LC9 Erratic Chart Lines / Knock Retard with a Phantom Miss - Log Attached

[lanche5.3]

I have a 07 Avalanche with a 5.3 in it that's driving me nuts, it's been months. Had multiple mechanics look at it. One day it just started running terribly and fat.

All stock except DOD was deleted in the computer. Shutters bad at idle and choppy under power.

Been through injectors, fuel pressure test, plugs, wires, sensors, compression test, exhaust gas dye test, even replaced the motor mounts. All is well. Zero Codes. Still runs poorly.

My obd2 reader shows a miss on cylinder 2 but HP tuners does not. The only evidence I have is this attached log.

Under power, MAF/TPS/LOAD/TIMING all start to oscillate. Timing is all over the place and it knock retards.

Someone please take a look at this log, it's from a cold start. 20 minutes worth of log with a WOT portion in it, lots of stops and starts. You will see what I am talking about.

Any help would be extremely appreciated.

2007 Avalanche 5.3 LC9.hpl

[5FDP]

What kind of fuel are you running?

In the log the commanded air fuel ratio is about 13.5, meaning it's running around 20% alcohol content. If you are running regular 87 octane with E10, that means the virtual flex fuel is throwing some of your fueling off all the time. Virtual flex fuel is pretty much garbage and most people disable it.

[lanche5.3]

Running 87 currently, I've tried different octane levels to no avail. I'll disable that and report back.

[lanche5.3]

2007 Avalanche 5.3 LC9 - post flex delete.hpl

The log above is after I deleted the flex. Seems to have leaned out the trims but nothing has changed regarding knock retard and rough idle.

In this log I added all the knock channels, downstream o2 and some other stuff I thought might be useful.

You can see below what I am feeling at idle.

idle.JPG

[5FDP]

Raise the idle rpm by 100. These engines always seems to be unsteady when they try to idle at 500-525rpm. I always raise them to 625-650 and it really smooths them out, some people even do 700rpm.

You can smooth out the over/underspeed spark correction tables too, make them less drastic of change. Make them only do +/- 8 degrees of timing instead of the usual 20+ degree swings. Aim for 18-20 degrees of idle timing.

Also getting rid of knock at random on part throttle can be tough, some engines just always do it. Some will make the knock sensors less sensitive and I would also disable burst knock completely.