But without a wideband, you don't know what those "trends" represent. -3 +3 from what? 13.5? 14.5? 15.5? Unless you know the target the ECU is aiming for, you won't know what it is off by. The trims are just a rudimentary number at that point.

 

100% not true. Open loop by definition means o2 feedback is ignored.

 

You are incorrect. LTFT is applied during open loop. Watch the output on an OBDII data logger.

 

the direct o2 feedback is ignored (and therefore no adjustement is made to the trim tables) but the existing information in the LTFT tables is used in Open Loop as far as I know (as input).

Btw, the emanage I have, is tuned to perform closed loop fuel control while in open loop.. but i can't monitor those trims via OBD2 (since it's using the feedback of the additional wideband installed)

 

I agree that LTFT is applied (not adjusted) during open loop. If it wasn't applied, then the car would run like crap at full throttle as the car gets older.

However, I really doubt the eManage runs in closed loop at full throttle. After developing my own piggy-back ECU with wideband input, I can tell you that things are changine MUCH too quickly to do real time AFR control. What I believe it does is to make small changes, monitor the results, and apply changes for the NEXT TIME you go WOT. If it makes incrementally small changes to the fuel curve based on the previous runs, it will fine tune itself slowly over time.

 

According to the manual:

I guess that the one that knows exactly how it works is Giles.. (and I don't think he will give that many details for obvious reasons..)

 

That quote describes almost exactly what I did above. It is technically "closed loop" in the sense that it is monitoring the O2, but it isn't closed loop in the sense that the stock ECU does it.

The stock ECU doesn't store STFT at all. It only stores a running average of it that is not based on RPM at all (LTFT). When the factory ECU is in closed loop, it tries to maintain stoich in REAL TIME by agressively adjusting fuel on the fly.

A piggy back like the one I built and the eManage will not try to do this. It will monitor the O2, see that it is rich or lean, then make an adjustement to an array of "fuel trims" (ie. maybe 100 fuel trims values stored in memory by RPM index). The next time the engine hits that RPM at full throttle, it will adjust fuel by the amount it stored in memory from the last pull, then monitor the O2 again to see how close it got. It will then calculate another adjustment to use the next time, and store it in memory again. The disappointing thing is that according to your quote from the manual, the eManage erases that data every time you turn the car off. My piggy back did NOT do this, so it maintained its tune over time. That's disappointing ...

 

The OBD2 logger shows the trim from the ECU because it is a stored value. It is not being applied I can assure you. If it was, piggybacks like the VAFC2 would be useless.

So explain this: how does my 400whp car run the same AFR everytime I go WOT with closed loop turned completely off? No short or long term fuel trims measured or applied.

Realize this: partial throttle is harder to tune because of the variables involved. WOT is easy in comparison because its a linear transition through the RPM's and it is operation is not concerned with fuel economy.

 

You are correct the LTFT is a stored value. Saying piggybacks would be useless if it was applied during open loop is incorrect. It is just another variable you have to account for. It doesn't change very much, mine tends to hover around 3-5%. The reason it is applied during open loop is to account for changes in VE of the engine. It allows some amount of correction to be applied to the factory tune to account for aging engines, bolt-on modifications, etc.

As to your second paragraph, I don't know anything about your engine management setup and can't draw any conclusions.

I fail to see how your last paragraph relates to the discussion at all.

 

If LTFT wasn't applied during open loop, then there wouldn't be so many people complaining about how the ECU slowly learned to compensate for their VAFC.

One of the big purposes of LTFT is to compensate for slow changes in the way the engine runs (clogging fuel injectors, dirty air filters, etc.). If the engine always runs rich due to poor air flow, or always run lean due to clogged injectors, then the LTFT should be applied during WOT to prevent it from running too lean or too rich.