any deviation on the remains of the O2 sensors will throw the system in to disarray so any pin holes have to be sorted and must be blanked off, the pre cat O2 sensor has to be left in the system but hung up any where but not in the system this keeps the readings apart

 

yea but if the secondary o2 sensor was not getting any reading I would get a check engine light and it would run rich

 

the secondary O2 sensor is an evaluator so it its out of the system and set cold it cant interpret so lays dormant and agrees with the fist O2 sensor electronically

 

then why do most of the people who put test pipes on create a spacer and keep the secondary o2 sensor still in the loop, and how whould the problem im having be related if it ran well for so long..

 

what the hell Ive been in the auto trade for over 40 yrs and still cant make people understand the little differences the new tech has done

 

it must be removed from the system/ isolated so it cant communicate with the ecm to change values but still in the system if you know what I mean

 

dont get mad im just trying to understand, all I know it was I have seen, most of my background on working on cars doing performance mods has been done with carborater cars will very limited ECU's and programing. My friends a4 dosent have the set up I have and he gets a check engine light.. Just the problem im having started just so suddenly and i never get a check engine light..

 

I never get mad but I understand what you mean ( computer controlled ) so I know where your coming from only problem is what mods you have done and can the ECU interpret it, im always looking for ways to device the ECM and when I find out im sure to let you know but you have to tell what you have done in performance terms for me to calibrate the out come

 

well here is everything I have done. first thing was change the timming belt not a mod but when I did that I also put in a ko4, after the ko4 I bought a Evo DV, and put in the custom cat back and custom down pipe, when the ko4 file I had to add a AFPR and set it to 5 bars. I then did the Air-box mod, and also looped in a MBC with an N75 race valve. since then all of a sudden with no ryme or reason one day i was driving after it got warm and the car started having misfires and would ping when it would spike when I got full boost, ever since then it just would happen once in a great while and it seams to be right when the car reaches its normal running temp, since then i installed a fuel presure gauge to monitor the presure and found that i was loosing presure on acelloration, so then I put in the 310cc injectors and lowered the fuel presure now the presure increases instead of decreases the car runs much better but still has the problem once the car is warm, seams to only really run well after the car has been sitting for a while, it also is hard to start once in a while. It could be a bad AFPR one of my thoughts is that the Diaphragm inside could have been damaged while the presure was dropping and once after it gets warm i get some fuel shooting up into my vacum line that runs ontop of the regulator..

 

thank you for a very informative answer which is what i wanted ( fuel delivery is your problem ) all the rest is ok for now ( performance fuel pump and filter is my guess )