I have a 1991 Trans AM, 305, auto, TPI. Fresh rebuild, SLP chip (ran ok before rebuild). Only changes were adding 1.6 roller rockers and headers with exhaust. Removed air tubes.

Currnetly it is running very rich. It stalls and idles rough. I obtained an aldl cable. The MAP kPa sits at 65-75 when idling, when giving some gas it drops down into the 30's. From my research on this site, the kPa should increase with throttle. The o2 sensor sits at .9 and higher (rich). It sometimes jumps down to the .1 and .2 range. The INT and BLM drop to the low 100's and sometimes lower. Always in cell 4. Once in losed loop it will get some knocks and retard timing 3-9 degrees.

Here is what I have done so far:

Checked the fuel pressure, 45 engine off, 48 when running.
Plugs, cap, and rotor are fairly new. Getting spark. New MSD Blaser ignition coil.
New o2 sensor.
The injectors are all at 17 ohms and hold pressure after shutting off, they are almost new, very few miles.
Changed fuel filter.
Checked for vacuum leaks.
Adjusted TPS.

Still planning on checking the egr system. Also, is the MAP sensor just bad???
Any other ideas or am I at all on the right track??

Thanks!!

 

Low Vacuum (open to the air)

High Vacuum

At idle, vacuum will be 10 - 15 inches gauge, 50 - 70 KPA (the bigger overlap cam, the less vacuum, more KPA)

at high idle 1500 - 2000 rpm, it will raise to 20 - 25 inches gauge, 20 - 30 KPA

at high rpm/load 5500 rpm (WOT), 1.5 inches vacuum (4 b carb) and 3 inches (2 b carb) or 90 KPA for TPI

0 inches gauge, 30 inches Hg, or 100 KPA = barometric pressure = atmosphere

 

So if I understand the chart, my MAP readings are ok. What else that I havent checked could cause the rich condition? Timing? I will have to find a timing light.

 

Do a search on "cell 4" in TGO. The richness goes with the "stuck in cell 4".

Real low O2 cross counts and volts will richen the mixture at idle.

 

I checked the timing today. I was a 0. I advanced it to 6 and it is running much better now. I drove around and did some data logging. It moved out of cell 4 and sensors looked ok. It now idles a little high, so I fixed one problem and may have another.