I had my tuner come by to fine tune my ECM yesterday, and we found a problem while at wide open throttle. It was running fine until 5600 RPM, then misfired from then on. He said the airflow readings were odd, but I can't exactly remember in what way. Due to the size of my cam, we couldn't get a reliable misfire reading. Anyone ever have this issue? My setup is an LQ9 shortblock with L92 heads, LS3 intake, 92mm DBC throttle body, and a Livernois 2C cam. All in a Nova. The Mass Air Flow sensor is in the air intake tube about a foot before the throttle body, and is an aftermarket unit. Any suggestions would be appreciated. Thanks.

-Michael

 

Oh, I want to clarify that it misfires from 5600 RPM and up, but is still fine under that, and the MAF spikes high at that point.

 

I have that same cam in my G8. What springs? What MAF? Do you have a log? Tune file?

 

I don't remember off the top of my head what springs they are, but they are correct for the cam. A factory GM MAF, and I don't have any kind of file or log for it. I did, however, discover that I am probably making more power than I had anticipated and I think my fuel pump isn't supporting the engine's needs at that RPM. I am installing a better pump and putting it in the tank today. Hopefully that handles it.

 

Seeing a log would definitely help. You said the MAF spikes when the engine starts misfiring. I would be concerned about either having a faulty MAF or you're maxing the MAF out. What brand of MAF do you have? What type? Can you get a copy of the tune file and log?

 

I had an aftermarket replacement MAF, but swapped it out for the MAF from my Saab 9-7x (Trailblazer) with a 5.3 to no change. Not sure the differences in type to be able to tell you what type I have. If the fuel pump doesn't take care of it, I will see if I can get the tune file from my tuner. I do know that whatever the problem is is affecting the O2 readings on both banks equally. I'll let you know what happens after the pump (I was wanting to go in tank pump anyways, so I figured why not start there). Thanks!

 

Yeah, see if you can get AT LEAST a log. The engine MIGHT be going off of the end of the MAF table. You said the MAF spikes so... May be time to go SD?

 

In the forced induction world we start to get spark blow-out when even running mild boost. You could try tightening the gaps a bit just to rule that out.