Cool stuff and canbus...

Well, it’s been a while since there’s been an update on FrankenBoxster in this blog….
And it’s also been pretty cold in the garage lately:-)   

So the car made a triumphant appearance at Oktoberfest!
And it went there and back under its own power!

Hope you enjoyed the video, it was from this year's GCA presentation (thanks Shawn and Kevin).  So as I was saying.... Frankie made a triumphant appearance at Oktoberfest – and it went there and back under its own power!  I am also fearful that it went there without the cooling fans running on the first leg!  Upon my arrival at Oktoberfest I was so enthralled with showing off the car’s abilities that it took me a while to notice an eerie silence (if you could call it silence over the exhaust’s din), the silence was from the lack of cooling fans running. Surely by now it should be hot enough to kick the fans on? Sadly the temp gauge seems to follow a normal warm up curve and gets to 185 and then never goes higher? What’s up with that? (figuring that out will be most likely be in another blog installment)

So…… I go into the rear trunk and pull the interior covers revealing all the wiring, computers and relays that I had spent hours making pretty/concealing before Oktoberfest. I proceed in undoing all of the pretty tidying up to get to the cooling fan control relay I wired in and unplug it – this makes the Porsche Cooling Control computer in the front trunk think it’s lost communications to Main DME Computer in the rear trunk and puts the fan circuity into “fault mode” which spins the fans up to full speed! BTW I drove it home this way… I guess I should now take a moment and talk about CANBUS.  Ugh:-(

Think of CANBUS as a local area network (LAN) but in your car. I cannot even begin to tell you how much this has complicated FrankenBoxster’s creation!  CANBUS is pretty much in all cars nowadays, and it is really a great idea – for example; instead of having a huge bundle of wiring with wires running to every gauge/idiot light in your dashboard back to the various senders in the engine compartment, etc - you can just run a 2 wire BUS between the Controller Computer on the dashboard to the Controller Computer in your engine compartment (DME) or to the Cooling Controller etc… and just sent messages back and forth to everything over two wires. Saves miles of wiring in your car! And I’m up to 14 different computers I’ve found in my Boxster thus far. They are simply daisy-chained with a twisted pair of wires and merrily talk to each other about what’s going on and keep things running on the straight and narrow.  Got to love technology.  Have I lost you guys yet?  Now back to Frankie’s cooling fans….

Sadly in the world of CANBUS a Porsche DME doesn’t simply “talk” to a Chevy PCM, so other arrangements have to be made. In the case of the cooling fans, I put in a relay with the Porsche cooling control computer reference voltage signal going through the normally closed contact – and then wired the Chevy PCM fan controller voltage signal, which is energized at 185 degrees, to pick the relay which in turn opens the normally closed leg thereby dropping reference voltage signal to the Porsche’s cooling control computer making it go into “fault mode”. Once this particular computer goes into “fault mode” it turns the fans up to full speed as it believes it has lost access to the CANBUS to receive messages telling it what to do with the fans… when in doubt spin it up!  Guess the Porsche engineers thought than any fault should have safety protocols that error on the side of caution and run the cooling fans. I’m not even going to tell you how we tricked the Driver Safety Computer into thinking the clutch pedal is down and allow the starter to engage when you turn the key.
 
Our next blog installment we’ll talk about getting the temp gauge to read accurately – bet you can’t wait!  If you’ve still reading this – I really have to thank you for hanging in their!!!   Your Pres (Doug:-)