Larry

I could use some advice on this, I've never tried to tune a car after a cam change before. I played around with a stock $8D motor for a while but am new to MAF. The motor is 355 vortec heads, lt4 intake, hotcam, MAF $6E. Runs good over 1200 rpms open or closed loop. Idles good at 750 rpms in open loop but rough in closed loop. Blms go to 108 at idle and car shakes really bad but never stalls. Idle speed is rock solid at 750. Blms obove 1000 rpms average 128. I tried taking out fuel in the lower maf table and it helped the open loop idle but closed loop blms still go to 108. Taking out more fuel makes it worse. I tried adding and subtracting timing a few degrees but that doesn't help. Fuel pressure holds at 44 psi, only dropped 2 psi overnight. The car starts instantly hot or cold and idles great cold. New injectors, coil, plugs and plug wires. Any way to keep it in open loop at idle or is that just a bandaid? Or a better way? Thanks for any help you can give me. All this thinking is making my head hurt!

Sonar_un

Man, don't even get me started

I had that same problem with my $8D. Open loop idle was a dream. Perfectly stable, ran great, etc.

Closed loop hit, and all hell broke loose. Car wouldn't not idle, to the point of dieing.

Take a look at your O2 sensor. If you have headers, think about running a heated 02. It deffintley helped me.

RednGold86Z

iTrader: (1)

Sounds like a fooled O2 sensor problem or the cam requires rich. It seems to be fooled high (ECU trying to make it low with the 108 BLM) or hating stoich. The way to combat this is to let the ECU think high O2 volts is OK. There's a table for Closed Loop Rich/Lean Threshold vs Airflow at 046B. Raise those values in the idle airflow region. Don't go crazy here, try 600-700 mvolts.

Hope it works for you.

Might want to raise the idle speed too.