2000 Pontiac Grand Prix

[sturgillbd]

I have been working on a 2000 grand prix for a friend (3800 V6). It had the typical intake gasket troubles. Replaced lower intake gaskets and whole upper intake. Engine had been passing coolant into the upper plenum. Everything is sealed up now and took it for a test drive. I sets a code of bank 1 lean. It only has an 1 upstream and one downstream o2 sensor. Watching the sensor data during a test drive, the o2 swings from .9 down to .02 volts while driving down the road. I assumed the O2 sensor is poisoned from the coolant being leaked into the upper plenum so I bought a new O2 sensor and installed. The ecm never went into closed loop and the upstream O2 voltage was basically locked at .450 volts. It then set a code of little or no activity on B1S1 (upstream sensor). We pulled an O2 sensor out of a running car with the same engine (2 years newer) and installed. O2 voltage stayed at .450 like the sensor wasn't even plugged in. Re-installed the old sensor and it instantly started the wild swings between way rich and lean. Compared all of the sensors and all have the heaters, signal and ground in the same places on the plug. The original was an AC sensor. The new sensor was denso and the used one that was pulled from a running car was a delphi. I have traced wires with a meter from the O2 sensor to the ECM and all are connected well. Checked the grounds on the car and they are fine. The worst ground had 34mV between the battery post to that connection. Cleaned it and it dropped to 15mV. I am going to attach two screen shots of the scanner screen in live data view taken 12 seconds apart with vehicle in park and at idle. This one is just weird. I also get a P0300 (random multiple misfires) when on a test drive. Fuel pressure starts out at 50 with key on. Normal driving 43-45 psi. During hard acceleration pressure goes to 52-55 psi. During hard acceleration, it feels as though it goes way lean and the scanner shows this in the live data. MAF shows good flow numbers during test drives. TPS is faily linear with no dropouts on scanner. MAP sensor seems operational. Engine cold, the CTS and IAT are within 1 degree of each other and seem pretty accurate according to outside temps. Has anyone ever run into anything like this??? I have also sprayed carb cleaner around intakes looking for vacuum leaks and none have been found.