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Rough idle on the 6.0

Old Feb 23, 2024 | 10:11 AM
  #41  
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it was at around 58ish, no dips
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Old Feb 24, 2024 | 01:10 AM
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I'm curious what the oxygen sensors see through one of these events. All the way from a couple of seconds before to a couple of seconds after.
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Old Feb 24, 2024 | 09:14 AM
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ill watch it today or tomorrow and record and rewatch it... I will pull up both upstream and downstream for bank 1 and bank 2 on the scan tool and watch for spikes/ dips
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Old Mar 3, 2024 | 05:02 PM
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all normal, I have a buddy that tunes the LT and LS motors and he said that in his experience they all run a little rough being an OHV design so trims and all that looks good, if it gets worse I will look into it more, I am just used to the bmw inline 6 perfect running engines because they are dohc so its alright
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Old Mar 3, 2024 | 06:49 PM
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Sounds good.

I guess we don't have a good measure of what "run a little rough" means. Nobody can feel or hear my 5.3 LS idling if the HVAC blower is above 2 clicks with 320,000 miles on it, and it is completely smooth at speed. Plenty of OHV designs run smooth with conservative cams.

For yours, I'd look at compression tests next.
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Old Mar 3, 2024 | 09:28 PM
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K ill do a comp test when I can, might be a lil bit since you have to remove the dog house and plugs are a lil hard to access. I wouldnt say it shakes the car at all, just if you sit in the car you can feel a little tiny jerk or something every few seconds and if you look at the engine oil filler neck you can see a little tiny bit of a shake to it, nothing crazy concerning honestly just feels like spark plugs around 70k when they are starting to wear if you know that feeling. Runs literally perfect now anything above idle.

I was told that Chevy and many other companies runs their v8'* a little bit lean for the afr at idle to help emissions, maybe thats why
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Old Mar 4, 2024 | 07:45 PM
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Compression seems fine, I did notice voltage is a little bit odd at times, like 13.79v at idle when warm, I looked at my main battery to engine block (which is the same strap that connects engine ground to chassis) and its all green and starting to tear a little bit at places, i think this may be somewhat of the issue. I also feel a tiny bit of engine bucking when just creeping forward barely applying the brake pedal
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Old Mar 4, 2024 | 11:51 PM
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Originally Posted by TopLock
K ill do a comp test when I can, might be a lil bit since you have to remove the dog house and plugs are a lil hard to access. I wouldnt say it shakes the car at all, just if you sit in the car you can feel a little tiny jerk or something every few seconds and if you look at the engine oil filler neck you can see a little tiny bit of a shake to it, nothing crazy concerning honestly just feels like spark plugs around 70k when they are starting to wear if you know that feeling. Runs literally perfect now anything above idle.

I was told that Chevy and many other companies runs their v8'* a little bit lean for the afr at idle to help emissions, maybe thats why
It shouldn't do that. Not sure who is telling you this stuff, but these overly-general tidbits of anecdotal hearsay aren't really doing anything for us except possibly clouding the diagnostic process. If the engine is in good shape, it will run smoothly. If you can feel a little tiny jerk or something every few seconds but not all the time, then there is a problem.
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Old Mar 4, 2024 | 11:51 PM
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Originally Posted by TopLock
Compression seems fine, I did notice voltage is a little bit odd at times, like 13.79v at idle when warm, I looked at my main battery to engine block (which is the same strap that connects engine ground to chassis) and its all green and starting to tear a little bit at places, i think this may be somewhat of the issue. I also feel a tiny bit of engine bucking when just creeping forward barely applying the brake pedal
What are the numbers?
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Old Mar 5, 2024 | 08:13 AM
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Not sure what you are really saying here. Obviously it shouldn't buck when creeping forward, I never said it should. I was just saying in my experience and several other peoples experience, these large ohv engines, especially 6L and above, have a mildly aggressive camshaft from factory so they idle a tiny bit rough. Now the validity of that is probably to be decided. In the meantime, yes, I am aware that my vehicle should not have a little bit of bucking when creeping in traffic. The rough idle is always there, just some days its a tiny bit better. In cold weather on startup its the same, but warm idle when ambient temp are lower seems a tiny bit better.

I did some research and Chevy actually is one of the companies that runs a leaner afr at idle to deal with emissions, for example a lot of companies run really close to 14.7:1 at idle. Most of the b48 models from bmw run 14.4:1, but Chevy and several other companies do it so there are less emissions. That would easily explain why I see perfect fuel trims, but still a tiny bit of a rough idle.

Comp is around 135 on all cylinders, give or take 2psi
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