these conditions found? | Go to Step 5 | Go to Step 6 |
| 5 | Install a new drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Did you complete the replacement? | Go to Step 11 | |
| 6 | Inspect for incorrect, loose, or missing fasteners. Were any of these conditions found? | Go to Step 7 | Go to Step 8 |
| 7 | Replace any incorrect and/or missing fastener. Tighten any loose fasteners. Refer to Fastener Tightening Specifications . Were the fasteners replaced and/or tightened? | Go to Step 11 | |
| 8 | Inspect for damaged fan blades or a bent fan clutch shaft. Did you find and correct the condition? | Go to Step 11 | Go to Step 9 |
| 9 | Inspect for a bent water pump drive shaft. Did you find and correct the condition? | Go to Step 11 | Go to Step 10 |
| 10 | Inspect for a bent or cracked accessory drive brackets. Did you find and correct the condition? | Go to Step 11 | |
| 11 | Clear any codes. Run the engine in order to verify the repair. Does the vibration still exist? | System OK | |
| NOTE |
|---|
| Refer to Belt Dressing Notice in Cautions and Notices. |
Drive Belt Vibration Diagnosis
The numbers below refer to the steps in the diagnostic table.
- 2: This inspection is to verify the condition of the drive belts. Damage may have occurred to the drive belts when the drive belts fell off the pulley. Inspect the drive belts for cuts, tears, sections of ribs missing, or damaged belt plies.
- 4: Misalignment of the accessory drive pulleys may be caused from improper mounting or incorrect installation of a accessory drive component, or the pulley may be bent inward or outward from a previous repair. Test for a misaligned pulley using a straight edge in the pulley grooves across two or three pulleys. If a misaligned pulley is found, refer to that accessory drive component for the proper removal and installation procedure of that pulley.
- 5: Inspection of the accessory drive pulleys should include inspecting for bends, dents, or other damage that would prevent the drive belt from seating properly in the pulley grooves or on the smooth surface of a pulley when the back side of the drive belts is used to drive the pulley.
- 6: Accessory drive component brackets that are bent or cracked will also cause the drive belts to fall off.
- 7: Inspection of the fasteners can eliminate the possibility that a incorrect bolt, nut, spacer, or washer was installed. Missing, loose, or incorrect fasteners may cause pulley misalignment from the accessory drive brackets moving under load. Over tightening the fasteners may cause misalignment of the accessory component brackets.
| Step | Action | Yes | No |
|---|---|---|---|
| NOTE: Refer to Belt Dressing Notice in Cautions and Notices. DEFINITION: The drive belts falls off the pulleys or may not ride correctly on the pulleys. | |||
| 1 | Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical |
| 2 | Inspect for a damaged drive belts. Was a damaged drive belts found? | Go to Step 3 | Go to Step 4 |
| 3 | Install a new drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Does the drive belts continue to fall off? | Go to Step 4 | System OK |
| 4 | Inspect for a misaligned accessory drive pulleys. Did you find and correct the condition? | Go to Step 12 | Go to Step 5 |
| 5 | Inspect for a bent or dented accessory drive pulleys. Did you find and correct the condition? | Go to Step 12 | Go to Step 6 |
| 6 | Inspect for a bent or a cracked accessory drive brackets. Did you find and correct the condition? | Go to Step 12 | Go to Step 7 |
| 7 | Inspect for incorrect, loose and/or missing fasteners. Were there any incorrect, loose and/or missing fasteners? | Go to Step 8 | Go to Step 9 |
| 8 | Replace any incorrect and/or missing fasteners. Tighten any loose fasteners. Refer to Fastener Tightening Specifications . Does the drive belt continue to fall off? | Go to Step 9 | System OK |
| 9 | Test the drive belt tensioner for correct operation. Refer to Drive Belt Tensioner Diagnosis . Does the drive belt tensioner operate correctly? | Go to Step 11 | Go to Step 10 |
| 10 | Replace the drive belt tensioner. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Does the drive belt continue to fall off? | Go to Step 11 | System OK |
| 11 | Inspect for a failed drive belt idler and/or tensioner pulley bearing. Did you find and repair the condition? | Go to Step 12 | |
| 12 | Run the engine in order to verify the repair. Does the drive belt still fall off? | System OK | |
| NOTE |
|---|
| Refer to Belt Dressing Notice in Cautions and Notices. |
Drive Belt Falls Off Diagnosis
The numbers below refer to the steps in the diagnostic table.
- 2: This inspection is to verify that the drive belts is correctly installed on all of the accessory drive pulleys. Wear on the drive belts may be caused by incorrect positioning of the drive belts by one or more grooves on a pulley.
- 3: The installation of a drive belts that is too wide or too narrow will cause wear on the drive belts. The drive belts ribs should match all of the grooves on the pulleys.
- 4: This inspection is to verify that the drive belts is not contacting any part of the engine or body while the engine is operating. Provide sufficient clearance when the accessory drive components load varies. The drive belts should not come in contact with an engine or a body component when snapping the throttle.
| Step | Action | Yes | No |
|---|---|---|---|
| NOTE: Refer to Belt Dressing Notice in Cautions and Notices. DEFINITION: Wear at the outside ribs of the drive belts due to incorrect installation of the drive belts. | |||
| 1 | Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical |
| 2 | Inspect the drive belts for proper installation. Is the drive belts installed properly? | Go to Step 5 | Go to Step 3 |
| 3 | Inspect for the correct drive belts. Is the correct drive belt installed? | Go to Step 5 | Go to Step 4 |
| 4 | Inspect the drive belts for signs of rubbing against a bracket, hose, or wiring harness. Was the drive belts rubbing against anything? | Go to Step 5 | Go to Diagnostic Aids |
| 5 | Replace the drive belts. Refer to Drive Belt Replacement - Accessory or to Drive Belt Replacement - Air Conditioning . Did you complete the replacement? | Go to Step 6 | |
| 6 | Run the engine in order to verify the repair. Is there still excessive drive belt wear? | System OK | |
| NOTE |
|---|
| Refer to Belt Dressing Notice in Cautions and Notices. |
Drive Belt Excessive Wear Diagnosis
Crankcase Ventilation System Description
A closed crankcase ventilation system provides a more complete scavenging of crankcase vapors. Fresh air from the throttle body is supplied to the crankcase, mixed with blow-by gases, and then passed through a crankcase ventilation pipe/passage into the intake manifold.
Results of Incorrect Operation
A plugged positive crankcase ventilation (PCV) pipe/passage way may cause any of the following conditions
- Rough idle
- Stalling or slow idle speed
- Oil leaks
- Sludge in engine
Drive Belt System Description
The drive belt system consists of the following components
- The drive belt
- The drive belt tensioner
- The drive belt idler pulley
- The crankshaft balancer pulley
- The accessory drive component mounting brackets
- The accessory drive components The power steering pump, if belt driven The generator The A/C compressor, if equipped The engine cooling fan, if belt driven The water pump, if belt driven The vacuum pump, if equipped The air compressor, if equipped
The drive belt system may use 1 belt or 2 belts. The drive belt is thin so that it can bend backwards and has several ribs to match the grooves in the pulleys. There also may be a V-belt style belt used to drive certain accessory drive components. The drive belts are made of different types of rubbers - chloroprene or EPDM - and have different layers or plies containing either fiber cloth or cords for reinforcement.
Both sides of the drive belt may be used to drive the different accessory drive components. When the back side of the drive belt is used to drive a pulley, the pulley is smooth.
The drive belt is pulled by the crankshaft balancer pulley across the accessory drive component pulleys. The spring loaded drive belt tensioner keeps constant tension on the drive belt to prevent the drive belt from slipping. The drive belt tensioner arm will move when loads are applied to the drive belt by the accessory drive components and the crankshaft.
The drive belt system may have an idler pulley, which is used to add wrap to the adjacent pulleys. Some systems use an idler pulley in place of an accessory drive component when the vehicle is not equipped with the accessory.
Scheme 67
The 5.3 liter V8 engine is identified as RPO LH6 VIN M.
System Operation
General Motors Displacement on Demand® (DOD) engine control system has the ability, under certain light load driving conditions, to provide maximum fuel economy by deactivating 4 of the engines 8 cylinders. The engine will normally operate on 8 cylinders in V8 mode during, starting, idling, and medium or heavy throttle conditions. When commanded ON, the engine control module (ECM) will direct the DOD system and deactivate cylinders 1 and 7 on the left bank and cylinders 4 and 6 on the right bank, forcing V4 mode. Refer to Lubrication Description (Main Pressure Below 55 psi - DOD Off) or Lubrication Description (Main Pressure Above 55 psi - DOD Off) or Lubrication Description (Main Pressure Below 55 psi - DOD On) or Lubrication Description (Main Pressure Above 55 psi - DOD On) and Displacement on Demand (DOD) System Description in Engine Controls.
Scheme 68
The valve lifter oil manifold (VLOM) assembly (1) is bolted to the top of the engine block beneath the intake manifold assembly. The oil manifold consists of 4 electrically operated and normally-closed solenoids (2). Each solenoid directs the flow of pressurized engine oil to the DOD intake and exhaust valve lifters (5). The oil pressure relief valve (6), located in the oil pan, regulates engine oil pressure to the lubrication system and the oil manifold.
When enabling conditions are met for DOD operation, the ECM will ground each solenoid control circuit in firing order sequence, allowing current to flow through the solenoid windings. With the windings energized, the solenoid valves open and direct pressurized engine oil through the VLOM into 8 vertical passages in the engine block lifter valley. The 8 vertical passages, 2 per cylinder, direct pressurized oil to the valve lifter bores of the cylinders to be deactivated. When vehicle operating conditions require a return to V8 mode, the ECM will turn OFF the ground circuit for the solenoids, allowing the solenoid valves to close. When the solenoid valves are closed, remaining oil pressure is exhausted through the bleed passages of the VLOM into the engine block lifter valley. The housing of the oil manifold incorporates several oil bleed passages that continually purge trapped air from the manifold and engine block.
To help control contamination within the DOD hydraulic system, a small replaceable oil filter (4) is located in the VLOM oil inlet passage. The oil pressure sensor (3) monitors engine oil pressure and provides information to the ECM.
Scheme 69
When operating in V8 mode, the DOD valve lifters function similar to the non-DOD valve lifters. The DOD oil manifold solenoids are in the closed position, with no pressurized oil directed to the valve lifters. The pushrod (1) travels upward and downward to actuate the rocker arm and valve. The spring loaded locking pins (5) of the lifter are extended outward and mechanically lock the pin housing (4) to the outer body of the valve lifter (3).
When the DOD system is commanded ON, the ECM will direct the solenoids of the oil manifold to open and direct pressurized oil to the valve lifters. Oil travels through the VLOM and engine block oil galleries and enters the inlet port (6) of the valve lifter.
When operating in V4 mode, pressurized oil forces the locking pins (11) inward. The pushrod (7) remains in a constant position and does not travel upward and downward. The outer body of the lifter (9) moves upward and downward independently from the pin housing (10). The valve lifter spring (8) retains tension on the valve train components to eliminate valve train noise.
When the DOD system is commanded OFF, the ECM directs the solenoids of the oil manifold to close, stopping the flow of pressurized oil to the valve lifters. The oil pressure within the lifter will decrease and the locking pins will move outward to mechanically lock the pin housing and outer body.
Scheme 70
The DOD engine block incorporates additional features to support DOD system operation. Engine oil pressure is routed to the VLOM assembly from an oil gallery (2) in the rear of the cylinder block. Cylinders 1, 4, 6, and 7 each have 2 vertical, cast-in-block oil passages (1). The vertical oil passages permit oil flow from the manifold assembly to the valve lifter bores.