So my Megasquirt updates and lessons learned:
1. My first unit has a bad processor (I bought two used, unknown condition MS1 units from a friend a few years ago). This gave very weird readings and was confusing as hell.
2. There are two gauges in Tuner Studio which can display your O2 sensor. Front Bank and Rear Bank. I don't know much about why they work like this, but the front bank gauge I was originally using had a .2v offset, which is too much when you're only talking .1-.9 full sensor swing. Rear bank reads fine.
3. I had a bad TPS. It would sweep nice and smooth, but upon startup would start very quickly to give negative throttle positions. Also confusing. Eventually I swapped it with another used one and the problems went away.
I just started tuning it in the last day or so, fiddling with the warm up enrichment and what not, but have to get my fan wired up again. This is a long time coming, as I've probably had the parts for 5 yrs already, just never got around to actually doing it! Although you can mod the MS1 boxes to control a fan, I'm just making it separate, using the BMW radiator mounted switch and a separate relay under my battery box for a relatively clean installation.
The sensor uses a fine thread M14x.... which I didn't have of course (I had a FINER
one...M14x1...which I've not used EVER
) BUT, it just so happens that I had some nuts which were the right thread and welded one onto a wrought "T" to put on my heater hose line (since there's no shut off valve to the heater). The sensor also has a red fiber/rubber gasket of some sorts on it already, so I'll use some Loctite thread sealant on the threads and hope the little fiber washer thingy takes care of the rest.