I have a Mitsubishi colt with a gen 2 GSR conversion. Around 6 months ago (5000 miles) I installed an AEM wideband, the idea was get this fitted before I start playing with other stuff. Until a few months ago it was working perfectly and other than running leaner than I'd like on a hot re-start (difficult to avoid) my AFR always sat pretty damn close to 14.7 then down to around 12 with 0.7bar boost.
I installed a new head unit in the car which meant cutting up the wiring a little bit as my boost controller, turbo timer, head unit and wideband all run off the same harness which I made up and the following day around an hour into the drive I noticed that my my AFR was off the scale lean at cruising.
It's been like this since except it does respond to throttle inputs, if I blip it briefly then it comes back rich then immediately goes lean before the engine has even settled again. Sometimes on normal driving it will dance around for a while between 10-20 but never seems to settle.
The sensor is fitted just before the cat, at a guess maybe 18-20 inches from the turbo elbow. I've tried giving the gauge a ground directly from the battery which didn't help and I'm reasonably confident I don't have a leak exhaust side. I replaced the 02 sensor today but made no difference and I can't find an air leak anywhere. Car seems to run absolutely fine, at least no different to how it used to.
I've also tried to test the narrowband is switching with a multimeter but my meter doesn't seem to respond very well, it sits around 0.35v and does move around but I don't trust what it's telling me. Running the engine without the MAF or 02 sensor makes no difference, still seems to sit at lean at idle.
Any suggestions as to what would throw my fuelling out like this? Presumably the MAF or air leak?
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