Subject:Short Duration Cold Start Lifter Tick Noise


Models:2007-2008 Chevrolet Avalanche, Silverado, Suburban, Tahoe2007-2008 GMC, Sierra, Yukon2007-2008 Chevrolet Impala2007 Chevrolet Monte CarloEquipped with the 5.3 or 6.0 Active Fuel Management engines


The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

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Condition/Concern:
A customer may comment on a cold start engine tick noise. The noise explained may be an extended duration noise related to AFM (Active Fuel Management) valve lifters. The noise may repeat on subsequent cold starts. Noise will be camshaft speed and may last over 1 minute. Noise will only occur after a cold soak that is greater than four hours in duration.

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Recommendation/Instructions:
Complete the current SI diagnostic for any symptom or DTCs found. If an extended duration lifter tick noise has been verified (usually greater than 1 minute), and the noise is considered excessive and repeatable, lifter replacement may be required. To repair this concern all lifters should be replaced with lifters obtained through GMSPO. There is no special part number necessary.

Note: The 6.0L engine, RPO code LFA has been built with updated lifters since 1-28-2008. 6.0 LFA engines built prior to 1-28-2008 may need the lifters replaced if the customer concern is as described in this PI.

Note: If a cold start lifter tick noise has been verified on any other 5.3L or 6.0L AFM engine, lifter replacement may be necessary. These engines (L76 LC9 LH6 LMG LS4 LY5) do not have a build date released for updated lifters.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.


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Excessive Oil Consumption And/Or Blue Exhaust Smoke - (Apr 28, 2010)

Subject: Excessive Oil Consumption and/or Blue Exhaust Smoke

Models: 2007 Buick Rainier

2007-2008 Chevrolet Avalanche, Silverado, Suburban, Tahoe, Trail Blazer

2007-2008 GMC Envoy, Sierra, Yukon

2007-2008 Saab 97x

with AFM (Active Fuel Management) 5.3L Engine (RPOs LC9, LH6, LMG, LY5)

This PI was superseded to suggest only lifter replacement on the left bank of the engine when there is oil in the intake instead of replacing all 16 lifters. Please discard PIP4574H.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Some customers may complain that their vehicle has been using approximately 1 quart of oil every 500-1,000 miles. In most cases, the customer will advise that this did not start until the engine accumulated approximately 30,000 miles or more. In some cases, the customer may note that this is more apparent when driving at highway speed. In rare instances, a SES light and engine misfire may be encountered with a P0300 DTC.

Upon inspection, an oil fouled spark plug(s) may be noted. In most cases, static compression and cylinder leakage testing will appear normal. Excessive oil may or may not be found in the intake manifold.

In most cases, this is the result of stuck oil control rings. Generally, the stuck oil control rings are the result of excessive oil on the cylinder walls. The excessive oil can come from the PCV system and/or the AFM pressure relief valve in the oil pan.

Visually inspect the entire engine and the underside of the vehicle for any evidence of oil leaks and repair them as necessary.
Inspect the fresh air hose/pipe that is attached to the RF (passenger side) valve cover and all related connections for restrictions, such as plastic casting flash or a pinched hose, and repair as necessary. A restriction in this area may cause excessive crankcase vacuum and oil consumption through the PCV vacuum tube.
If the truck has an engine misfire and a spark plug that is obviously oil fouled, skip to step 4.
If not, perform an oil consumption test as outlined in the latest version of oil consumption of 01-06-01-011 to verify the concern before proceeding to step 4. Allow the vehicle to sit on a level surface with the engine off for at least 10 minutes to allow the entire engine to drain back to the oil pan before checking the engine oil level and adding oil. Compare the oil consumption test results to one of the scenarios below to determine further direction:

• If oil consumption is Less than 1 quart of oil every 2,000 miles and no low oil light has been experienced, no repairs should be performed as this should be considered acceptable oil consumption as outlined in the latest version of 01-06-01-011.

• If oil consumption is Less than 1 quart of oil every 2,000 miles but the customer has experienced a low oil light, refer to the latest version of PIP3959 for a potential low oil light sensor concern.

• If the dealership verifies that oil consumption is More than 1 quart every 2,000 miles, perform the steps below as necessary:

Determine if the engine has been ingesting oil through the PCV system by removing the intake manifold and measuring how much oil can be poured out of the throttle body opening with the throttle body removed. It is normal to get a couple of teaspoons of oil out of the intake. If the engine has been ingesting oil through the PCV system, several ounces of oil will be measured, many times as much as a 1/4-1/2 quart. If the engine has NOT been ingesting oil through the PCV system, go to step 5. If the engine HAS been ingesting oil through the PCV system, go to step 6 to inspect the PCV baffle.
If the engine has NOT been ingesting oil through the PCV system, select one of the following options (5a or 5b) on a case by case basis. If necessary, review the following options with your FOM (Fixed Operations Manager - GM Rep.) if their feedback is needed for customer satisfaction, etc.:
• 5a. If the customer has not experienced a SES light and engine misfire due to an oil fouled spark plug, you can explain that a permanent repair procedure is being developed to address this and that it should be available sometime this summer. The oil consumption is most likely the result of AFM pressure relief valve oil accumulating on the bottom of the cylinders, eventually leading to the stuck oil control rings and increased oil consumption. An AFM pressure relief valve shield and procedures to unstick the rings and install the shield are being developed to address this. These parts and procedures should be available sometime this summer. As soon as they are available, this PI will be updated with more details.

• 5b. If you decide to pursue repairs, inspect for stuck oil control rings. If stuck oil control rings are found, replace all 8 pistons and all 8 piston ring sets. Due to the great variation between equipment, machine shops, and technicians performing these repairs, we DO NOT recommend honing or deglazing the cylinder walls though. This is just because it is generally unnecessary and can induce unnecessary cylinder wall and/or piston ring damage if it is done incorrectly or not cleaned thoroughly. The cylinder walls just need to be cleaned thoroughly with brake cleaner before the new piston and ring sets are installed. As mentioned above, the oil consumption is most likely the result of AFM pressure relief valve oil accumulating on the bottom of the cylinders, eventually leading to the stuck oil control rings and increased oil consumption. An AFM pressure relief valve shield and procedures to unstick the rings and install the shield are being developed to address this. These parts and procedures should be available sometime this summer. As soon as they are available, this PI will be updated with more details.

If the engine HAS been ingesting oil through the PCV system, inspect the PCV baffle as outlined below in step 6:
• 6a. Remove the LH (driver's side) valve cover and inspect the PCV baffle drain holes shown below to see if they are plugged with hardened oil deposits. If they are plugged, replace the valve cover, ensure that the customer is changing their oil according to the maintenance schedule in their owner's manual, and re-evaluate the concern. Generally, this would not be a concern until several thousand miles have accumulated.


• 6b. With the LH (driver's side) valve cover removed, inspect the PCV baffle to ensure that it is properly sealed to the valve cover by flipping it over and adding a little oil to the corner of the valve cover as shown below. The oil should stay in place as shown on the 2 outer valve covers below. If the oil drains into the PCV baffle as pointed out on the middle valve cover below, replace the valve cover. Generally, if this is the cause of the concern, it would have been present early in the life of the vehicle or shortly after valve cover replacement.


Important: If Step 6a or 6b led to valve cover replacement, perform Step 6b again on the replacement valve cover before installing it. If step 6 does not isolate a PCV baffle concern, go to step 7.


If the engine HAS been ingesting oil through the PCV system but the valve cover passed the tests outlined above in steps 6a and 6b, the engine may have an over-aggressive lifter that is causing the oil ingestion through the PCV system. Sometimes the lifter may be doing this intermittently so it is not always possible to isolate one by inspecting the lifter flow with the driver's valve cover removed. Additionally, the oil control rings may be stuck and contributing to the overall oil consumption concern as well. As a result, select one of the following repair options (7a or 7b) on a case by case basis. If necessary, review the following repair options with your FOM (Fixed Operations Manager - GM Rep.) to get their feedback for customer satisfaction, etc.:
• 7a. Replace all 8 of the left/driver bank lifters due to the oil in the intake and re-evaluate the oil consumption concern. The right/passenger side lifters should not cause oil in the intake so there is no need to replace them. If the vehicle returns with excessive oil consumption but is no longer ingesting oil through the PCV system, it most likely has stuck oil control rings and you would have to start at step 5 again.

• 7b. Replace all 8 of the left/driver bank lifters due to the oil in the intake but also remove all 8 pistons to inspect for stuck oil control rings since the heads are going to be off anyhow. There is a good chance the engine could also have stuck oil control rings that are contributing to the oil consumption as well. If stuck oil control rings are found, also replace all 8 pistons and all 8 piston ring sets at the same time as the lifters. Due to the great variation between equipment, machine shops, and technicians performing these repairs, we DO NOT recommend honing or deglazing the cylinder walls though. This is just because it is generally unnecessary and can induce unnecessary cylinder wall and/or piston ring damage if it is done incorrectly or not cleaned thoroughly. The cylinder walls just need to be cleaned thoroughly with brake cleaner before the new piston and ring sets are installed. As mentioned above, the oil consumption is most likely the result of AFM pressure relief valve oil accumulating on the bottom of the cylinders, eventually leading to the stuck oil control rings and increased oil consumption. An AFM pressure relief valve shield and procedures to unstick the rings and install the shield are being developed to address this. These parts and procedures should be available sometime this summer. As soon as they are available, this PI will be updated with more details.