I own a '97 LT1 with 69K miles on it. Though I did post on the LT1 board, I thought the diagnosis may be general in nature and span across to LS1's as well.
After a WOT run, the engine runs VERY rich even at idle and higher RPMSs. You can see the black smoke and heavy smell of unburnt fuel.
I did register a couple codes indicating my Bank 2 pre-cat O2 sensor was faulty as well as my Bank 1 (driver's side) injectors were running rich.
My understanding of O2 sensors and the PCM is that in open-loop mode (cold engine, heavy load, WOT) the PCM disregards the O2's and runs off a preprogrammed set of values. I do realize that a bad pre-cat O2 will make the PCM do crazy stuff with the fuel and timing, but since the O2's need to warm up to 600 deg. F to function properly, AND that the engine is RICH before the PCM goes into closed loop mode, I don't think the O2 sensors are the culprit. I am still changing both out since all that unburnt fuel most likely ruined them.

My hunch is the problem is something sending a signal to the PCM to dump a lot of fuel in...even at idle. My understanding of the PCM and fuel delivery of multi-port injection is limited...thus needing your advise. Unfortunately, I have the stock exhaust so I cannot verify only the left bank of the engine runs rich.
I am ruling out overpressurization of the fuel system since then both banks would be rich, not just the left side...unless the PCM only sensed the left side (hmmmm)

I also feel that this problem may not be limited to LT1's since the general fuel delivery and PCM interface (with associated sensors) are very similar with LS1's right?

Someone did mention the MAP and I will check that out. I am not getting any backfire or knocking so I am kind of ruling out the Opti (will several dead cylinders make the engine idle with a slight miss--and not a very rough idle-- and pump out all that black smoke?).

Not sure if stock exhaust means stock manifolds as well...but check the header gaskets, a leaky gasket or a leak in a header before or slightly after an 02 will cause a false lean condition and the computer will try to compensate even though it isnt really running lean, so it will go rich as hell, then it will lean it out, and it will keep going back and forth trying to fix a lean condition that really isnt there.

Other than that, if it is bone stock...If im not mistaken, dont quote me on this, but when the engine goes into WOT it uses the values it had right before it went into WOT, and the same with cold start, it uses the values from when it was shut down last or it maybe bases them off of those values. Somebody correct me if im wrong.

Never thought about the exhaust manifold gasket! I'll go check it out, but will be limited to listening tests for now. Yes, it is 100% stock ...no headers, no CAI, no performance chip, etc.)

False leans can also be caused by faulty O2 sensors and misfires, in addition to O2 leaks before the sensors. A false lean causes the PCM to build up the long term fuel corrections in closed loop, adding fuel the engine doesn't need. Then when you go WOT (or more correctly into power enrichment/PE mode), because the long terms were adding fuel in closed loop, the PCM uses those long terms to calculate PE mode pulse widths.

The stock tuning in the LT1 PCM in PE mode only makes things worse, typically setting a target A/F ratio in the area of 11.7:1, too rich compared to the more typical 12.8-13.2:1 required for peak power/torque.

I think you could have gotten the same answers on "LT1 Engine Tech", or on the "Computer Diagnaostics....." forums.

Looking at "LT1 Engine Tech", I see you already have this topic posted there, and have lots of responses. In the future, please post ONLY on the correct forum.

This thread will be closed.