jfitzpat -
Quote:
Originally Posted by jfitzpat
...
Via OBD-II, we have some additional challenges. MAF is a 16 bit measurement, 1/100 g/s, but MAP is pretty course, just one byte and in kPa steps. Second, there is the question of ecu speed. Take a typical pre-CAN Honda, say early 2000-somethign models. They are talking ISO 9141, and pretty slow. If you are polling MAP, RPM, IAT, and VSS. You are getting a full set of readings roughly 1 or 2 times a second. So you are getting snapshots of engine performance that are pretty far apart. In addition, the samples themselves are offset from each other in time.
Now, there are some tricks that could be used to refine the measurements, but, in general, I think these sorts of things are better as 'relative' measurements. I am using more fuel, less fuel, that sort of thing.
Sorry for the long post, but I just talked to someone else about this a few days ago.
-jjf
|
I have an old Scanguage I. But, I also have a scantool setup I occasionally use for datalogging. It uses the
ELM 322 chip. It has been my impression that my 1999 ECU/PCM is slow to respond to commands. I very much agree that scantools do not get all the data as a "crisp snapshot in time", but as a "blurry picture over time". It also makes me wonder if the ScanGuage limits it's instant display to 4 items for the sake of manageable bandwidth (in addition to LCD real-estate).
CarloSW2