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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 27664
Experience:  GM Grand Master Technician 2007. 11 years experience.
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I have a 2008 chevy silverado z71, 5.3l engine. It has been

Resolved Question:

I have a 2008 chevy silverado z71, 5.3l engine. It has been running fine but there are two things concerning me. 1) at about 1200 rpms there is a rattle/vibration noise comming from underneath the truck. 2) More importantly, this morning when i cranked up the truck it was clicking loudly, and when i reved the engine the clicking noise sped up with the reving of the engine.
Submitted: 4 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 4 years ago.

Welcome. Does your truck have the Active fuel management?

Customer: replied 4 years ago.
To be quite honest, I really have no idea. How would I be able to find out if it does or not? I've never really seen anything about that but that doesnt mean it doesnt have it.
Expert:  GM Tech (Cam) replied 4 years ago.
Do you ever notice a V4 Or V* mode in the dash?
Customer: replied 4 years ago.
Oh, yes it does switch from v4 mode to v8 mode, it has stopped clicking now. I just went outside to crank it and it is no longr doing it.
Expert:  GM Tech (Cam) replied 4 years ago.
OK, these engines are common for the special lifters that disable the cylinder for failing. I suggest you go to your dealer and talk to them. THis should easily be under the power train warranty.
Customer: replied 4 years ago.
So< i should still be concerned about the clicking even though it has stopped? there is a potential problem going on that I should have checked out?
Expert:  GM Tech (Cam) replied 4 years ago.
YEs, IT will likely start again. If this is the lifters, they will replace all the lifters and the oil pump. GM has a bulletin about this.
Customer: replied 4 years ago.
Ok, so i can just go to the gm website to learn more about this?
Expert:  GM Tech (Cam) replied 4 years ago.

Bulletins are not as easily found so I will post it here.

2008 Chevrolet Silverado - 4WD | Sierra, Silverado (VIN C/K) Service Manual | Document ID:(NNN) NNN-NNNN


#PIP4568F: Tick Noise And/Or Misfires On AFM Cylinders 1 4 6 And/Or 7 - keywords possible - (Dec 14, 2009)

Subject:Tick Noise and/or Misfires on AFM Cylinders 1, 4, 6, and/or 7

Models:2008-2009 Buick LaCrosse, Allure (Canada Only)
2007-2009 Cadillac Escalade
2007-2009 Chevrolet Avalanche
2007-2009 Chevrolet Silverado, Suburban, Tahoe
2006-2009 Chevrolet Trailblazer
2006-2009 Chevrolet Impala SS
2006-2007 Chevrolet Monte Carlo SS
2006-2009 GMC Envoy
2007-2009 GMC Sierra, Yukon
2008-2009 Pontiac G8
2005-2008 Pontiac Grand Prix GXP
2006-2009 Saab 97x
with a V8 Engine and AFM (Active Fuel Management)
(RPO Codes L76, LC9, LFA, LH6, LMG, LS4, and LY5)

 


This PI was superseded to update Recommendation/Instructions. Please discard PIP4568E.


 

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

Condition/Concern:

Some customers may comment on an SES light, engine misfire on cylinder 1, 4, 6, or 7, and/or tick noise. This may be the result of an AFM lifter that unlocks as soon as the engine is started or one that is mechanically collapsed/stuck all of the time.

If an AFM lifter unlocks as soon as the engine is started, low compression will be experienced on that cylinder during an AFM compression test, along with a SES light and DTC P0300 with engine misfires on the related cylinder but it is unlikely that any noise will be experienced.

If an AFM lifter is mechanically collapsed/stuck, low compression will be experienced on that cylinder during an AFM compression test, along with a consistent valve train tick noise, SES light, and DTC P0300 will be experienced with engine misfires on the related cylinder.

Recommendation/Instructions:

If this concern is experienced, perform SI diagnosis. If SI does not isolate the cause of this concern, perform the following tests:

Cylinder Deactivation (Active Fuel Management) System Compression Test in SI. If the running compression of the misfiring cylinder stays below 25 PSI regardless of the AFM solenoid being commanded on or off, an AFM lifter is mechanically collapsed/stuck or unlocking as soon as the engine is started.

Cylinder Deactivation (Active Fuel Management) Valve Lifter Oil Manifold Diagnosis and Testing in SI. If the test above isolated a possible AFM lifter concern, it will lead to this test, which tests the VLOM (Valve Lifter Oil Manifold) for proper operation. SI states a limited amount of air will leak from the bleed holes and outlet ports even when the solenoids are off, compare the amount of leakage to verify all 4 solenoids are operating the same. If it isolates a concern with the VLOM, replace it and re-evaluate the concern.

In addition to the SI diagnostic test above, the AFM lifters can also be monitored for proper operation by carefully inspecting the cylinder 1, 4, 6, and 7 rockers and valves while cranking or running the engine with the valve covers removed.

If the tests above isolate an AFM lifter concern, inspect the related lifter to determine if it is physically collapsed/stuck all of the time.

If a collapsed/stuck lifter is found, it may be the result of the lifter ingesting air through the oil pump and/or pick up tube oring, which can damage the lifters. If a collapsed lifter is found, follow SI repair procedures to replace the oil pump, pick up tube o-ring, and all AFM lifters.

If a collapsed/stuck lifter is not found but the related lifter(s) is unlocking upon start up causing low running compression and/or no rocker/valve movement, there may be a concern with the related lifter and VLOM. If this concern is encountered, replace the VLOM and all AFM lifters.

GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 27664
Experience: GM Grand Master Technician 2007. 11 years experience.
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