So the cobalt has had quite a bit of work done to it, I did a rebuild with forged internals and did a slight port and polish job on the exhaust valve bowls and runners. Upon the initial start and break-in, the engine ran excellent with only codes for the A/C circuit (which isn't hooked up yet).

My old catalytic converter was hammered to hell, so I welded on a Walker universal obdII 3". I didn't quite get the angle right, and the post-cat O2 sensor wires got damn near cut off from getting pressed into the car. Stupid mistake but I was in a hurry and didn't notice it until the damage was done.

So on my way home today, the car seems to stutter or misfire when I shift JUST as i start applying the throttle. No significant idle issues except a bit of surging at startup. Inspected MAF sensor and cleaned with MAF cleaner, Cleaned throttle body, Checked spark plugs and gap. I am now getting several codes, some for MAF, probably 4 or 5 for O2 sensors and for evap control circuit?!? I'm puzzled.

 

Ok so here's an update. I hooked up a scan tool with the engine running and noticed that my MAF voltage was reading a constant 0.25V. Which led me to believe that it was just a dead MAF sensor. So, I replace it with a brand new one and I'm still getting the same reading. What kind of wiring problem could cause it to only show a constant 0.25V??

 

sounds to me you might have a pinched wire some where, maybe after reinstalling the motor you might of smashed a wire or pinched it some place? I'm not sure without looking at it or hearing it, nor am I positive if it is suppose to even run at a constant .025 volts but if it is constant then that would lead me to believe the wiring is split and grounded out some place. Just a thought..

 

.25*

 

That's a good possibility, i'm going to spend time tomorrow looking at the harness. What stumps me is the constant 0.25V. doesn't change at all

 

Just a thought, did you check your fuse in the fuse box in the engine bay marked emmisions ( I believe it's labeled EMS ). If one of the O2 sensors got pinched and wire was exposed to metal than its possible the fuse might have blown. Just a thought

 

Wow that's exactly what it was. Thanks a lot! I can't believe I missed the most obvious problem. Here I am doing volt drops on the maf and harness.... smh