HwyStarJoe

Hey all,

I'm still chasing a random misfire (all cylinders) and I think I've narrowed it down to the spark advance.

The screen shot of the Tables & Maps from ScanXL shows what it looks like when when I run the RPMs up past 3000. The engine has a distinct 'miss' starting around 1800 and is the worst between 2000 and 3000.
I've already done plugs\wires, injectors, intake seals. I had the dyno tune the fuel trims.
I also swapped the front O2 sensors with the unused rears.

The rest of the screen shots are from the same time.
I'm not sure where to start troubleshooting the spark advance. Cam Position Sensor? Crank Position Sensor?
I have no trouble codes... pending or otherwise.

Thanks for any ideas... this is driving me nuts.

HwyStarJoe

MAP sensor?

HwyStarJoe

Nope....not MAP sensor

Mercier

iTrader: (15)

Long shot but have you cleaned your MAF? Easy to do and good basic maintenance. Could the IAC be doing something silly when it shouldn't?

HwyStarJoe

Yeah, everything has been gone over.
From what I understand, the GTO (LS2) didn't have IAC, unless it's incorporated into the MAF.
The MAF is the next logical step but far too expensive to swap simply to troubleshoot.

If I knew what the signals were supposed to look like at all of the sensors (waveforms, voltage levels at different times, etc) I'd snoop at them with an oscilloscope and narrow things down. But I don't know if what I'm looking at is legit.

Mercier

iTrader: (15)

Good point. My LS2 is now LS1 externally so my point of reference is a bit off. It would make sense that DBW cars would have no need for IAC. Good thing, too. that b!tch is like $100 at Autozone.

I would post this in the custom tuning forums..not *exactly* that but I am sure those guys run into this kind of stuff all the time when trying to diagnose an issue with their tunes.

Good luck!