Hey guys! I'm having a bit of a problem with my 02 Sierra Denali. Before we get started, the truck has the original lq4 with 180,000 miles on it. Only mods are new ngk plugs, msd 8.5mm wires, dynatech headers, cutom midpipes with hiflow cats, a corsa 3" catback, and a zippy custom tune using hp tuners.

The first thing I changed was the spark plugs, and wires, after I changed them, I noticed the truck was missing a bit. I haven't checked them for cracks yet, but that's the next thing on the list.

With zippy's tune, the truck was running over 50% lean between both banks at wot. The only time it didn't run terribly lean was at idle. Zippy wouldn't tune anymore until we fixed this problem. So, I took it to a mechanic that said it was a tuning issue and they retuned it in person. long story short, the truck runs rich now at idle and normal driving, and then reverts back to max lean at wot.

I've cleaned the MAF, I've checked fuel pressure, and I've checked the k&n for leaks.... not sure really what else to do.

Can anyone help? I just wanna go fast

 

Take it to a tuner strap it down with a wideband and a competent custom tuner can sort it out fairly quickly.

You can take B12 and spray the intake gaskets and see if you hear a change in idle or the 02 data goes crazy then it's time for intake gaskets. Scrap the K&N filter put a dry filter in and wash the MAF with carb cleaner if it's oiled up.
Have you changed the fuel filter?

 

I tried to use a volant, but I couldn't get it to seal or clear my stupid fan. So I'm saving it until I can get e-fans. And I'll try that. Thanks!