Correct, the generic obd mode 1 requests often are quite slow. This may be for a number of reasons: busy with critical engine tasks, how tasks are handled internally, or even just lazy engineering! But this is fine because most automakers provide a technique for high-speed datalogging.
Quote: Originally Posted by Podaman
Can software (PCMSCAN) simply be re-programmed to say "send me these 30 parameters automatically, without polling"? This would allow us to reach speeds that are 10 times faster for more than just 3 parameters. Or do car controllers have a hard limit on this and can not be overcome until newer cars update their ECUs and remove the restriction?
Sure, the author of PCMScan can add support. It's not in there yet -- the technique is different for each automaker, so covering all makes/models is a ton of work. That's why I'm working on a plug-in so software vendors don't need to reinvent the wheel each time.
The exact performance and limits will vary. Yesterday on a 2003 Ford diesel (CAN), I was getting a two 5 byte repsonses every 8ms. You can pack multiple 1 or 2 byte parameters into a single response. Also you can have ~16 requests that will be served round-robin with the typical 8ms spacing. If it's not 100 degrees outside, I'll try my 03 Mustang today which uses a much slower engine controller.
Quote: Originally Posted by Podaman
with the Mongoose, is this limitation really only in the software? So with a patch that changes the polling technique we could request more than 3 parameters simultaneously at the speeds 10 times faster? Or does the problem lie in the car's ECU and it can not be overcome until car manufacturers update their controllers.
Technically it's not polled -- you setup a request and the controller spews data continuously. From what I've seen Ford and GM support this on all OBD controllers back to 1995. Life was easy because they maintained tight control over the engineering process. But your mileage may vary and you'll always find exceptions!