Running rich

After a strong rev. up of the engine (during an emission test) our 3.1 Vin D Pontiac TS started to run rich.

Now there's an awful smell coming from the tail pipe, lots of gray smoke, the snow in the back is getting black and the engine is hesitating when you press the gas pedal.

I've just changed the EGR valve but this didn't improve things at all.

The plugs, Bosch, changed 2 years ago, are fouled (just cleaned them up). Oil, changed 2 months ago, is already diesel-black.

The air filter, spark wires (ACDELCO), distributor cap, rotor and ICM are changed recently. Cooling system is ok (new thermostat).

Any ideas where we should go from here?

If the Plugs are Bosch Platinum .... Throw them in the trash and get either NGK or AC Delco.. Even Autolite...

You are running ultra rich... Is the SES light on at all?

No SES light.

Just ordered a set of ACDELCO's RapidFire and an ALDL OBD I to USB cable to see the actual running data.

A throttle body injector that is blocked-opened is a possibility. THere are 2. Peeking visually into the TBI can provide a clue, or tricking the wiring to drive one injector at a time .... I doubt a false O2 reading can have such an effect...specially since O2 control happens only after engine has warmed up...unless that is the case.
www.avigex.ca/xport/injectors31_1.jpg
www.avigex.ca/xport/injectors31_2.jpg
www.avigex.ca/xport/fuelcontrol31.jpg
THe blockage can be mechanical or electrical (shorted grounding transistor).

Thank you LMP for the documented answer!

I wonder if this problem (Injector) would show on a diagnosis software like WinALDL or TTS Datamaster.

We just ordered an ALDS OBD I to USB cable that I intend to use in reading this engine parameters on my laptop.

The code list for the 3.1 is quite limited, and in any case, would not show a mechanical blockage, except for its consequences, eventually.
www.avigex.ca/xport/codes31.jpg

There's no code stored (I checked with the paper-clip method) but this software http://www.aldlcable.com/sc/toplevel.asp?cat=0 seems to show a lot more than just a code.

I will post back as soon as I have the ALDL/Laptop setup in place.

I am especially interested in the differences in engine operating parameters between this car and another Pontiac TS SE with the same engine running great.

We finally got the ALDL OBD I to USB cable and diagnosis software to go with it. :)

Fortunately we have two Pontiacs TS with the same 3.1 TBI engine setup to compare so here are the readings:
1. the good Pontiac sensor data
http://www.pieseamerica.com/GOOD_LOG.htm

2. the bad Pontiac data
http://www.pieseamerica.com/BAD_LOG.htm

I have marked in orange the times when the engine died completely (usually when coming to a stop at a traffic light).

Can anyone make out some useful hints from this data?

Just changed the O2 sensor & spark plugs.

You can find the new ALDL Log at http://www.pieseamerica.com/NEW_O2.htm

I have marked the times when the car died at idle, usually when coming to a stop after braking.

So far EGR, MAP, O2, ICM, filters and all the ignition components were changed without bringing any change in the engine's behavior at idle. Over 650rpm/s everything is great - pulls fine, mileage is good, no hesitation or stalling.

Any idea on what to look-up next is greatly appreciated!