[CrisZenithBlue]

hi guys,

2.7L 2000 boxster with 140k miles on the chassis and 35k miles on the engine

i've been having these air/fuel mixture problems on and off since i bought the boxster two and a half years ago.. who hasn't?
used to be a simple MAF clean and a reset and they would go away for a few months.


now i have a CEL that stays on and the following codes:
P1128 - Oxygen sensing adaptation idle range bank 1
P1130 - Oxygen sensing adaptation idle range bank 2
P1126 - Multiplic mixture adapt lower load range B 1
P1133 - Multiplic mixture adapt lower load range B 2
P1132 - Multiplic mixture adapt upper load range B 2 exceeds limit value

car is running fine except for a slightly bumpy idle. no power loss when i'm on it.


here's what i've done over time not necessarily because of this but to help paint the picture:
1. replaced AOS about 20k miles ago when it went bad. pretty sure AOS is fine still, no bad AOS symptoms
2. just replaced MAF with new BOSCH one (with durametric MAF showed a steady 13.6 - 14.0 kg/h at idle.)
3. replaced O2 pre cat sensors on both banks with OEM ones.
4. did a vacuum leak test at Vertex in Miami and they didnt find any leaks at all
5. i was suspecting a fuel delivery issue so i did a fuel pressure test. it stayed flat at 3.2 bar (i know the range should be between 3.3 and 3.8 bar). I would say that's not bad, maybe a bit on the low side (fuel pump being a bit tired at this mileage? maybe just the gauge was a bit off? cheapo one..). when revving and keeping it there the gauge would move slightly then be stable again under constant gas. I forgot to pull the vacuum hose from the regulator with the fuel pressure gauge on to check it but when i pulled it after it had a good sucking pressure.


when i had the durametric connected I checked the O2 sensor voltage and all looked good (ranging from 0.10 to 0.75-0.80) except for O2 sensor voltage behind cat conv bank 1 which showed a static value of 0.08 volts. after cat O2 sensors are original that came with the used engine. i plan on replacing both next so i have a full set of brand new sensors all around.

could this one O2 sensor cause the issue i'm having? i was thinking that an after cat sensor would be less important but they do all talk to the brain of the car for that perfect mixture.

i'm also thinking my fuel pressure is a bit low? what do you guys think? it's just a tad low, enough to throw more air in the mix and throw all these codes as if it were running lean. if it was lower i would probably have power losses but i'm good there.

i tend to believe the injectors are fine being low mileage (i use nothing but shell gas) and because i had these issues before and after the engine replacement but i might be wrong. I dont want to throw money at things unless i'm out of options.


what do you guys think?


thanks in advance,

Cristian