Are trims ever added to fueling when in PE?

[Chalky]

It's winter here and car is put away. I keep seeing debates and threads on a popular forum. I could be wrong but added trims to car going into OL just seems like something else skewing AFR in OL. I am not even sure how you would check this reliably.

[swingtan]

Most people would say that OL mode = No fuel trims, which is basically correct.

However, PE mode != OL mode and LTFT's can be applied, while STFT's are not. To further complicate things, some controllers ( E38 for example ) will actually apply LTFT's when in OL mode as well. This can be seen on cold starts before the NB O2's have warmed up.

To ensure you get the right answer, log both STFT's and LTFT's and see what is going on. If the values are anything other than 0%, then you know they are correcting.

Simon.

[Chalky]

Thanks for the quick response. I'll check it out when snows clears. >

Just curious but in regards to E38, if LT's impact PE when in OL, if trims are negative, is fuel pulled?

[swingtan]

just a point.... PE Mode is NOT OL Mode (E38 anyway). PE mode is actually CL Mode with a different commanded fuel ratio. So yes, if the LTFT's are negative, they will pull fuel when in PE Mode. At least I'm pretty sure that's the way it works. I've had LTFT's disabled for about 3 years....... I might re-enable them just to see if I'm correct or talking total rubbish :p

Simon.

[Chalky]

Have I been wrong on this then? I ran car on dyno and logged info. When car went into OL, AFR was following PE Table values and both LT/STFTs went flat @ 0. Is there a different table in e38's driving afr values other than B3618?

[swingtan]

Like I said, I'm not sure that LTFT's will still be used in PE mode with the E38, STFT's will definitely not. In your case, the LTFT's may have not had sufficient data to do any correction, or the fueling may have been spot on so the correction was "0", or the controller may not use LTFT's in PE mode. Remember, PE Mode is NOT OL Mode. With the E38, OL mode is not actually OL mode as the LTFT's will still be used....

There's a thread on cold start fueling that shows how the E38 applies LTFT's while in OL mode. You can also see how bad it is to disable the STFT's to tune the VVE / MAF and to not clear the LTFT data. The parameters available for the E38 only control when the LTFT's can learn data, not to turn them off / on. So if you disable LTFT learning and leave the current data intact, the LTFT corrections will still be applied. I don't think I can stress that point enough, as the tendency is to think that "disabling" the LTFT's in the E38 tune, will stop any LTFT corrections from taking place. This is not correct, as you will have only "disabled LTFT learning" leaving any existing correction data in tact and the ECM will use that data to correct the fuelling. This will result in a VVE / MAF calibration that will be accurate until the ECM is reset, at which point it'll be as bad as it was before any tuning took place.

I'm starting to think that LTFT's are not applied during PE mode though, I may have been mistaken there.

Simon.

[Dieselman]

I'm starting to think that LTFT's are not applied during PE mode though, I may have been mistaken there.

Here is a screen shot that shows positive LTFT's during PE



What Simon said about clearing the LTFT's data during VVE adjustment can't be overlooked - I learnt the hard way that it will alter your final results AFTER you finally clear the data. Then you will need to start the whole adjustment process again because all the data will be out

Ben

[joecar]

LS1B: at WOT (PE should have already enabled by now), positive LTFT is added, negative LTFT is ignored.

[ notice I carefully chose my wording ]

E38: I have no idea, but swingtan is knowledgeable here.

[Dieselman]

Just to be clear, my above screen shot was from a E38 controller

[swingtan]

Where's the "thank" button?????

joecar has it! during PE mode only positive LTFT's are utilised, so the ECM will never "lean out" the mixtures, only "richen" them. This is probably why I was second guessing, as I remember the trims having an impact but couldn't prove it in any logs I had.

Good work as well Dieselman, that image proves what goes on in the E38.

Simon.