V4 Mode Engine Trouble Noise

hmb2016 · May 31, 2011

hey guys.. you mightht have seen my post about my locking rear diff trouble and tpms light trouble on here but i figured since my truck is in the shop for a few days i might as well tell them about another problem... when traveling on the highway at 65 to 75 mph when it kicks into v4 mode it sounds like my engine has a bucket of bolts rattling around in the engine.. any help as to whats going on here?? this is not the typical crappy noise v4 mode makes. it is a new development within the last 500 miles or so

BlackZ71Silverado · May 31, 2011

Sounds like you are a victim of the infamous AFM lifter failure. Is the garage going to replace the lifters for you?

hmb2016 · May 31, 2011

dang! what all is involved in that process? also is that covered under warranty?

pm26 · May 31, 2011

dang! what all is involved in that process? also is that covered under warranty?

I think that the 100k miles powertrain warranty covers the AFM lifters too. Except that they will probably install the same crappy kindof lifters in your truck. How many miles on your truck now?

pm26 · May 31, 2011

hey guys.. you mightht have seen my post about my locking rear diff trouble and tpms light trouble on here but i figured since my truck is in the shop for a few days i might as well tell them about another problem... when traveling on the highway at 65 to 75 mph when it kicks into v4 mode it sounds like my engine has a bucket of bolts rattling around in the engine. any help as to whats going on here?? this is not the typical crappy noise v4 mode makes. it is a new development within the last 500 miles or so

That's the sweet sound of AFM lifter quality installed in your truck.......

hmb2016 · May 31, 2011

56,000 miles

abschnick · June 1, 2011

Can you describe the noise a little better. My 07' cc nnbs with AFM makes a vibration noise when it is in the V4 mode. I can feel it in the gas pedal. As soon as I hit the gas and it goes into V8 the vibration is gone.

MaverickZ71 · June 1, 2011

Could it be your Magnaflow replacement muffler? How long have you had it? The General had a helluva time tuning the stock muffler to minimize out-of-phase cylinder firing pulses when in V4 mode. On an aftermarket muffler, it'd probably be best to get your PCM tuned to turn off the AFM.

oldmann · June 1, 2011

Check to see if there is a hose or wire loom very close to or touching the dipstick tube on the passenger side of the engine. I zip tied mine to something and the noise stopped!

ljburns · June 1, 2011

Mine does this, but only at low RPM. It sounds like some metal rattling around under the truck. To me, it sounds like it is coming from somewhere in the exhaust. I only here it at around 900 RPM when in 4v. When im coasting in the neighborhood around 20 mph the truck drops to 4v, very slightly apply the gas just enough to keep the speed on level ground, and you can hear it. It is not associated with the frame or anything touching the frame as I can only here it with the windows down. The sound can not be heard at higher RPM when in 4v. Haven't had time to take it in yet.