I have had this problem for many months now and now I would like to start working on it again.. My 97 6spd Z28 will run perfectly smooth and strong if I program the computer to stay in open loop mode all the time, however if I put in my stock programming as soon as the car switches to closed loop it runs like crap. To best describe the problem, during normal acceleration it feels as if the car is pulling tons of timing then throwing it back in. Like power surges, however WOT is still very strong. I have hooker long tubes with offroad y-pipe and when using my stock OBD2 PCM I have the 02 simms connected. I have tried replacing my 02's with new GM ones, replaced the 02 extension wires, I have tried a friends MAF unit. When I tune my OBD1 PCM to run in closed loop it runs like crap as well thats why I think I can eliminate the possibility of bad 02 simms. What exactly changes when the car switches from open loop to closed loop? what sensors does it start reading from etc etc? I know 02's start working but like I said I have replaced with brand new GM ones with no change.
Thanks a lot.
JT

 

A car will remain in open loop only if the pcm times out. After the time-out occurs your SES light will turn on.

If the pcm is receiving adequate signals from the O2's then it will switch itself to closed loop and your car SHOULD run better because your PCM has recognized the O2's as being functional...

 

ok here is what I have done step by step:

when I run my car with the stock PCMforLESS tuned OBD2 pcm the car will run like *** when it switches into closed loop mode and I would get the codes P0133 (bnk1 sen1 02 slow response), P1153 (bnk 2 control shifted lean), and P1133 (insufficient switching bnk 1 sen 1). I got these codes after doing long tube header install. I am almost 100% positive I have no exhaust leaks and these codes showed up AFTER I installed brand new 02 extension wires and new GM 02 sensors. I am also running 02 simms for the rears. Now with all of that said, I bought an OBD1 programmed PCM and it runs exactly the same like crap when it switched into closed loop. I then used LT1 edit and programmed the car to run in open loop all the time and it runs perfectly smooth and feels very powerful.

With those codes I received and knowing that it will run perfect in open loop with OBD1 and OBD2 does anyone have any clue as to what it could be?
as mentioned I replaced both front 02 sensors with new GM ones, brand new 02 extension wires from speed inc, I have swapped out my MAF unit with a friends identical car, and I cleaned out my MAP sensor and ensure that the gasket is sealing. What on earth else could it be? how can the car run good in open loop but not closed loop?

 

Bad wiring is all I could think of...if that's even possible...

Sorry man...

 

Yeah I agree with the possible bad wiring. It could be possible the O2 extensions you got are improperly pin'd. Hope you find the problem...

 

Its your o2s I have same setup as you do hookers, Now I went with the ac delcos replaced both . yes i had got the same code your sensors are going out. low means they are weak and they are not warming up quick enough.. trust me.. get the o2s get the part number hold on I have it right here and then extend them with extra wire sauter.gm part number 25312184 go to gmpartsdirect.com and order they will be the precat ones but from our set up we only have rears.... if you have any prob e-mail me... Angelo if you get the other ones you are gong to pay double because there longer... post cats get pre cats....