Originally Posted by DangerousDan

this is not correct. the ecu will still have the same abilities it had before the piggyback. the only thing the piggyback does is modify the signal coming from the MAF. It is two dimensional, RPM vs Voltage, and only changes one value. you are tweaking a map in the piggyback, which is really halfway tweaking a map in the ECU, and this doesn't affect any of the ECU's ability to extrapolate values for it's map using other sensors.

that being said, offsetting the values WILL affect how easily the ECU overcomes changes, which is probably why some of us are seeing the season changes change our tunes. I would hypothesize that because we are changing values at one temperature to make it ideal when the temperature changes again the ECU still compensates for the change but with our modification on top of it it throws the ECU's calculations off. we are modifying one signal (a primary signal for fuel) out of many that the ECU uses to calculate fuel, and even though we know what this signal means we don't have any idea what the algorithms look like.

think of it like this. the ecu draws a a wiggly line. you use the piggyback to make that line straight by changing the values the ECU gets to see from the MAF. then the sun goes down and your temps drop. the ECU is still drawing a wiggly line, but the peaks are all moved around now due to the temperature change. your values in the piggyback aren't going to make the line straight any more, are they? your ECU just adjusted, but the tune you have on the piggy is no longer ideal. the further you move from the tuning conditions the further off your tune will fall.



you are over simplifying how this system operates. for one thing the IAT sensor exhibits known resistances at particular temperatures; it's not a hot-wire sensor. while the sample rate of this sensor is probably affected by instant temperature changes it's pretty likely it can tell the difference between -10* and 75*.

as for the base tune, it's been proven to be lean on some cars. This was before you became a member, so it's not like we expect you to know this, but we aren't just saying it.

In summation, modifying the signal coming from the MAF isn't really going to limit your ECU's ability to compensate for atmospheric changes unless those changes are quick enough to put you far outside your current conditions. tuning on a dyno in SoCal (especially when you aren't even using the same car or even mods) and immediately flying the piggyback to Ontario for installation is going to show you exactly how much outside temperature and altitude matter. your cars stock tune is drastically different between these locations (open loop) so your base tune is going to be way off.

I'm not saying you'll blow your engine, but do you think 16's and 17's are good target AFR's for a base tune? I don't