Next chapter, chaps...
Today we made the twin O2 sensor setup. I put another O2 bung into the PS Iida downpipes. There is a brand new narrowband one and next to it the PLX. Obviously there is no narrowband emulation from the PLX to the ECU anymore. Instead the narrowband sensor is connected directly. However, it did not change the situation, still too lean on hot idle (between 16ish and 17ish AFR's
So what I can say is - the PLX narrowband emulation
does not cause this abnormal engine behavior!
We then began to check other sensors and values, such as engine coolant temp, ISC valve and base idle. We laso performed a full setup for the TB (inc. fixed SAS, TPS and IPS). Checked for air leajs - nothing. No change of Situation whatsoever.
What we found:
- base idle barely at 650 rpm [acc. to workshop manual] but ISC has 0 steps and base idle screw fully closed -> not correct
- no leaks in exhaust or intake piping, no hissing sound etc.
- even though the IPS/TPS is setup correctly the ECU does not sem to get the IPS signal - it always displays IPS = off.
- the injector time is slightly going up from 1.8ms to 2.0ms seconds
We then disconnected the FPR from the solenoid driven pressure source and connected a manual vacuum/pressure pump. Neither with 0.5 bar vacuum nor with 0.9 bar pressure the AFR changed. So now we are kind of clueless. I tend to believe that the ECU tries to get this "lean conition to be rectified but it cannot reduce air more (because ISCV is at 0 steps already = fully closed) and even with longer injector opening times it does not get more fuel.
Does that mean, the FPR is the culprit? Why is it working spot on under WOT or hard accelerating then? When cruising the car perfectly fine swings around 14.7 AFR. When on WOT it gets 11.5 without issues.
What does the IPS signal trigger inside the ECU? Is the factory FPR capable to handle a 255lph Walbro on constant 12V (e.g. if I am going to bypass the resistor pack in engine bay?
In fact the situation does bug me. It's kind of "luxury" problem I am chasing, as it's only happening during idle but I know it's not correct and it will be an issue for next year's MOT/emmission test. So any ideas are very welcome....
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