silver-mod-o

iTrader: (15)

This is on my wife’s ‘12 Denali XL. I recently replaced the valve cover gaskets and grommets due to a leak developing on the driver side. While I was there I replaced the 130K mile plugs. We went on a road trip shortly after and averaged 16-17 on the trip loaded down running 75. Which is about average for this thing on mid-grade fuel, E85 is hard to find around here. I’ve noticed a decline lately and checked it. It’s down from 14ish around town to about 10.5. Still runs and drives fine and the only recent changes being the plugs. I installed the same TR55’s I always run in these things N/A but I’m considering going back to an OEM Delco plug and new wires. Are there any other common problem areas on the 6.2’s that cause the mileage to drop like a rock???

FFDP

iTrader: (2)

Can you see live data?

I'd be curious if the virtual flex fuel is stuck, causing it to burn extra fuel. Unless you installed and wired in a real sensor.

silver-mod-o

iTrader: (15)

Yeah. I’ve got HPT. Just haven’t scanned it yet.

madmann26

iTrader: (7)

What’s the off chance you’re getting fuel with more ethanol?

ZO6Ted

Oxygen sensor? Hell idk...where's my beer now.

silver-mod-o

iTrader: (15)

Might have been a bad tank of fuel, seems to be doing better now though. It’s up to 12.5 or so. I’ll watch it over this week.

GMNUT

iTrader: (13)

I've never had luck with the tr55's on these trucks. I always run the iridium plugs, no messing with gap and they work awesome. ACDELCO 41162.

smokeshow

iTrader: (16)

If it's stock, run stock plugs. Don't reinvent the wheel.

swathdiver

Yeah, run ACDelco plugs and if the O2 sensors haven't been changed, graph them to see if any are getting lazy. My mileage went south due to bad cats. First one and then the other. No codes at first, then occasional and then all the time. Mileage came back with Magnaflow Y-Pipe and Cats. Got better with fresh O2 sensors. Improved again with drag reduction clips on the brake pads.