08 tahoe 5.3 2wd deceleration "rumble"

[akbrener]

My 08 tahoe has been 99% reliable for its 189K life and figured the first big repair order would be coming soon. 08 Tahoe 5.3 2WD and 4L60 trans.

When slowing down to a stop it feels like around the shift down to 2nd gear it gets a bit rough, the engine somewhat flutters or shudders. goes away pretty quick but sometimes if I am cruising though my neighborhood around 15mph it will do it for an extended time. kinda feels like when AFM is engaged and can feel the vibrations.

This has been happening off and on for the last year or so. I did a pan drop fluid and filter change about 10K miles ago and really didnt notice any difference. Fluid was in need of change but not black. Normal driving has zero issues. shifts smooth and holds every gear without slipping. No codes as well.

I did a bit of googling and saw that the torque converter may cause this, but there would be a check engine light associated. As far as I can tell the engine is running well, has a pesky intermittent rough idle in gear, but does not stall.

Curious if anyone has experienced this, thanks.

 

[GreyStone]

My 08 tahoe has been 99% reliable for its 189K life and figured the first big repair order would be coming soon. 08 Tahoe 5.3 2WD and 4L60 trans.

When slowing down to a stop it feels like around the shift down to 2nd gear it gets a bit rough, the engine somewhat flutters or shudders. goes away pretty quick but sometimes if I am cruising though my neighborhood around 15mph it will do it for an extended time. kinda feels like when AFM is engaged and can feel the vibrations.

This has been happening off and on for the last year or so. I did a pan drop fluid and filter change about 10K miles ago and really didnt notice any difference. Fluid was in need of change but not black. Normal driving has zero issues. shifts smooth and holds every gear without slipping. No codes as well.

I did a bit of googling and saw that the torque converter may cause this, but there would be a check engine light associated. As far as I can tell the engine is running well, has a pesky intermittent rough idle in gear, but does not stall.

Curious if anyone has experienced this, thanks.

Are you driving in tow/haul mode

 

[iamdub]

My 08 tahoe has been 99% reliable for its 189K life and figured the first big repair order would be coming soon. 08 Tahoe 5.3 2WD and 4L60 trans.

When slowing down to a stop it feels like around the shift down to 2nd gear it gets a bit rough, the engine somewhat flutters or shudders. goes away pretty quick but sometimes if I am cruising though my neighborhood around 15mph it will do it for an extended time. kinda feels like when AFM is engaged and can feel the vibrations.

This has been happening off and on for the last year or so. I did a pan drop fluid and filter change about 10K miles ago and really didnt notice any difference. Fluid was in need of change but not black. Normal driving has zero issues. shifts smooth and holds every gear without slipping. No codes as well.

I did a bit of googling and saw that the torque converter may cause this, but there would be a check engine light associated. As far as I can tell the engine is running well, has a pesky intermittent rough idle in gear, but does not stall.

Curious if anyone has experienced this, thanks.

Mine did this because of the AFM at low RPM, so I had it turned off to stop it until I could delete it. I guess it had about 160K on it at that time.

Have you watched to see if it's directly related to the AFM? Cycle through the screens on the DIC until you see the "V8 MODE" screen. Watch it next time you're coming to a stop to see if it displays "V4 MODE" when it rumbles then quits right as it changes back to "V8 MODE".

 

[akbrener]

Not driving in tow/haul..

will keep that screen up next time i am driving. I thought about doing the AFM delete but til now i didn’t really have any issues relating to it. Doesn’t burn oil

 

[MrAguirrechu]

Have you checked your motor mounts?
I had the same issue with an 07 Yukon and it went away after replacing both.
I was at about 160k when it started happening.

 

[iamdub]

Not driving in tow/haul..

will keep that screen up next time i am driving. I thought about doing the AFM delete but til now i didn’t really have any issues relating to it. Doesn’t burn oil

I'm still betting on an AFM issue and I'd take this as a warning. My '08 gave me the same pattern of warnings: First, the rough operation at low RPM before the AFM deactivated. Then, a lifter ticking at startup. Then, that ticking began to last longer and sounded like it was more than just one lifter at startup. Granted, mine sits for a week or so between startups, so that doesn't help. Switching to Pennzoil Platinum immediately reduced the length of time and severity of the ticking. Having AFM turned off in a tune made even more improvement and it was almost silent for about 30K miles. Then it started with a single lifter ticking at startup again. Just recently, at 200K miles, I tore it down and deleted AFM and upgraded a few things.

There are upgraded AFM parts available now- the VLOM and lifters are much improved and there's a shield for the relief valve in the oil pan. There's also a redesigned LH rocker cover that relocated the inlet hole in the baffle. If you've had yours since new, you'd know if these parts have been replaced. I bought mine at 147K and it had the updated VLOM and rocker cover, but I don't know if the lifters had been replaced. If I were to open one up for an AFM issue, I delete it altogether and wouldn't even consider installing the updated lifters unless I wasn't replacing the cam.

As Damian lead on, blown engine mounts will make the vibes more pronounced. I didn't replace my mounts until after I had disabled AFM. Chances are, if they're original, your mounts blew out long ago. I wouldn't just replace them to soften the vibes. Fix the vibes and replace the mounts with two of the H3 V8 passenger side mounts.

 

[akbrener]

I'm still betting on an AFM issue and I'd take this as a warning. My '08 gave me the same pattern of warnings: First, the rough operation at low RPM before the AFM deactivated. Then, a lifter ticking at startup. Then, that ticking began to last longer and sounded like it was more than just one lifter at startup. Granted, mine sits for a week or so between startups, so that doesn't help. Switching to Pennzoil Platinum immediately reduced the length of time and severity of the ticking. Having AFM turned off in a tune made even more improvement and it was almost silent for about 30K miles. Then it started with a single lifter ticking at startup again. Just recently, at 200K miles, I tore it down and deleted AFM and upgraded a few things.

There are upgraded AFM parts available now- the VLOM and lifters are much improved and there's a shield for the relief valve in the oil pan. There's also a redesigned LH rocker cover that relocated the inlet hole in the baffle. If you've had yours since new, you'd know if these parts have been replaced. I bought mine at 147K and it had the updated VLOM and rocker cover, but I don't know if the lifters had been replaced. If I were to open one up for an AFM issue, I delete it altogether and wouldn't even consider installing the updated lifters unless I wasn't replacing the cam.

As Damian lead on, blown engine mounts will make the vibes more pronounced. I didn't replace my mounts until after I had disabled AFM. Chances are, if they're original, your mounts blew out long ago. I wouldn't just replace them to soften the vibes. Fix the vibes and replace the mounts with two of the H3 V8 passenger side mounts.

thanks for the detailed response. I have owned it since 2012 and 90k. 2nd owner and i believe i remember the service history had the valves cover replaced, which is why i am assuming i done use as much oil as others..

Will dig into the AFM issue and look at motor mounts as well. It does have a little lifter tick at start up but goes away pretty quick. Have been looking at the parts that need replacement under the pan, have a small oil leak at the pan gasket so might as well knock out a few birds with one stone.

 

[iamdub]

thanks for the detailed response. I have owned it since 2012 and 90k. 2nd owner and i believe i remember the service history had the valves cover replaced, which is why i am assuming i done use as much oil as others..

Will dig into the AFM issue and look at motor mounts as well. It does have a little lifter tick at start up but goes away pretty quick. Have been looking at the parts that need replacement under the pan, have a small oil leak at the pan gasket so might as well knock out a few birds with one stone.

Sounds like textbook AFM failure symptoms. Appreciate that you're getting warnings rather than it just crashing on you while miles away from home.

It's just a small $8 shield that redirects the oil spray from the relief valve when it opens. Actually, I think its proper name is "oil deflector". But, if you're gonna disable or delete AFM, then this part would be unnecessary. Put the money towards an oil plug to replace the valve if you delete AFM and have the pan off to replace that gasket. I have lots of pics and info on all of this in my build thread if you wanna browse.