So after reading some more it turns out that it's not a straight resistor but rather a voltage source of sorts: http://www.ferrarichat.com/forum/348-355/288970-ohm-specs-355-cat-ecu-thrmocouple.html Therefore I'd like to know whether there are any generic thermocouples that I can fake into the CAT ECU to get rid of this light?
Has anybody tried it? It may work as they won't generate much of a voltage until they are actually warm, so the ecu will just think they're cold (and won't tell you to slow down for cold cats) if you put a resistor in there. At room temp (20C) they only put out a little over 1mv, so the cat ecu would have to be very sensitive to pick up that kind of deviation. Fwiw, according to that other thread, they will only pick up +-68df change, which is around 2mv. I would try just putting in a 9ohm resistor to fool the computer into thinking they're hooked up and see if that works for now. Otherwise, it looks like you'd need to hook up a K-type thermocouple as that has the required temperature range. http://www.omega.com/temperature/Z/pdf/z218-220.pdf The stock thermoucouples do not have to be in the exhaust stream for the computer to be happy and the car does not throw a light even when in the 30's to low 40's F where it would be putting out very little to no voltage, so I think the computer only cares if they are hooked up at all (ie not open circuit) and are under 40mV.
Got (2) 10 ohm resistors and will try it later on -- otherwise I've seen there are some very low cost (probably CHina made?) K-type probes that I can prototype on. If it works I will look at the Omega option, they have a connectorized short probe that can probably be encapsulated in some form of epoxy but I think it's around $75 which is expensive for a dummy probe ;-)
If the ECU had to see a voltage, you could probably just get one probe and split the signal to both ECU's being that it'd be a parallel DC circuit (no V drop). I can't imagine that's the case as at room temp the probe would only be putting out 1.2mV, which appears to be less than the sensitivity range of the cat ECU.
So I was able to run the car today more extended and on the road since I just got my plates... Long story short, the car is rock solid, even with the Slow Down 1-4 light. I checked the Slow Down 5-8 bulb, it's not burned out, yet it does not come on when starting the car (Check engine 1-4 and 5-8, SD 1-4, battery, and brakes flash on then Slow Down 1-4 remains on). This is with Both CAT ECU plugged in and no thermocouple so I guess the alarm from 1-4 is not shutting down that bank? This week hopefully I'll be able to hack a thermocouple since I just found the plug that will fit exactly into the CAT ECU (where the thermocouple goes) and got a third party thermocouple. Finally I will also make an extension cable which will allow me to swap CAT ECUs without actually swapping them physically. I'm also making a test switch for the 95 and earlier cars that have the pigtails hanging out (no test button) - I guess all the Euro 2.7s and 348s have this? It's been a little slow finding and testing connectors, I feel like Dave Helms probably felt eons ago when he embarked on finding the right hardware for the gold connector kit ;-)
