Starting to wonder

[aarolar]

I am really starting to wonder if someone may have at some point put a cam in my truck, I have a little annoying stumble at idle that comes and goes. We had my truck hooked up to a Genesis back a few weeks ago and the statement was made that my MAP was alittle low at around 9. To add to it I have absolutely no valve train rattle at almost 200k miles which is almost unheard of. Anything above idle and it runs like a top, I am getting 12.5-13 MPG mixed driving which is about right for my truck. I guess the only way to really know what is going on would be to pull it down and see what I have but that seems real counterproductive IMO. Would someone that was good at EFI live be able to tell something by reading the data?

 

[99'Yukon]

I have also been experiencing this off and on as of lately. Only does it during an idle state, whether in park or foot on the brake in drive and resembles somewhat of a misfire or rough stumble like you said. Not really even enough to drop the idle more than 100 rpms, checked the plugs and all were very clean(no carbon build-up, etc.). If you figure anything out let me know.

 

[Horns]

Only way to know is to degree the cam.

~Via Mobile

 

[RHamill]

What if you brake torque it with a scan tool and monitor misfire counts, usually a bad coil will show a misfire with brake torque. Just dont brake torque for more than a couple seconds at a time as its bad for the transmission.

Clean your MAF sensor really good and recheck for the proper specs.

Check the resistance of all your wires while jiggling them around.

Try running a full tank of 89 octane, I had a 09 GMC Yukon Denali on my hoist with the 6.2 had a very subtle stumble at idle only, replaced plugs, wires amd did a full fuel induction service, still had a stumble, so I filled it with 89. You could put a cup of coffee on the top of that motor and it wouldnt even spill.

 

[99'Yukon]

What if you brake torque it with a scan tool and monitor misfire counts, usually a bad coil will show a misfire with brake torque. Just dont brake torque for more than a couple seconds at a time as its bad for the transmission.

Clean your MAF sensor really good and recheck for the proper specs.

Check the resistance of all your wires while jiggling them around.

Try running a full tank of 89 octane, I had a 09 GMC Yukon Denali on my hoist with the 6.2 had a very subtle stumble at idle only, replaced plugs, wires amd did a full fuel induction service, still had a stumble, so I filled it with 89. You could put a cup of coffee on the top of that motor and it wouldnt even spill.

Already checked most all of that. Good idea that it might be coil resistance because if I'm not mistaken the one on my rig is OE, so I might just go ahead and get another seeing that it's about time for a new one anyway. Speaking of the 89 octane, I usually won't run anything but 89 with a seafoam treatment maybe every 2 or 3 fillups. For some reason 87 just doesn't run right in mine causing it to spit & sputter, and it seems like running higher than 89 it wants to burn it faster which sounds strange I know lol. So I tend to usually just stick with my 89 Exxon

 

[SCOTTYINWV]

Mine runs like piss on anything under 91, but I am cammed and untuned running stock timing.

 

[99'Yukon]

Mine runs like piss on anything under 91, but I am cammed and untuned running stock timing.

My next investment will for sure be a black bear tune! I heard it makes such a difference, and I won't have to go out and spend $500 on a good handheld

 

[aarolar]

It tried to die on me today in the wal-mart parking lot, started missing badly I planted my foot on the brake and revved it up and it went back to idling fine again. I am starting to wonder about the ignition module or coil now.