Ferocity02

iTrader: (60)

Just curious if misfiring at idle is normal with a bigger cam. My 5.3L has a 212/212 114LSA cam and it is misfiring slightly at idle. Scanning with EFILive shows is misfiring about equally on all cylinders. If I let it idle for a couple minutes I'll get a P0300 code. I'm still running a stock tune however. I already changed the plugs, plug wires, and coils. I don't think there is a vacuum leak. I think the misfiring is causing me to fail smog at idle, too much hydrocarbons. Above idle speed it doesn't misfire at all.

Anyone have any thoughts? I suppose the tune could use some adjustment but I'm not sure where to start. Thanks!

badazz81z28

iTrader: (6)

I have heard larger cams can give the computer a false indication of a mis-fire at idle.

But the question is...Why are you running it without a tune? Maybe you really do have a mis-fire, that's not a big cam. The ECM diagnosis a mis-fire by the crank sensor, is it running like crap?

Ferocity02

iTrader: (60)

Its not tuned yet because I'm just trying to smog it right now, and once that's done the turbo kit is going on. So I'd prefer not to spend days dialing in a tune which I'm going to be starting over with in a few weeks. I also don't have a wideband setup yet. It runs great! Can't even really tell its misfiring except for the code, what the EFILive log says, a light smell of fuel out the exhaust at idle, and being 36% over the HC limit at idle. At 2500 RPM it's about 92% under the HC limit. This tells me the cats are working. But something is not right at idle and it's probably a misfire.

I've attached a log of misfires on a drive home.