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Nbs 07-08 5.3l Idle Pattern

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music Senior Enthusiast

music

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OK... I've been driving my new '08 5.3L (alum block) long enough to ask a question. When sitting at idle, I notice a slight, random vibration from the engine that I never noticed on my old '99 5.3L. Is this normal? Before asking about it at the dealer, I thought I'd ask on here, especially since it doesn't affect anything.

 

Question for 2007-2008 5.3L owners: How does your truck idle? 1. Ultra smooth, 2. Smooth with a random vibration, or 3. Rough. For me, I'd say that mine is "smooth with a random (slight) vibration".

HawkeyeOC Senior Enthusiast

HawkeyeOC

Posted
Posted

Smooth with a random vibration...almost feels like a fouled spark plug or something...very slight. My '07 has over 24k miles on it now

zxcv Enthusiast

zxcv

Posted
Posted

Mine idles pretty good - hovers just below 1000 rpm maybe 600-800 rpm range. No vibrations or anything like that...if it's not hurting anything just show the dealer next time your in for service

music Senior Enthusiast

music

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Mine is smooth. Before Justin (Blackbear) adjusted it 25rpms higer it was pretty rough.

 

Really? 25 rpm made the difference? The least amount of added throttle and it goes away... so maybe that's it, just a slight (harmonic) coupling with the engine mounts at idle. If so, it would vary a little by block type, exhaust, etc. I don't want to make this sound like an "issue", since it's not. It's just different than my old truck and, if it can be adjusted, then it may be worth looking at some time.

punmax Senior Enthusiast

punmax

Posted
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My 6.0 idles really rough, but the dealership said if the computer is not throwing any codes, they cannot do anything.

ZZ327 Senior Enthusiast

ZZ327

Posted
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and it ticks loud too. They so build engines like sh!t !

 

O wait.

 

 

mines idles pretty smooth with some slight thumping like it has a cam, I like It!! I think its maybe in the 5-600 RPM area

I dont have a NBS but the 07s at my company are the same way.

matt3 Enthusiast

matt3

Posted
Posted

Have the dealer check for air conditioning lines that are vibrating. I had the same problem and at first they found a loose clip in the engine compartment. That did nothing, I went to a different dealer and they found some loose lines that were vibrating off the engine compartment. I think they were a/c line but, I am not 100%.

 

Hope that helps.

wlvrn1215 Senior Enthusiast

wlvrn1215

Posted
Posted
My 6.0 idles really rough, but the dealership said if the computer is not throwing any codes, they cannot do anything.

 

 

define really rough :thumbs:

 

 

:tear:

rogerf Enthusiast

rogerf

Posted
Posted
Question for 2007-2008 5.3L owners: How does your truck idle? 1. Ultra smooth, 2. Smooth with a random vibration, or 3. Rough. For me, I'd say that mine is "smooth with a random (slight) vibration".

Are you sure this isn't the a/c compressor loading? Mine idles smooth but have noticed a minor stumble as the a/c compressor clutch engages & disengages while the engine adjusts to the change in load. This stumble has been minor on this truck compared to other vehicles I've had with smaller and less balanced engines. Had a Dakota with a 4-cyl where the a/c could double as an engine brake. :thumbs:

music Senior Enthusiast

music

Posted
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Are you sure this isn't the a/c compressor loading? Mine idles smooth but have noticed a minor stumble as the a/c compressor clutch engages & disengages while the engine adjusts to the change in load. This stumble has been minor on this truck compared to other vehicles I've had with smaller and less balanced engines. Had a Dakota with a 4-cyl where the a/c could double as an engine brake. :D

 

Pretty sure... unless the A/C compressor is kicking in when I don't have it turned "on". I actually thought of that and turned the A/C on and off... no difference.

 

One of the above posts pretty well summed up what it feels like, it's more like a slightly modified cam in a street rod... a random jitter, but very, very slight. It's so unpronounced that I doubt most people would even notice, but wanted to make sure it doesn't indicate anything to concerned about. I'll run it and look around to see if anything looks odd, but on first pass, the engine sounds normal from the outside and I haven't noticed anything loose.

 

Other than this observation, the engine purrs like a kitten and runs/sounds/pulls great. Around town, w/ mixed stop/go and a couple of 55 mph stretches, I'm averaging just over 18 mpg with only 500 miles on the engine, although I'm driving pretty easy. Very happy so far!

slimjim2525 Senior Enthusiast

slimjim2525

Posted
Posted

 

 

My 6.0 idles really rough, but the dealership said if the computer is not throwing any codes, they cannot do anything.
Typical dealer BS, why not just try reflashing the computer.
.justin. Enthusiast

.justin.

Posted
Posted
One of the above posts pretty well summed up what it feels like, it's more like a slightly modified cam in a street rod... a random jitter, but very, very slight. It's so unpronounced that I doubt most people would even notice, but wanted to make sure it doesn't indicate anything to concerned about. I'll run it and look around to see if anything looks odd, but on first pass, the engine sounds normal from the outside and I haven't noticed anything loose.

 

The "GM Shake" is extremely common, some worse than others. A slight idle rpm adjustment and modified idle timing (that's the big one) will usually smooth them out considerably. The 5.7L L31 engines generally have a much more pronounced shake, so GM has apparently paid some attention to it.

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