'93 Lightning 10psi doggy? air/fuel??
 

My buddies lightning with a stock motor and a 10psi S-trim on it seems to be doggy sometimes like it has severly retarded timing and then the next stoplight it might run great.

He has an A/F ratio monitor in cab and it is always hanging out in severe lean condition now, even when running boost and 100psi fuel pressure.

It also has a rough idle condition sometimes it will flucuate between 300-1000rpm normally it idles at around 750 rpm.

Could this be the o2 sensor?

If anybody has any ideas that would be great we are out of them

Sounds like a bad ground to me. I'd check the fuel pressure regulator too, and then put in 2 O2 sensors (one for his gauge, and one for the computer). It's possible that the computer is not gettin enough signal from the O2 sensor, or feedback from the gauge.

He has a mechanical fuel pressure gauge on the cowl so we know it is right. Going to replace the o2 sensor.

Where do you think it might have a bad ground?