Let me expalain my set up and recent problem. I have 1999 C5 with stock PCM with dyno tune to accomodate LS2 stroked 402 with D1 blower and NOS and long tube headers. Car is hard where it needs to be to run consistent 9.8's. Car ran great with above set up until I recently threw a P1153 code. I have OB2 so i know what that is and addressed by putting new delco rear sensors in my front sensor location and connected them to front harness with adapter. I know these have to be 600+ degrees to close and have pcm run fuel/air. My problem is once during the beginning of every ignition cycle, I get a pop pop pop at about 1500-2000 rpm for a small time as my sensors don't seem to be cycling high and low enough to allow pcm to do its job.. those of you who know O2 sensors know what I'm speaking of.....basically lazy sensors. Once car is run for a few minutes, problem is gone. I have checked my grounds, all good, alky system not leaking into throttle body at stop or at any time car not under boost. I have rear sensors tuned out. Only thing I have not checked is PCM and MAF.....I'm taking my car to my tuner next week to try to find this gremlin but was wondering if anyone had any comments on this issue. Only thing that is different from when the car worked and when it did not was the install of Mazaries water pump. Ya it's electric but I know how to install and used seperate wire off ignituon switch and new ground to chassis ...did not tie into any existing system....I have 2 LS techs at a local car dealer also helping with this and we are going through the process of elimination but both these guys are not used to working on mod set up like mine but they are good at what they do and say they will find issue but whew its been 30 days screwing with this thing....any help pleaseeeeee

 

Your engine doesn't go closed loop for a minute or so after startup, so it would seem to be whatever your stumble is, it is occurring in open loop, and thus, would not be an 02 problem at all. The fact it goes away quickly after it is running (when it does go closed-loop) seems to confirm this.

It sounds like it's running too lean after startup, and if so, that could be a tune issue, and not likely something a dealer tech would be able to easily identify and cure. They don't deal with custom tune issues, they (and their software) are trained to deal with mechanical flaws on stock-tuned PCMs.

The fact you stated this all started after a water pump install also makes me wonder if the intake tract was removed to do so, and if it's possible something didn't go back together quite right. An intake air leak (post-MAF, if you have one) could be to blame.

Just thinking out loud here. If you had some datalogging software that could record what the post-startup conditions are, it could quickly pinpoint the problem.

 

I have checked all that..actually I have a video from an OB 11 where I have a freeze frame of the sensors going from 400-600...lazy, should be 100-900.......I know about the 100 seconds before they close but the pop comes anywhere from 3-5 minutes after start up......this is really a tough one...I am having my tuner retune it next week and he hasd my old tune so he can compare a few things to see if anything changes like the MAF readout...just for grins I am goiung to recheck for any air leaks but if it leaked would not issue always be present??

 

No more comments..??