Vibration In 4 Cyl. Mode

[dave_benn]

When my truck kicks into 4 cyl mode it vibrates so bad the change in my ashtray jingles. It does it anytime 4 cyl mode is activated. 30 mph, 65 mph, ect. Anyone else experiencing this? Also when my truck goes back to V8 mode (cruise is on) the RPM's jump 200 and back down to where they were, just a little flair. Truck has 7500 miles on it and already had the lifters replaced, very disappointed in this AFM junk.

[nickvrebel]

there is a problem, that is not normal. my truck switches from 4 to 8 seamlessly, if anything there is a slight "tug" when returning to 8 cyl, but I can't see it in the tach.

[dave_benn]

I can feel it when it hits 8 cyl mode too. When it drops into 4 cyl. mode its like it throws a parachute out the back. I have a K&N filter and MBRP exhaust, but that should't affect anything, should it?

[jdubub]

The filter and exhaust shouldnt play a role in it i wouldnt think. when mine drops to 4 i can only hear it in exhaust tone but when it kicks back in 8 it feeks like a slight kick but my tach doesnt move. I just think of it as well no shit wouldnt a big v8 have a slight kick over a 4

[MS3DALE]

Service Information 2010 GMC Truck Sierra - 4WD | Sierra, Silverado VIN C/K Service Manual | Document ID: 2405891

--------------------------------------------------------------------------------

 

#06-06-05-001D: Information on Change in Exhaust Tone or Sound for Active Fuel Management (AFM) System Equipped Engines in Three or Four Cylinder Mode - (Feb 23, 2010)

 

 

Subject: Information on Change in Exhaust Tone or Sound For Active Fuel Management (AFM) System Equipped Engines in Three or Four Cylinder Mode

 

 

Models: 2007 Buick Rainier

 

2007-2009 Buick Allure (Canada Only), LaCrosse

 

2007 Chevrolet Monte Carlo

 

2007-2009 Chevrolet TrailBlazer

 

2007-2010 Chevrolet Avalanche, Impala, Silverado, Suburban, Tahoe

 

2010 Chevrolet Camaro

 

2007-2009 GMC Envoy Denali

 

2007-2010 GMC Sierra, Yukon, Yukon XL, Yukon Denali

 

2007-2009 Saab 9-7X

 

with Active Fuel Management System Vortec® GEN IV 5.3L, 6.0L or 6.2L V8 Engine RPOs LMG, LC9, LY5, LH6, L76, L77, LFA, LZ1, LS4, L94, L99 or 3.9L V6 Engine RPOs LZ8, LZG

 

 

Some customers may comment on a change in the exhaust note or tone when an Active Fuel Management System equipped engine is in 3 or 4 cylinder mode. Some drivers may also notice a very slight vibration in either the accelerator pedal, floor pan and/or the steering wheel. This is a normal condition for Active Fuel Management System equipped vehicles and no repairs should be attempted.

 

Customer Information on Active Fuel Management

When the Active Fuel Management System is enabled, physical changes take place within the engine that allow it to run as a 3 or 4 cylinder motor with accompanying additional fuel savings. The change in exhaust tone is expected as all sound from the exhaust is the result of combustion in the engine. The ability to perceive these changes in sound are kept to very minimal levels as the Active Fuel Management System is only activated during steady state/near steady state driving or during coast down. In both of these situations, the load on the engine is minimal and general exhaust volume (sound) is low.

 

You may give a copy of this bulletin to your customer.

 

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.

 

© 2010 General Motors. All rights reserved.

[jdubub]

MS3DALE-RICH...... you are full of all sorts of useful info!

[MS3DALE]

Sometimes I'm full of "useless" information too!

[dave_benn]

Thanks for the info.

[dave_benn]

MSDALE3: what about the rpm jump, is that also normal or should i bring the truck in to have it looked at?

[ybsane]

MSDALE3: what about the rpm jump, is that also normal or should i bring the truck in to have it looked at?

 

I would get that looked at..! I have a 6500lb Suburban that does not do that in DOD mode, sounds like you have a bad cylinder from either a plug,wire,injector,etc. Have the dealer look at that and get the technician to do a ride along so he knows what is happening.

 

Rob

[SouthCo]

I agree, not normal. I can't tell the difference between 4 cyl or 8 cyl. No change in smoothness nor is there even a change in sound in mine.

[dave_benn]

Im going to take the MBRP exhaust off tomorrow, and put the stock one back on. MBRP doesn't include a flex coupling in the kit, so im thinking that that may be it but i doubt it seeing that the exhaust system has been on the truck for about 6,000 miles, and it started doing this about 1,000 to 1,500 miles ago. Since it started it has gotten progressively worse, but it is intermittent. It does it about 80% of the time.

[bigred522]

I am experiencing the same problem with my 2009 LTZ ext. cab 4wd w/ 5.3L. I get and awful shudder/vibration in 4cyd mode. I get the change in exhaust sound, but I figure that would be normal because your running 4 less cylinders. The vibration just started around 30,000 miles though. It also vibrations really bad in automatic and full time 4wd. Dealer doesn't have a clue what's going on!