I get these readings as showed in the graph below from both o2 sensors and I am having a hard time to interpret them, especially sensor 2 (downstream). The readings are from a short drive around town (grey line = engine load). It's not throwing any codes, but that could have something to do with the ecu remap it has. It doesn't pass s/DTC / readiness though, which is my main concern.
Important notice: it's a heavily modified car (Alfa Romeo MiTo TB Multiair) with a catless downpipe. I use a lambda extender/eliminator of the mini-cat type on the second o2 sensor (which worked flawless before).
I tried several things:
- changed 2nd o2 sensor (downstream, post cat) for a brand new one
- checked for leaks between the two sensors (after sensor 1, before sensor 2). There don't seem to be any, but changed the flange gasket before sensor 2 to be sure. Get the same readings.
- Very shortly and quickly unplugged sensor 1 while at idle just to see/check if sensor 1 is reacting and maybe there is something going on over there.. Voltage rises to almost 1V immediately on sensor 1. Which surprises me... shouldn't it be reading a lean condition, thus a low voltage near to 0V?
- changed the lambda-extender/eliminator for a brand new one.
- unplugged ecu to clear it
Nothing seems to have any substantial impact... I hope someone could help me out interpret the graph correctly and maybe point into the direction of a fix.
/Edit: I made another graph from an extended test-drive:
I called a (reputable) tuning-garage today which specialises in Alfa's. They gave me the following information:
- Does not suspect a leak
- Does not suspect a faulty sensor 1 (or 2)
- Uses lambda-fakers/eliminator/spacers of the same type I have on my car all the time (Wagner-tuning mini cat type) without any problems
- Disabling the second lambda-sensor in the ECU could cause problems and thus they always use a faker (I asked if they could just disable it for me)
- Lambda 1 is wideband
- He had the same car model (slightly different engine) on the dyno at the moment we called and he checked the idle voltage for sensor 2 on that car for me. This car gave 0,4 - 0,6V at idle.
So, this now feels like I am set even a little further from home.
I also tried numerous drice-cycles without any luck. The readiness test checks everything except the catalytic converter. The catalyst monitor should check when:
- there are no MIL's and DTC's (check)
- fuel level between 15 - 85% (check)
- ECT above 70F or 21C (check)
- Engine must have run at least 90 sec. (check)
- Engine rpm between 1350 - 1900 (check)
- Idle the car for 5 minutes (check)
- Drive 2 minutes between 30 - 45 mph (check)