Anyone up on 99 Chevy 4.0L Vortec engines?

Oops, it's a 4.3 L engine. The engine has one O2 sensor in each manifold (headers now) and a third after the cat. This one needs to be fooled as there will be no cat to read from. I would'nt consider not using the first 2, that would make as much sense as putting a carb on it.

Paul Calman did pass the time by typing:

Google ye for "o2 sensor simulator"

Easy enough to make one, it's just a voltage regulator circuit.

That costs as much as a sensor! I made a regulator for my Goldwing's instruments, i guess I can do one for this lower voltage.

Paul Calman did pass the time by typing:

Yep. But that example was on a ricer page and they tend to pay out the arse for the oddest things like those annoying fartpipes. :)

There's nothing wrong with carbs, if properly setup and maintained. In this case, the engine came with an MPI system, and we are going to use it. Andy will be driving this rig at least 80% on the street.

let me add to that. If properly set up for where you are. A day trip here can take me from 3500ft to 11,000 ft, down to 2000 and back over. A Holley needs re-jetting for what, every 2000 ft of change? This FI system has a barometric pressure sensor that will compensate.