does a PFL ecu store long term trim?
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does a PFL ecu store long term trim?
Not really. In our testing with Ryan's car and EVO scan the fuel trim would drop down to 93 octane points or so when flooring the car and after a acceleration run or two with throttle between 20 and 50% it would go back up to 100 fairly quickly.
i thought as much.
is there a way to change or trick the ecu so that it dosnt ignore O2 sensor and revert back to its own map?
practical or not im curious but i dont know enough of the ecu :(
I don't know specifically with the VR-4 ECU, but there are tricks with the TPS signal that can be effective.
I would be interested in looking into this if you could point me in a direction to do some more reading :)
I can't prove anything, so take what I say with a pinch of salt, but I believe:
The car has two distinctive settings:
1. Low throttle, O2 feedback.
2. Wide open throttle, pre-defined fuel maps.
I personally believe that the O2 feedback takes much longer to re-adjust itself than the WOT settings. The octane setting reduction/recovery that Brad talks about above is a WOT way that the ECU trys to stay in control of a dodgy situation. The dodgyness is measured using the cars knock sensor - too much knock and the octane setting is reduced. This will recover as Brad says, under medium acceleration. (Assuming your car is not knocking under medium acceleration!!) It will not recover under very light throttle, when the car is in O2 feedback system.
Like I said, I believe these two systems to be completely seperate and self correcting over time. I also believe that the O2 feedback fuel trims take much longer to adjust than the octane rating under WOT.
Why would the 02 fuel trim need to take into account change in octane while at WOT. In transit refueling?Quote:
Originally Posted by Nick Mann
Ok - lets through a twist into it.
With piggyback controller, it is taking in the O2 feedback and running on a preset map that you have created and sending it to the factory ECU which still controlls the injectors.
At WOT I take it that the factory ECU is trying to revert to its own preset fuel map. Does this happen or does piggyback ECU take in the TPS as well and output a lie to the main ECU?
It depends on the piggyback: they don't all work the same.
Most of the ones I've seen take wholesale control of the injectors, and interpret the output signal from the factory ECU: more of a pass through than a piggyback.
However, as you say, some simply tell fibs to the factory ECU to adjust the fuelling. This is, however, a dreadul way of going about things, as you end up with completely the wrong ignition timings: a recipe for a horrible car to drive and very bad det in places.
I don't know for a fact that the VR4 ECU works this way, but it will be the first "second gen" ECU (i.e. full EFI with memory, not just a ROM) that doesn't have a set of overall governance variables. So, for example, knock correction on WOT can (and will) have a trim effect on the whole ECU behaviour. How this effect occurs varies:
On some, the closed-loop mode uses a "Scoring System". So whilst knock management may have been invoked at WOT, the number of knock events in a given time were sufficient (after knock control) to produce a low score: Closed Loop running remains unaffected. However, continual knock events over a given time period, will result in the closed loop trims being altered.
This will usually manifest itself as a longer term "octane" trim, and will usually result in an increase in bias towards the "safe" maps at interpolation.
This will be a change will be global across "Open Loop" mode....not just WOT (and lets not confuse the two as they are different!) Whilst the lamda sensor will mitigate the impact of this change during closed loop, let's not forget that the ECU drops out of Closed loop the minute you change the throttle, or engine load changes significantly (as measured at MAF) or, of course, Knock is detected. Other things, like Fan Start, Aircon start or even PowerSteering may have event flags that override closed loop mode.
All of these will be influenced by the long term trims associated with octane.
Whether this would be an issue on the VR4s paranoia-level partial throttle change, I couldn't guess.
TPS alteration tricks can vary dependant on the sensors used, but one trick is to "clamp" the TPS output, preventing the ECU from realising Open Loop mode. It can also be "smoothed" which removes the ECU seeing any sudden throttle changes. The catch here is that the ECU is still watching the MAF, so how it behaves in these scenarios can be unexpected: Many simply throw a CEL and resort to safety mode. Others will log a fault event, but get over it.