Hey guys,
          I need your help on this one(again). My car is backfiring and loses power when i boost and at 3/4 to WOT. It wasnt to bad when I gapped my plugs at .025 but at .028 it is real bad. Here is a list of what I did put on.
AC Delco plugs
AC Delco wires
Kenny's chip
stock(original)crossover
rebuilt turbo
Every sensor has been changed TPS, MAP, IAC, crank position, knock, O2, used ICm and coils from spare parts bin. All of this gives me the same result.
I know it is me, but i am lost the last thing in my eyes is I messed the cam up.
All new grounds and power wires ran as well
The first weekend with kennys chip car ran great next weekend like crap
                                             Shawn(from PA)

You need to have your crossover fixed.  When I had my stock crossover, my TGP bogged down at high throttle openings and felt weak above 4,000 RPMs.
Kenny can do a crossover for ya, contact him.

What about the backfire at high boost and when my plugs are gapped smaller its not that bad. Possible too much air getting in motor from leaky crossover?

Does your wastegate open/flow freely?

as far as I know my wastegate works good.

Sounds like it could be a bad intake gasket leaking boost.  How does the car idle?  sounds like either intake or boost leak pretty..

The car did idle rough , but I think with my adjusting the modulator vavle has fixed it. It idled fine after I adjusted it havent driven it since. I have replaced all the vacuam lines also, upper intake gaskets are new lower one is old. Thanks guys I appreciate all of your input.

What modulator valve are you referring to ?  If the lower intake gasket is old, i bet thats your problem...

the transmission modulator vavle. Thank you I will replace the lower intake this week weather permitting.

id start with the crossover, the LIM will not cause that, the LIM is more like coolant being dumped into the oil and destroying the bearing, or leaking oil out, not exactly common on these cars

I didnt think so when my 2.8 cavalier intake gasket went it didnt run like this. I am going to take the shield off tomorrow and look to see if it is blck anywhere. Thanks

not common on these cars?  The LIM gasket goes bad on all 60 degree v6s - and you will leak your boost out right into the crankcase...and loose power.  When i first got my car, the EGR hose off the crossover was broken right in half... yea i had a high idle and didnt make much boost but i could definatley go WOT and no backfiring or bogging out...  Never know it could be something simple.  how old are your injectors?

my injectors are new yellow tops. Man getting mixed feelings I will change LIM and check crossover, just for peace of mind

the LIM gasket is most likely not your problem.  The newer models are known for problems, the old school 3.1, before the 3100 and 3400 variations, are not likely to fail. 

who is the manufacturer of the O2 sensor?  Start with the crossover, almost 100% guaranteed that's your issue.  If your O2 is Bosch take it out and throw it away, get yourself a AC Delco. 

Yes it is a bosch O2 sensor and I know it should be replaced but I just bought it so I was hoping to use it for a little bit atleast. Well funds are slow due to winter so crossover will wait for now. runs great as long as i dont get on it. Thank you guys.