A digression on the subject of tuning and mappers. Almost at the outset of this process I visited a local rolling road (by coincidence they had set up the carbs on my little Abarth engined Fiat 127 for the previous owner), taking my Citroen SM as a pretext, but in order to get some information on their capabilities and interest in helping. That SM was equipped with a Megasquirt ECU.
The owner had recently taken it over from his father who had not long before died, and he was clear of his limitations. He said he had no ability to map Megasquirt as it required a greater knowledge of the set up, and strongly recommended Omex ECUs as Omex gave a lot of technical support. He also cited an example of a car that had not been mapped before, including full ignition mapping, which had taken 3 days on the rolling road with the full support of Omex in the process.
The problem with Omex then as now is that they do two engine ECUs, one for 4 cylinders and one for up to 12, the latter being capable of being programmed for bi-turbo installations etc. As mine is a 6 I really could see no point in paying £1200 or thereabouts for a chip (no loom) whereas the MS2 I bought came with a full loom for my set up and was complete for just over £400. The bit about 3 days of mapping even with support also put me off. The bill for the rolling road could have run into mid teens.
So, fast forward to about 6 weeks ago when I started ringing round rolling roads to get the car booked in. As always I try to be give as much information as possible to aid the person taking the booking. The first one, very local to me, had a professional website stating their ability to set up and map Megasquirt on their rolling road. I called them and even before I'd got out the words Mercedes W114, he stopped me and said they'd lost the lease on the building with the rolling road 3 years ago so could no longer map things. (an example of poor website management but that's bye the bye.) He suggested the guy in Slough I'd seen with the SM.
I then tried one who is featured on the Megasquirt website, they had no number or address and they replied to the email 14 days later. Too late and booked up 'til January anyway.
The penultimate one was local to Bicester and even before I got the words Megasquirt out, I got considerable push back - "you really should have chosen something better, there is little support for it, requires us to spend a lot of time setting it all up etc, really not a good choice, Omex would have been so much better - so you'd like us to help though?" I very politely suggested that actually not really, the result in my SM was spectacular, and I didn't want someone unenthusiastic and not knowledgeable sorting it out.
So in the end I booked Northampton Motorsports who seemed fine with the choice and did an acceptable job on the car. Discussing MS vs Omex with the owner, he did point out that many of the cars that come to them with MS chips are enthusiast built with home soldered chips and so many things to sort that it was a frustrating time for the mapper and for the customer. Also that many different components such as sensors and idle valves came from all over, may not be new or even necessarily working, and getting them all set up is very time consuming. I bought that as a perfectly sound argument, which is why I bought it as a complete package and had all my implementation done by an experienced technician.
The point of this digression, if I have one, is that there is more to mapping than simply an ECU, you need a properly set up car first, but that a mapper may not be able to help you with the time consuming parts of the ECU set up because they lack the specific knowledge of the programming. My Citroen SM programming is superb because the guy doing it, Nard at Renard NL has been experimenting on his SM for several years, has made full use of the open source nature of the MS community to help with ignition timing in particular (irregular beat V6 remember) and so it is really good. Getting all that right using a commercial mapper would be very time consuming and expensive.
So in short, what I am trying to do is use my poor tired and non-technical brain to do much of the work myself, and only go at a pace I can cope with. I am inordinately pleased with my work so far, and am finding it fascinating, but hubris before nemesis. What I want at the end of the winter is a car that is set up properly for all the use I am going to give it and hope in my small way to add a little to the sum of human knowledge of doing it on an M114. This may all go horribly wrong, but doing it all via a tuner would cheat me of so much learning and pleasure, and the money side would hurt too...
Here endeth the digression.
presumably as a function of coil polarity---- again in this case voltage failure would again default to open which makes sense. 
