Becker

iTrader: (4)

Hey guys I've been fighting an issue while working on my 06 V. I am currently stock intake and just cat back only, but I've been working with a friend on a diablo tune. I log a lot and he adjusts the maf and ve tables with diablos software.

My question is, can a spark plug gap changed from .060 to .040 change the tune a lot? Mid way through the logging and tuning my friend said I went way lean. Originally I started a bit rich he said but all of a sudden I am lean. Anyways now I have been experiencing LTFT on both banks up to 12%+. I've done every check I can think of to look for vacuum leaks, fuel pressure and etc to find something. Nothing has changed. Maf is clean as well.

I did however change the plugs sometime in the tuning process (can't remember when, wish I could to see if it directly affected the tune). But I was taking a look at the plugs removed and they seemed to be gapped at .060 and all showed a slightly rich burn on them. I replaced them with stock AC delco at .040.

Could the change affected my burn conditions this much? I would pull the plugs but I'm out of the state at the moment, but I can't stop thinking about this. Also I do get a slight ping at high rpm on hot days.

If anyone could kindly throw some knowledge my way I'd greatly appreciate it!! Also a suggestion on what I should do now. Start the whole tuning process over with the .040 plugs? Swap in some .060 plugs and log some data and go from there or something else???

Thanks guys,

jimmyblue

iTrader: (11)

Misfires can totally whack the O2 sensor's accuracy which
depends on the gas being fully combined (not a HC + free
O2 chunky soup). And even before that, increasingly poor
burn-completion or even bad burn-positioning affects
cylinder scavenging and the relation of in-taken mixture
to sensed residual O2 (and then interpreted AFR).

High plug gaps are prone to blow out or fire weakly and
make a poor "kernel" at higher cylinder pressures (WOT).

So don't expect dead-nuts AFR on one pass. Have to get
to roughly-right, and take another pass around the loop
to close in on best-best AFR-spark combo, pointwise.

Becker

iTrader: (4)

Thanks jimmyblue very good information there. I'm just trying to understand what my next move should be? I'm on vacation now but when I get home I'll have a little time to pull the plugs. Wondering if I should change the gap on them. Totally stock engine.