[jonzobot]

Hello everyone,

Long time lurker here, this is my first post!

I am presently making up my own version of an MPGuino from scratch, using T Vago's latest software - which by the way is amazing and he deserves much praise for doing all that work.

My car is a 1999 Toyota Tercel. I believe (but I am not 100% sure) that my car suffers from the same problem as the Chrysler returnless system. The returnless systems on the Tercel only made a brief appearance in the latter part of the model's existence from 1997-1999. Not having a shop manual, and trying my best to Google information leads me to believe this is NOT a computer-controlled regulator pump, but instead a mechanical in-tank pump and regulator. The pump supposedly cycles on and off to maintain a constant pressure (roughly 48PSI) over atmospheric. Also, it is possible that the fuel pressure changes with fuel / vapour level changes but I am very short on those details. I do not see a fuel pressure readout when plugging in an OBDII reader, instead I have to screw in a gauge to the fuel rail.

If this is the case, this means that as manifold pressure changes, then the pressure differential across the injector will also change, and this will throw off the MPGuino numbers, since the pressure drop will cause less fuel spray in a given amount of time.

My questions are:

1) Does anybody have any bright ideas on how to tell if my car has this issue, or not?
2) Is there a list of cars that are confirmed to have this issue?
3) Is there an additional issue here in that as fuel level changes the fuel pressure also changes which will also serve to throw the numbers out of whack?

Also, an unrelated note, on the MPGuino schematic diagram on the wiki, shows 50k resistors for the VSS and Injector leads, but the Iduino shows 100k. Not sure if that really matters or not (oddly I have seen the same diagram with both values) but I went with the 50k.