Slowing up the stftrims coming in so early.

[alian]

I seem to have a problem having the short fuel trims leaning out into the high 15s way before the car goes into CL. when looking at the log you can see the trims pulling it outthen releasing. I have Ltft off but cant find where you can control the time orhow far they can pull the afrs out. When I go full Open Loop I dont have any trouble of it leaning out.What do you rekon???
Cheers Ian

[alian]

Here is a pic of the problem I seem to be having. Like I said when I am running in OL I dont have this problem. Any Idears???
Cheers Ian

[swingtan]

I remembered how to do this.......


Set B1501 and B1503 to the same values. I run 120s @ -40' and 10s @ 68' and higher. From -40' to 68' I linear fill.
Set B1502 and B1504 to the same values. I run 85' @ -40' and 50' at 20' and over. Again I linear fill from -40' to 20'. You may need to alter these for your climate.


My theory on this is that the E38 will start using the O2's to trim fueling "before" it enters CL mode. So it will try and trim the mixtures while in OL mode and attempt to correct when it probably shouldn't. Setting these table the same for CL mode and O2 ready tests results in the ECM only using the STFT's when it has entered CL mode. This stops it leaning out the mixtures while the engine is warming up.

Simon.

[hymey]

Hi Simon,

Thanks for the reply. I think Ian is having trouble more so at hot start with higher ects. I have occasionally seen this issue. If the engine is already hot then times for 10 seconds before CL starts it appears to be tied in with the e38s tendency to go lean with mafless tuning on hot start for 8 or so seconds. What helped with mine was to establish CL after 25 seconds(set above 80 deg C) with B1501 and B1503. This allows correct OL fueling adjustment to compensate for hot start so we are in the low 14s for the period of 25 seconds, Not 17:1 like sometimes we see from either poorly setup OL or conflict with CL starting to early.

[swingtan]

Oh, OK. I was going buy the image of the ScanTool screen where ECT is 40'C. In this case I'd lengthen the O2 and CL times a bit and use B0147 to add fuel. I found that the "hot lean out" generally occurred when the IVT was under about 120'C while the ECT was over 70'C. Holding OL longer and using the IJT Multiplier fixed things up for me.

[hymey]

Oh, OK. I was going buy the image of the ScanTool screen where ECT is 40'C. In this case I'd lengthen the O2 and CL times a bit and use B0147 to add fuel. I found that the "hot lean out" generally occurred when the IVT was under about 120'C while the ECT was over 70'C. Holding OL longer and using the IJT Multiplier fixed things up for me.

Thanks Simon, In OL mines fine only in CL when the O2s try to start to early it goes lean for about 3 seconds although doesn't appear to cause any issues and only occurs every now and then sometimes even when the motor is colder. I basically made IVT settings more aggressive in CL and played with injector multiplier which appeared to help. Its only since I have had the big cam it has done it.

cheers

[alian]

Yes that was a cold. Have done a couple of things, 1 was to align 1501 and 1503, 1502 and 1504.Not sure how long they have been different. Will have to go back to see when and if they were changed. I seem to have come up mwith a happy medium that is working for me. Thanks :master:Simon and :master:Joel. Again you have proved that the more you play the more you learn.
Cheers Ian

[swingtan]

RE: the timing for them being different...... they are not the same in the stock OS. I;m not sure why you would want to start using fuel trims before entering CL as you are most likely going to be commanding something other than stoich. In this case, the trims will kick in and attempt to pull the mixtures back to stoich. The only thing I can think of is that this is done to deliberately skew the LTFT in one direction, in most cases, it would be to lean them out.

Simon

[joecar]

Sounds plausible... GM must have had some reason to do that.

[swingtan]

Yeah, maybe they knew that the tunes would go rich over time, so they did this to help lean out the LTFT's. I don;t know, I just think it'd be easier to do it right the first time...... :p

[hymey]

Yes that was a cold. Have done a couple of things, 1 was to align 1501 and 1503, 1502 and 1504.Not sure how long they have been different. Will have to go back to see when and if they were changed. I seem to have come up mwith a happy medium that is working for me. Thanks :master:Simon and :master:Joel. Again you have proved that the more you play the more you learn.
Cheers Ian

Ok its strange that its leaning out there. I can normally here mine go into CL when its warming up by 60 degrees STFT kick in and the engine note changes. But its not lean, only when hot I had this trouble.

[alian]

Ok its strange that its leaning out there. I can normally here mine go into CL when its warming up by 60 degrees STFT kick in and the engine note changes. But its not lean, only when hot I had this trouble.

Joel This is a problem I have had since I started tuning the car. Once I had tuned it maffless and went to turn on the sftrims it was doing it. It is the reason that I have always stayed with an OL tune.Now it seems to be working, But I will do some more testing at different heat temps.
Cheers Ian

[gmh308]

I have seen STFT's start up 3 sec after a cold (warm ?) start from memory. Stock tune. So maybe this is the same thing.

[hymey]

I see the advantages of stfts as simon has pointed out. On open road trips my economy improves in CL around town its better in OL. But overall CL is better with the e38. It has its niggling issues from time to time. 3 seconds I have seen this too. I too go through times of using OL and improving low speed tune. Using the MAF solves a lot of things and my drivability is better although I am down 2-3 kpa with MAF on.