Reason(s) for V8 not being smooth at idle

[KingCake]

Originally Posted By: yugrus
Here's what I managed to get out of my Maxidas scanner. Fully warmed-up engine at idle, in park.
Desired idle: 600 rpm
Engine speed: 593-616, varies fast, and that's the issue.
MAF: 5.27-5.33 g/s
Air flow calculated: 4.99-5.21 g/l
APP indicated angle: 0%
TP indicated angle: 3%
MAP: 32KPa
Intake manifold pressure: 69 KPa

Commanded A/F equivalence ratio: 1. This stumbled me. It was I red, and I don't think that this is right...

HO2S B1S1: between 70 and 800 mv, cycling nicely.
B2S2: 725 MV
B2S1: same as B10
B2S2: 700 mV

Fuel trim cell:6. Not sure what it is, but should be 0...30
Vehicle speed:0
TSC slip speed:between 5 and 15. Could be -200...4000

No EGR valve on that motor, as far as I know.

Will wait on what you guys think...



Your truck is fine.


Quote:
Engine speed: 593-616, varies fast, and that's the issue.


That's NOT the issue. Literally every engine will fluctuate +/ 50rpm constantly.

 

[KingCake]

Originally Posted By: brave sir robin
Originally Posted By: yugrus


Will wait on what you guys think...


I think your truck is fine and you are looking for a solution to a non existent problem.




Yep.

 

[yugrus]

Thank you folks!
I was really itching, and went out and adjusted idle speed to 650rpm in drive. Left 600rpm for park/neutral. Then adjusted injector slope by 3% down, the average amount of the positive LTFT at idle. I thought it was better when I started the truck after that. Will report tomorrow on what I feel and think. Will have my Scangauge II on it at all times!

 

[Silverado12]

My opinion is with the idle at 600, it's going to shake a little because IMO that's too low an idle. FWIW I checked my old timer 4.3 V-6 yesterday and it was idling at 750-800 according to the gauge on the dash.

 

[brave sir robin]

Originally Posted By: Silverado12
My opinion is with the idle at 600, it's going to shake a little because IMO that's too low an idle. FWIW I checked my old timer 4.3 V-6 yesterday and it was idling at 750-800 according to the gauge on the dash.


The stock idle speed on his motor is around 500 rpm. Most truck V8s idle between 5-600 rpm in gear

fwiw the stock idle speed on my 68 electra is 550 rpm (IN gear) and will drop to around 450 with the ac on. The v6 in my Pathy idles at 750 with the manual transmission and is lower with the automatics while in gear.

 

[yugrus]

I raised RPM by 50 and I feel comfortable, for now. The shudder is still there, but is much less noticeable. I guess I will never get to the bottom of it, so this makes the truck more enjoyable. Thank you everyone for your input, you're a great community!

 

[ls1mike]

Nature of the GM tune. My 02 does it, my 14 Caprice does. The idle is set low.
Not an issue. You want to see a weird idling LS? I will take you for a ride in my Trans Am with a big cam.

 

[DriveHard]

My 2011 6.2L idles about 550 in gear. While it is not silky smooth like my wife's I6 or the old BMW V12 I owned...it is pretty smooth, just enough slight vibration to let you know it is alive. That vibration increases if the A/C is on of course, or if I have been sitting still for a while and the fans are running at high speed (more electrical drag).