E38 idle tuning

[gmh308]

One area worth looking at now that Ross & Paul have added them in are the airflow VE Compensation factors. These do influence the VE on a zone by zone basis to optimise mixture control on a dynamic basis related to MAP, TPS, related deltas/nearby history of both, and I think (maybe Ross could confirm...) Air Per Cyl. Not necessarily straightforward, but they do influence transient conditions and definately play a role in initial start up and "tip in" response.

[The Alchemist]

see attached log:
doing some tuning today on said vehicle and noticed that after reflashing and starting engine the STFT's stay high at 8 to 10% for a minute or so then do this transition down to -3%, once it does this I can start tuning etc etc see 18:46:39 expand to 18:47:08 and you will see this transition occur. It does it every time after a new start. everything stays constant while it does this AND it appears the AFR sits around 15.6:1 then transitions to a nice 14.36:1 when this happens. Car is in MAFLESS mode at the moment doing VVT.
Any ideas fellas?

Mike

[swingtan]

Are you running stock NB sensors or are you running a NB sim off the Autronic? The Autronic looks to be giving bad data and if you're running a NB sim based of it it could be causing issues. It's a bit difficult to see what is going on as the WB signal doesn't give a good view. It'd be better if you could confirm the actual exhaust ARF to see if the trims are actually doing the right thing.

Are you saying that the AFR's during the first 1:47 are sitting around 15.6:1 ? How are you checking this? If this os correct, then the trims are not doing what they should be doing, keeping the AFR's at stoich. If this is the case, it's very strange....

If I assume that the trims are working correctly, then you need to look at IVT. Note that the trim transition occurs right at 120'C, I exclude all data under 130'C when doing normal fueling corrections, as under this value the fueling becomes erratic as the engine warms up. It's possible that dynamics are influencing the fueling as in many E38 tunes, there is a change at about 120'C IVT in the evaporation tables. There is also a change between 40 and 60 kPA MAP, which seems to tie in with where you are dropping in and out of gear in the log. I'd be very interested to see what this did if you put the MAF back on, as I think you'll find the dynamics would behave better.

To fix you exact issue though, I'd probably try adjusting B2014, increasing the values below 120'C by maybe as much as 10% down to 72'C. The issue is that the E38 bases much of it's fueling on IVT, not as much on ECT. But at hot start, IVT=ECT, which is well under normal operating temp.

Simon.

[The Alchemist]

Hi there, did another cold start with 1 of the twin tail pipes blocked with a piece of wood
got great AFR readings this time for you to see. The NB o2's are the factory ones being logged and the WB in an Autronic unit on the dyno.
As you can see the AFRS are indeed constant during this transition yet the NB o2's show a 13% swing.
Thanks for the advice. Will look at B2014 for the next cold start tomorrow and during hot starts today.
Cheers,
Mike

[swingtan]

Hang on..... what are the LTFT's doing during this time ?

[The Alchemist]

turned off

[swingtan]

OK, was just checking. Thought they may have been involved.....

Post the tune so I can compare some settings.

[The Alchemist]

Heres a full cold start done today.
You can see the transition occur at 80deg C but this may not be the only thing that determines when this happens because it does that same thing on a HOT start at say 90deg C but only takes between 30sec and 1min 30sec after starting also at varying Intake Valve temps which is strange.
Also worth noting is that the trims go from +8% down to -3% with everything else constant so something must be "removing" fuel from the base fuel calculation while it is in closed loop ie a multiplier of some sort that then turns off at some predetermined setting.

This time I also logged actual O2 voltage and they appear not to be switching very well although they improve once you run the car under a bit of load at 2000rpm or so.
Can you PM your email and I will email the tune.
thanks,
Mike

[The Alchemist]

Today I did a full open loop cold start AND logged pulse width this time, interestingly it seems to jump 0.5ms over a certain load/pulsewidth/whatever and jumps back again when you lower the throttle slightly. The VVT mapping is smooth here with no steep transitions at all.
This may have been the problem I have been chasing, should have done an open loop cold start ages ago !!!
Of course this translates into very lean once warmed up over 80deg and IVT multipier down to "1" and then just right at 14.2:1 when it jumps up the 0.5ms.
Any ideas what is causing this...The injectors are FAST 65lbs ones and I have only reset the flow base setting and not touched anything else...(I know I know I'm meant do but can't find any data for them).
I have stepped the pulse width scales so I could see both of them...
thanks,
Mike

[The Alchemist]

on topic with idle settings I have found this works well for me, engine has a mild cam 225/230 591lift and a supercharger:
b1651 1.02
b1652 1.06 (hot only) during setting up not enough for a cold start
min idle airflow in park neutral at 800rpm around 9.3g/s and ingear around 9g/s

following your other suggestions for the integral/proportional stuff seemed to work well and relaxing the spark idle control.
average readings were as follows:

idle neutral 800rpm > SAE.TP 18.8% sspark 17deg average
in gear 800rpm > SAE.TP 18.4% spark 21 deg average.

what I could not seem to do was go open loop by maxing out minimum idle air to 63g/s and zeroing out the correction pids b1843/1845 as per this thread.
When I did this it didn't matter what I commanded in b1651 (I went from 0.5 to 3) all I got was a SAE.TP of 22% flatline and a high idle of about 1200rpm???
What have I done wrong?
Was adjusting b1651 when I shud have been adjusting B1652 stationery
worked at treat, just got to do a cold start now and tweak 51/52 to reach target idle and we're done. thanks Hymey and Swingtan !
Cheers,
Mike